--- AnyEvent/lib/AnyEvent.pm	2008/04/22 05:12:19	1.54
+++ AnyEvent/lib/AnyEvent.pm	2011/08/13 02:35:32	1.358
@@ -1,24 +1,60 @@
 =head1 NAME
 
-AnyEvent - provide framework for multiple event loops
+AnyEvent - the DBI of event loop programming
 
-EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl - various supported event loops
+EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, Qt
+and POE are various supported event loops/environments.
 
 =head1 SYNOPSIS
 
    use AnyEvent;
 
-   my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub {
-      ...
-   });
+   # if you prefer function calls, look at the AE manpage for
+   # an alternative API.
+
+   # file handle or descriptor readable
+   my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ...  });
+
+   # one-shot or repeating timers
+   my $w = AnyEvent->timer (after => $seconds, cb => sub { ...  });
+   my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
+
+   print AnyEvent->now;  # prints current event loop time
+   print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
 
-   my $w = AnyEvent->timer (after => $seconds, cb => sub {
+   # POSIX signal
+   my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
+
+   # child process exit
+   my $w = AnyEvent->child (pid => $pid, cb => sub {
+      my ($pid, $status) = @_;
       ...
    });
 
+   # called when event loop idle (if applicable)
+   my $w = AnyEvent->idle (cb => sub { ... });
+
    my $w = AnyEvent->condvar; # stores whether a condition was flagged
-   $w->wait; # enters "main loop" till $condvar gets ->broadcast
-   $w->broadcast; # wake up current and all future wait's
+   $w->send; # wake up current and all future recv's
+   $w->recv; # enters "main loop" till $condvar gets ->send
+   # use a condvar in callback mode:
+   $w->cb (sub { $_[0]->recv });
+
+=head1 INTRODUCTION/TUTORIAL
+
+This manpage is mainly a reference manual. If you are interested
+in a tutorial or some gentle introduction, have a look at the
+L<AnyEvent::Intro> manpage.
+
+=head1 SUPPORT
+
+An FAQ document is available as L<AnyEvent::FAQ>.
+
+There also is a mailinglist for discussing all things AnyEvent, and an IRC
+channel, too.
+
+See the AnyEvent project page at the B<Schmorpforge Ta-Sa Software
+Repository>, at L<http://anyevent.schmorp.de>, for more info.
 
 =head1 WHY YOU SHOULD USE THIS MODULE (OR NOT)
 
@@ -29,11 +65,12 @@
 policy> and AnyEvent is I<small and efficient>.
 
 First and foremost, I<AnyEvent is not an event model> itself, it only
-interfaces to whatever event model the main program happens to use in a
+interfaces to whatever event model the main program happens to use, in a
 pragmatic way. For event models and certain classes of immortals alike,
 the statement "there can only be one" is a bitter reality: In general,
 only one event loop can be active at the same time in a process. AnyEvent
-helps hiding the differences between those event loops.
+cannot change this, but it can hide the differences between those event
+loops.
 
 The goal of AnyEvent is to offer module authors the ability to do event
 programming (waiting for I/O or timer events) without subscribing to a
@@ -43,50 +80,55 @@
 
 For modules like POE or IO::Async (which is a total misnomer as it is
 actually doing all I/O I<synchronously>...), using them in your module is
-like joining a cult: After you joined, you are dependent on them and you
-cannot use anything else, as it is simply incompatible to everything that
-isn't itself. What's worse, all the potential users of your module are
-I<also> forced to use the same event loop you use.
+like joining a cult: After you join, you are dependent on them and you
+cannot use anything else, as they are simply incompatible to everything
+that isn't them. What's worse, all the potential users of your
+module are I<also> forced to use the same event loop you use.
 
 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
 fine. AnyEvent + Tk works fine etc. etc. but none of these work together
-with the rest: POE + IO::Async? no go. Tk + Event? no go. Again: if
-your module uses one of those, every user of your module has to use it,
-too. But if your module uses AnyEvent, it works transparently with all
-event models it supports (including stuff like POE and IO::Async, as long
-as those use one of the supported event loops. It is trivial to add new
-event loops to AnyEvent, too, so it is future-proof).
+with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
+uses one of those, every user of your module has to use it, too. But if
+your module uses AnyEvent, it works transparently with all event models it
+supports (including stuff like IO::Async, as long as those use one of the
+supported event loops. It is easy to add new event loops to AnyEvent, too,
+so it is future-proof).
 
 In addition to being free of having to use I<the one and only true event
 model>, AnyEvent also is free of bloat and policy: with POE or similar
-modules, you get an enourmous amount of code and strict rules you have to
-follow. AnyEvent, on the other hand, is lean and up to the point, by only
+modules, you get an enormous amount of code and strict rules you have to
+follow. AnyEvent, on the other hand, is lean and to the point, by only
 offering the functionality that is necessary, in as thin as a wrapper as
 technically possible.
 
-Of course, if you want lots of policy (this can arguably be somewhat
+Of course, AnyEvent comes with a big (and fully optional!) toolbox
+of useful functionality, such as an asynchronous DNS resolver, 100%
+non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
+such as Windows) and lots of real-world knowledge and workarounds for
+platform bugs and differences.
+
+Now, if you I<do want> lots of policy (this can arguably be somewhat
 useful) and you want to force your users to use the one and only event
 model, you should I<not> use this module.
 
-
 =head1 DESCRIPTION
 
-L<AnyEvent> provides an identical interface to multiple event loops. This
-allows module authors to utilise an event loop without forcing module
-users to use the same event loop (as only a single event loop can coexist
-peacefully at any one time).
+L<AnyEvent> provides a uniform interface to various event loops. This
+allows module authors to use event loop functionality without forcing
+module users to use a specific event loop implementation (since more
+than one event loop cannot coexist peacefully).
 
 The interface itself is vaguely similar, but not identical to the L<Event>
 module.
 
 During the first call of any watcher-creation method, the module tries
 to detect the currently loaded event loop by probing whether one of the
-following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
-L<Event>, L<Glib>, L<Tk>. The first one found is used. If none are found,
-the module tries to load these modules in the stated order. The first one
-that can be successfully loaded will be used. If, after this, still none
-could be found, AnyEvent will fall back to a pure-perl event loop, which
-is not very efficient, but should work everywhere.
+following modules is already loaded: L<EV>, L<AnyEvent::Loop>,
+L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>. The first one
+found is used. If none are detected, the module tries to load the first
+four modules in the order given; but note that if L<EV> is not
+available, the pure-perl L<AnyEvent::Loop> should always work, so
+the other two are not normally tried.
 
 Because AnyEvent first checks for modules that are already loaded, loading
 an event model explicitly before first using AnyEvent will likely make
@@ -98,25 +140,32 @@
    # .. AnyEvent will likely default to Tk
 
 The I<likely> means that, if any module loads another event model and
-starts using it, all bets are off. Maybe you should tell their authors to
-use AnyEvent so their modules work together with others seamlessly...
-
-The pure-perl implementation of AnyEvent is called
-C<AnyEvent::Impl::Perl>. Like other event modules you can load it
-explicitly.
+starts using it, all bets are off - this case should be very rare though,
+as very few modules hardcode event loops without announcing this very
+loudly.
+
+The pure-perl implementation of AnyEvent is called C<AnyEvent::Loop>. Like
+other event modules you can load it explicitly and enjoy the high
+availability of that event loop :)
 
 =head1 WATCHERS
 
 AnyEvent has the central concept of a I<watcher>, which is an object that
 stores relevant data for each kind of event you are waiting for, such as
-the callback to call, the filehandle to watch, etc.
+the callback to call, the file handle to watch, etc.
 
 These watchers are normal Perl objects with normal Perl lifetime. After
 creating a watcher it will immediately "watch" for events and invoke the
 callback when the event occurs (of course, only when the event model
 is in control).
 
-To disable the watcher you have to destroy it (e.g. by setting the
+Note that B<callbacks must not permanently change global variables>
+potentially in use by the event loop (such as C<$_> or C<$[>) and that B<<
+callbacks must not C<die> >>. The former is good programming practice in
+Perl and the latter stems from the fact that exception handling differs
+widely between event loops.
+
+To disable a watcher you have to destroy it (e.g. by setting the
 variable you store it in to C<undef> or otherwise deleting all references
 to it).
 
@@ -125,41 +174,55 @@
 Many watchers either are used with "recursion" (repeating timers for
 example), or need to refer to their watcher object in other ways.
 
-An any way to achieve that is this pattern:
+One way to achieve that is this pattern:
 
-  my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
-     # you can use $w here, for example to undef it
-     undef $w;
-  });
+   my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
+      # you can use $w here, for example to undef it
+      undef $w;
+   });
 
 Note that C<my $w; $w => combination. This is necessary because in Perl,
 my variables are only visible after the statement in which they are
 declared.
 
-=head2 IO WATCHERS
+=head2 I/O WATCHERS
+
+   $w = AnyEvent->io (
+      fh   => <filehandle_or_fileno>,
+      poll => <"r" or "w">,
+      cb   => <callback>,
+   );
 
 You can create an I/O watcher by calling the C<< AnyEvent->io >> method
 with the following mandatory key-value pairs as arguments:
 
-C<fh> the Perl I<file handle> (I<not> file descriptor) to watch for
-events. C<poll> must be a string that is either C<r> or C<w>, which
-creates a watcher waiting for "r"eadable or "w"ritable events,
-respectively. C<cb> is the callback to invoke each time the file handle
-becomes ready.
+C<fh> is the Perl I<file handle> (or a naked file descriptor) to watch
+for events (AnyEvent might or might not keep a reference to this file
+handle). Note that only file handles pointing to things for which
+non-blocking operation makes sense are allowed. This includes sockets,
+most character devices, pipes, fifos and so on, but not for example files
+or block devices.
+
+C<poll> must be a string that is either C<r> or C<w>, which creates a
+watcher waiting for "r"eadable or "w"ritable events, respectively.
+
+C<cb> is the callback to invoke each time the file handle becomes ready.
+
+Although the callback might get passed parameters, their value and
+presence is undefined and you cannot rely on them. Portable AnyEvent
+callbacks cannot use arguments passed to I/O watcher callbacks.
+
+The I/O watcher might use the underlying file descriptor or a copy of it.
+You must not close a file handle as long as any watcher is active on the
+underlying file descriptor.
 
-File handles will be kept alive, so as long as the watcher exists, the
-file handle exists, too.
-
-It is not allowed to close a file handle as long as any watcher is active
-on the underlying file descriptor.
-
-Some event loops issue spurious readyness notifications, so you should
+Some event loops issue spurious readiness notifications, so you should
 always use non-blocking calls when reading/writing from/to your file
 handles.
 
-Example:
+Example: wait for readability of STDIN, then read a line and disable the
+watcher.
 
-   # wait for readability of STDIN, then read a line and disable the watcher
    my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
       chomp (my $input = <STDIN>);
       warn "read: $input\n";
@@ -168,20 +231,37 @@
 
 =head2 TIME WATCHERS
 
+   $w = AnyEvent->timer (after => <seconds>, cb => <callback>);
+
+   $w = AnyEvent->timer (
+      after    => <fractional_seconds>,
+      interval => <fractional_seconds>,
+      cb       => <callback>,
+   );
+
 You can create a time watcher by calling the C<< AnyEvent->timer >>
 method with the following mandatory arguments:
 
 C<after> specifies after how many seconds (fractional values are
-supported) should the timer activate. C<cb> the callback to invoke in that
-case.
+supported) the callback should be invoked. C<cb> is the callback to invoke
+in that case.
 
-The timer callback will be invoked at most once: if you want a repeating
-timer you have to create a new watcher (this is a limitation by both Tk
-and Glib).
+Although the callback might get passed parameters, their value and
+presence is undefined and you cannot rely on them. Portable AnyEvent
+callbacks cannot use arguments passed to time watcher callbacks.
+
+The callback will normally be invoked only once. If you specify another
+parameter, C<interval>, as a strictly positive number (> 0), then the
+callback will be invoked regularly at that interval (in fractional
+seconds) after the first invocation. If C<interval> is specified with a
+false value, then it is treated as if it were not specified at all.
+
+The callback will be rescheduled before invoking the callback, but no
+attempt is made to avoid timer drift in most backends, so the interval is
+only approximate.
 
-Example:
+Example: fire an event after 7.7 seconds.
 
-   # fire an event after 7.7 seconds
    my $w = AnyEvent->timer (after => 7.7, cb => sub {
       warn "timeout\n";
    });
@@ -189,184 +269,783 @@
    # to cancel the timer:
    undef $w;
 
-Example 2:
-
-   # fire an event after 0.5 seconds, then roughly every second
-   my $w;
+Example 2: fire an event after 0.5 seconds, then roughly every second.
 
-   my $cb = sub {
-      # cancel the old timer while creating a new one
-      $w = AnyEvent->timer (after => 1, cb => $cb);
+   my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
+      warn "timeout\n";
    };
 
-   # start the "loop" by creating the first watcher
-   $w = AnyEvent->timer (after => 0.5, cb => $cb);
-
 =head3 TIMING ISSUES
 
 There are two ways to handle timers: based on real time (relative, "fire
 in 10 seconds") and based on wallclock time (absolute, "fire at 12
 o'clock").
 
-While most event loops expect timers to specified in a relative way, they use
-absolute time internally. This makes a difference when your clock "jumps",
-for example, when ntp decides to set your clock backwards from the wrong 2014-01-01 to
-2008-01-01, a watcher that you created to fire "after" a second might actually take
-six years to finally fire.
+While most event loops expect timers to specified in a relative way, they
+use absolute time internally. This makes a difference when your clock
+"jumps", for example, when ntp decides to set your clock backwards from
+the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to
+fire "after a second" might actually take six years to finally fire.
 
 AnyEvent cannot compensate for this. The only event loop that is conscious
-about these issues is L<EV>, which offers both relative (ev_timer) and
-absolute (ev_periodic) timers.
+of these issues is L<EV>, which offers both relative (ev_timer, based
+on true relative time) and absolute (ev_periodic, based on wallclock time)
+timers.
 
 AnyEvent always prefers relative timers, if available, matching the
 AnyEvent API.
 
+AnyEvent has two additional methods that return the "current time":
+
+=over 4
+
+=item AnyEvent->time
+
+This returns the "current wallclock time" as a fractional number of
+seconds since the Epoch (the same thing as C<time> or C<Time::HiRes::time>
+return, and the result is guaranteed to be compatible with those).
+
+It progresses independently of any event loop processing, i.e. each call
+will check the system clock, which usually gets updated frequently.
+
+=item AnyEvent->now
+
+This also returns the "current wallclock time", but unlike C<time>, above,
+this value might change only once per event loop iteration, depending on
+the event loop (most return the same time as C<time>, above). This is the
+time that AnyEvent's timers get scheduled against.
+
+I<In almost all cases (in all cases if you don't care), this is the
+function to call when you want to know the current time.>
+
+This function is also often faster then C<< AnyEvent->time >>, and
+thus the preferred method if you want some timestamp (for example,
+L<AnyEvent::Handle> uses this to update its activity timeouts).
+
+The rest of this section is only of relevance if you try to be very exact
+with your timing; you can skip it without a bad conscience.
+
+For a practical example of when these times differ, consider L<Event::Lib>
+and L<EV> and the following set-up:
+
+The event loop is running and has just invoked one of your callbacks at
+time=500 (assume no other callbacks delay processing). In your callback,
+you wait a second by executing C<sleep 1> (blocking the process for a
+second) and then (at time=501) you create a relative timer that fires
+after three seconds.
+
+With L<Event::Lib>, C<< AnyEvent->time >> and C<< AnyEvent->now >> will
+both return C<501>, because that is the current time, and the timer will
+be scheduled to fire at time=504 (C<501> + C<3>).
+
+With L<EV>, C<< AnyEvent->time >> returns C<501> (as that is the current
+time), but C<< AnyEvent->now >> returns C<500>, as that is the time the
+last event processing phase started. With L<EV>, your timer gets scheduled
+to run at time=503 (C<500> + C<3>).
+
+In one sense, L<Event::Lib> is more exact, as it uses the current time
+regardless of any delays introduced by event processing. However, most
+callbacks do not expect large delays in processing, so this causes a
+higher drift (and a lot more system calls to get the current time).
+
+In another sense, L<EV> is more exact, as your timer will be scheduled at
+the same time, regardless of how long event processing actually took.
+
+In either case, if you care (and in most cases, you don't), then you
+can get whatever behaviour you want with any event loop, by taking the
+difference between C<< AnyEvent->time >> and C<< AnyEvent->now >> into
+account.
+
+=item AnyEvent->now_update
+
+Some event loops (such as L<EV> or L<AnyEvent::Loop>) cache the current
+time for each loop iteration (see the discussion of L<< AnyEvent->now >>,
+above).
+
+When a callback runs for a long time (or when the process sleeps), then
+this "current" time will differ substantially from the real time, which
+might affect timers and time-outs.
+
+When this is the case, you can call this method, which will update the
+event loop's idea of "current time".
+
+A typical example would be a script in a web server (e.g. C<mod_perl>) -
+when mod_perl executes the script, then the event loop will have the wrong
+idea about the "current time" (being potentially far in the past, when the
+script ran the last time). In that case you should arrange a call to C<<
+AnyEvent->now_update >> each time the web server process wakes up again
+(e.g. at the start of your script, or in a handler).
+
+Note that updating the time I<might> cause some events to be handled.
+
+=back
+
 =head2 SIGNAL WATCHERS
 
+   $w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
+
 You can watch for signals using a signal watcher, C<signal> is the signal
-I<name> without any C<SIG> prefix, C<cb> is the Perl callback to
-be invoked whenever a signal occurs.
+I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
+callback to be invoked whenever a signal occurs.
 
-Multiple signals occurances can be clumped together into one callback
-invocation, and callback invocation will be synchronous. synchronous means
+Although the callback might get passed parameters, their value and
+presence is undefined and you cannot rely on them. Portable AnyEvent
+callbacks cannot use arguments passed to signal watcher callbacks.
+
+Multiple signal occurrences can be clumped together into one callback
+invocation, and callback invocation will be synchronous. Synchronous means
 that it might take a while until the signal gets handled by the process,
-but it is guarenteed not to interrupt any other callbacks.
+but it is guaranteed not to interrupt any other callbacks.
 
 The main advantage of using these watchers is that you can share a signal
-between multiple watchers.
+between multiple watchers, and AnyEvent will ensure that signals will not
+interrupt your program at bad times.
 
-This watcher might use C<%SIG>, so programs overwriting those signals
-directly will likely not work correctly.
+This watcher might use C<%SIG> (depending on the event loop used),
+so programs overwriting those signals directly will likely not work
+correctly.
 
 Example: exit on SIGINT
 
    my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
 
+=head3 Restart Behaviour
+
+While restart behaviour is up to the event loop implementation, most will
+not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
+pure perl implementation).
+
+=head3 Safe/Unsafe Signals
+
+Perl signals can be either "safe" (synchronous to opcode handling) or
+"unsafe" (asynchronous) - the former might get delayed indefinitely, the
+latter might corrupt your memory.
+
+AnyEvent signal handlers are, in addition, synchronous to the event loop,
+i.e. they will not interrupt your running perl program but will only be
+called as part of the normal event handling (just like timer, I/O etc.
+callbacks, too).
+
+=head3 Signal Races, Delays and Workarounds
+
+Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
+callbacks to signals in a generic way, which is a pity, as you cannot
+do race-free signal handling in perl, requiring C libraries for
+this. AnyEvent will try to do its best, which means in some cases,
+signals will be delayed. The maximum time a signal might be delayed is
+specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10 seconds). This
+variable can be changed only before the first signal watcher is created,
+and should be left alone otherwise. This variable determines how often
+AnyEvent polls for signals (in case a wake-up was missed). Higher values
+will cause fewer spurious wake-ups, which is better for power and CPU
+saving.
+
+All these problems can be avoided by installing the optional
+L<Async::Interrupt> module, which works with most event loops. It will not
+work with inherently broken event loops such as L<Event> or L<Event::Lib>
+(and not with L<POE> currently, as POE does its own workaround with
+one-second latency). For those, you just have to suffer the delays.
+
 =head2 CHILD PROCESS WATCHERS
 
-You can also watch on a child process exit and catch its exit status.
+   $w = AnyEvent->child (pid => <process id>, cb => <callback>);
 
-The child process is specified by the C<pid> argument (if set to C<0>, it
-watches for any child process exit). The watcher will trigger as often
-as status change for the child are received. This works by installing a
-signal handler for C<SIGCHLD>. The callback will be called with the pid
-and exit status (as returned by waitpid).
-
-Example: wait for pid 1333
-
-  my $w = AnyEvent->child (
-     pid => 1333,
-     cb  => sub {
-        my ($pid, $status) = @_;
-        warn "pid $pid exited with status $status";
-     },
-  );
+You can also watch for a child process exit and catch its exit status.
+
+The child process is specified by the C<pid> argument (on some backends,
+using C<0> watches for any child process exit, on others this will
+croak). The watcher will be triggered only when the child process has
+finished and an exit status is available, not on any trace events
+(stopped/continued).
+
+The callback will be called with the pid and exit status (as returned by
+waitpid), so unlike other watcher types, you I<can> rely on child watcher
+callback arguments.
+
+This watcher type works by installing a signal handler for C<SIGCHLD>,
+and since it cannot be shared, nothing else should use SIGCHLD or reap
+random child processes (waiting for specific child processes, e.g. inside
+C<system>, is just fine).
+
+There is a slight catch to child watchers, however: you usually start them
+I<after> the child process was created, and this means the process could
+have exited already (and no SIGCHLD will be sent anymore).
+
+Not all event models handle this correctly (neither POE nor IO::Async do,
+see their AnyEvent::Impl manpages for details), but even for event models
+that I<do> handle this correctly, they usually need to be loaded before
+the process exits (i.e. before you fork in the first place). AnyEvent's
+pure perl event loop handles all cases correctly regardless of when you
+start the watcher.
+
+This means you cannot create a child watcher as the very first
+thing in an AnyEvent program, you I<have> to create at least one
+watcher before you C<fork> the child (alternatively, you can call
+C<AnyEvent::detect>).
+
+As most event loops do not support waiting for child events, they will be
+emulated by AnyEvent in most cases, in which case the latency and race
+problems mentioned in the description of signal watchers apply.
+
+Example: fork a process and wait for it
+
+   my $done = AnyEvent->condvar;
+  
+   my $pid = fork or exit 5;
+  
+   my $w = AnyEvent->child (
+      pid => $pid,
+      cb  => sub {
+         my ($pid, $status) = @_;
+         warn "pid $pid exited with status $status";
+         $done->send;
+      },
+   );
+  
+   # do something else, then wait for process exit
+   $done->recv;
+
+=head2 IDLE WATCHERS
+
+   $w = AnyEvent->idle (cb => <callback>);
+
+This will repeatedly invoke the callback after the process becomes idle,
+until either the watcher is destroyed or new events have been detected.
+
+Idle watchers are useful when there is a need to do something, but it
+is not so important (or wise) to do it instantly. The callback will be
+invoked only when there is "nothing better to do", which is usually
+defined as "all outstanding events have been handled and no new events
+have been detected". That means that idle watchers ideally get invoked
+when the event loop has just polled for new events but none have been
+detected. Instead of blocking to wait for more events, the idle watchers
+will be invoked.
+
+Unfortunately, most event loops do not really support idle watchers (only
+EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
+will simply call the callback "from time to time".
+
+Example: read lines from STDIN, but only process them when the
+program is otherwise idle:
+
+   my @lines; # read data
+   my $idle_w;
+   my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
+      push @lines, scalar <STDIN>;
+
+      # start an idle watcher, if not already done
+      $idle_w ||= AnyEvent->idle (cb => sub {
+         # handle only one line, when there are lines left
+         if (my $line = shift @lines) {
+            print "handled when idle: $line";
+         } else {
+            # otherwise disable the idle watcher again
+            undef $idle_w;
+         }
+      });
+   });
 
 =head2 CONDITION VARIABLES
 
-Condition variables can be created by calling the C<< AnyEvent->condvar >>
-method without any arguments.
+   $cv = AnyEvent->condvar;
+
+   $cv->send (<list>);
+   my @res = $cv->recv;
+
+If you are familiar with some event loops you will know that all of them
+require you to run some blocking "loop", "run" or similar function that
+will actively watch for new events and call your callbacks.
+
+AnyEvent is slightly different: it expects somebody else to run the event
+loop and will only block when necessary (usually when told by the user).
+
+The tool to do that is called a "condition variable", so called because
+they represent a condition that must become true.
 
-A condition variable waits for a condition - precisely that the C<<
-->broadcast >> method has been called.
+Now is probably a good time to look at the examples further below.
 
-They are very useful to signal that a condition has been fulfilled, for
-example, if you write a module that does asynchronous http requests,
+Condition variables can be created by calling the C<< AnyEvent->condvar
+>> method, usually without arguments. The only argument pair allowed is
+C<cb>, which specifies a callback to be called when the condition variable
+becomes true, with the condition variable as the first argument (but not
+the results).
+
+After creation, the condition variable is "false" until it becomes "true"
+by calling the C<send> method (or calling the condition variable as if it
+were a callback, read about the caveats in the description for the C<<
+->send >> method).
+
+Since condition variables are the most complex part of the AnyEvent API, here are
+some different mental models of what they are - pick the ones you can connect to:
+
+=over 4
+
+=item * Condition variables are like callbacks - you can call them (and pass them instead
+of callbacks). Unlike callbacks however, you can also wait for them to be called.
+
+=item * Condition variables are signals - one side can emit or send them,
+the other side can wait for them, or install a handler that is called when
+the signal fires.
+
+=item * Condition variables are like "Merge Points" - points in your program
+where you merge multiple independent results/control flows into one.
+
+=item * Condition variables represent a transaction - functions that start
+some kind of transaction can return them, leaving the caller the choice
+between waiting in a blocking fashion, or setting a callback.
+
+=item * Condition variables represent future values, or promises to deliver
+some result, long before the result is available.
+
+=back
+
+Condition variables are very useful to signal that something has finished,
+for example, if you write a module that does asynchronous http requests,
 then a condition variable would be the ideal candidate to signal the
-availability of results.
+availability of results. The user can either act when the callback is
+called or can synchronously C<< ->recv >> for the results.
 
-You can also use condition variables to block your main program until
-an event occurs - for example, you could C<< ->wait >> in your main
-program until the user clicks the Quit button in your app, which would C<<
-->broadcast >> the "quit" event.
+You can also use them to simulate traditional event loops - for example,
+you can block your main program until an event occurs - for example, you
+could C<< ->recv >> in your main program until the user clicks the Quit
+button of your app, which would C<< ->send >> the "quit" event.
 
 Note that condition variables recurse into the event loop - if you have
-two pirces of code that call C<< ->wait >> in a round-robbin fashion, you
+two pieces of code that call C<< ->recv >> in a round-robin fashion, you
 lose. Therefore, condition variables are good to export to your caller, but
 you should avoid making a blocking wait yourself, at least in callbacks,
 as this asks for trouble.
 
-This object has two methods:
+Condition variables are represented by hash refs in perl, and the keys
+used by AnyEvent itself are all named C<_ae_XXX> to make subclassing
+easy (it is often useful to build your own transaction class on top of
+AnyEvent). To subclass, use C<AnyEvent::CondVar> as base class and call
+its C<new> method in your own C<new> method.
+
+There are two "sides" to a condition variable - the "producer side" which
+eventually calls C<< -> send >>, and the "consumer side", which waits
+for the send to occur.
+
+Example: wait for a timer.
+
+   # condition: "wait till the timer is fired"
+   my $timer_fired = AnyEvent->condvar;
+
+   # create the timer - we could wait for, say
+   # a handle becomign ready, or even an
+   # AnyEvent::HTTP request to finish, but
+   # in this case, we simply use a timer:
+   my $w = AnyEvent->timer (
+      after => 1,
+      cb    => sub { $timer_fired->send },
+   );
+
+   # this "blocks" (while handling events) till the callback
+   # calls ->send
+   $timer_fired->recv;
+
+Example: wait for a timer, but take advantage of the fact that condition
+variables are also callable directly.
+
+   my $done = AnyEvent->condvar;
+   my $delay = AnyEvent->timer (after => 5, cb => $done);
+   $done->recv;
+
+Example: Imagine an API that returns a condvar and doesn't support
+callbacks. This is how you make a synchronous call, for example from
+the main program:
+
+   use AnyEvent::CouchDB;
+
+   ...
+
+   my @info = $couchdb->info->recv;
+
+And this is how you would just set a callback to be called whenever the
+results are available:
+
+   $couchdb->info->cb (sub {
+      my @info = $_[0]->recv;
+   });
+
+=head3 METHODS FOR PRODUCERS
+
+These methods should only be used by the producing side, i.e. the
+code/module that eventually sends the signal. Note that it is also
+the producer side which creates the condvar in most cases, but it isn't
+uncommon for the consumer to create it as well.
 
 =over 4
 
-=item $cv->wait
+=item $cv->send (...)
+
+Flag the condition as ready - a running C<< ->recv >> and all further
+calls to C<recv> will (eventually) return after this method has been
+called. If nobody is waiting the send will be remembered.
+
+If a callback has been set on the condition variable, it is called
+immediately from within send.
+
+Any arguments passed to the C<send> call will be returned by all
+future C<< ->recv >> calls.
+
+Condition variables are overloaded so one can call them directly (as if
+they were a code reference). Calling them directly is the same as calling
+C<send>.
+
+=item $cv->croak ($error)
+
+Similar to send, but causes all calls to C<< ->recv >> to invoke
+C<Carp::croak> with the given error message/object/scalar.
+
+This can be used to signal any errors to the condition variable
+user/consumer. Doing it this way instead of calling C<croak> directly
+delays the error detection, but has the overwhelming advantage that it
+diagnoses the error at the place where the result is expected, and not
+deep in some event callback with no connection to the actual code causing
+the problem.
+
+=item $cv->begin ([group callback])
+
+=item $cv->end
+
+These two methods can be used to combine many transactions/events into
+one. For example, a function that pings many hosts in parallel might want
+to use a condition variable for the whole process.
+
+Every call to C<< ->begin >> will increment a counter, and every call to
+C<< ->end >> will decrement it.  If the counter reaches C<0> in C<< ->end
+>>, the (last) callback passed to C<begin> will be executed, passing the
+condvar as first argument. That callback is I<supposed> to call C<< ->send
+>>, but that is not required. If no group callback was set, C<send> will
+be called without any arguments.
+
+You can think of C<< $cv->send >> giving you an OR condition (one call
+sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
+condition (all C<begin> calls must be C<end>'ed before the condvar sends).
+
+Let's start with a simple example: you have two I/O watchers (for example,
+STDOUT and STDERR for a program), and you want to wait for both streams to
+close before activating a condvar:
+
+   my $cv = AnyEvent->condvar;
+
+   $cv->begin; # first watcher
+   my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
+      defined sysread $fh1, my $buf, 4096
+         or $cv->end;
+   });
+
+   $cv->begin; # second watcher
+   my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
+      defined sysread $fh2, my $buf, 4096
+         or $cv->end;
+   });
+
+   $cv->recv;
+
+This works because for every event source (EOF on file handle), there is
+one call to C<begin>, so the condvar waits for all calls to C<end> before
+sending.
+
+The ping example mentioned above is slightly more complicated, as the
+there are results to be passwd back, and the number of tasks that are
+begun can potentially be zero:
+
+   my $cv = AnyEvent->condvar;
+
+   my %result;
+   $cv->begin (sub { shift->send (\%result) });
+
+   for my $host (@list_of_hosts) {
+      $cv->begin;
+      ping_host_then_call_callback $host, sub {
+         $result{$host} = ...;
+         $cv->end;
+      };
+   }
+
+   $cv->end;
+
+This code fragment supposedly pings a number of hosts and calls
+C<send> after results for all then have have been gathered - in any
+order. To achieve this, the code issues a call to C<begin> when it starts
+each ping request and calls C<end> when it has received some result for
+it. Since C<begin> and C<end> only maintain a counter, the order in which
+results arrive is not relevant.
+
+There is an additional bracketing call to C<begin> and C<end> outside the
+loop, which serves two important purposes: first, it sets the callback
+to be called once the counter reaches C<0>, and second, it ensures that
+C<send> is called even when C<no> hosts are being pinged (the loop
+doesn't execute once).
+
+This is the general pattern when you "fan out" into multiple (but
+potentially zero) subrequests: use an outer C<begin>/C<end> pair to set
+the callback and ensure C<end> is called at least once, and then, for each
+subrequest you start, call C<begin> and for each subrequest you finish,
+call C<end>.
+
+=back
+
+=head3 METHODS FOR CONSUMERS
+
+These methods should only be used by the consuming side, i.e. the
+code awaits the condition.
+
+=over 4
 
-Wait (blocking if necessary) until the C<< ->broadcast >> method has been
-called on c<$cv>, while servicing other watchers normally.
+=item $cv->recv
 
-You can only wait once on a condition - additional calls will return
-immediately.
+Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
+>> methods have been called on C<$cv>, while servicing other watchers
+normally.
+
+You can only wait once on a condition - additional calls are valid but
+will return immediately.
+
+If an error condition has been set by calling C<< ->croak >>, then this
+function will call C<croak>.
+
+In list context, all parameters passed to C<send> will be returned,
+in scalar context only the first one will be returned.
+
+Note that doing a blocking wait in a callback is not supported by any
+event loop, that is, recursive invocation of a blocking C<< ->recv
+>> is not allowed, and the C<recv> call will C<croak> if such a
+condition is detected. This condition can be slightly loosened by using
+L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
+any thread that doesn't run the event loop itself.
 
 Not all event models support a blocking wait - some die in that case
 (programs might want to do that to stay interactive), so I<if you are
-using this from a module, never require a blocking wait>, but let the
+using this from a module, never require a blocking wait>. Instead, let the
 caller decide whether the call will block or not (for example, by coupling
 condition variables with some kind of request results and supporting
 callbacks so the caller knows that getting the result will not block,
-while still suppporting blocking waits if the caller so desires).
+while still supporting blocking waits if the caller so desires).
 
-Another reason I<never> to C<< ->wait >> in a module is that you cannot
-sensibly have two C<< ->wait >>'s in parallel, as that would require
-multiple interpreters or coroutines/threads, none of which C<AnyEvent>
-can supply (the coroutine-aware backends L<AnyEvent::Impl::CoroEV> and
-L<AnyEvent::Impl::CoroEvent> explicitly support concurrent C<< ->wait >>'s
-from different coroutines, however).
-
-=item $cv->broadcast
-
-Flag the condition as ready - a running C<< ->wait >> and all further
-calls to C<wait> will (eventually) return after this method has been
-called. If nobody is waiting the broadcast will be remembered..
+You can ensure that C<< ->recv >> never blocks by setting a callback and
+only calling C<< ->recv >> from within that callback (or at a later
+time). This will work even when the event loop does not support blocking
+waits otherwise.
+
+=item $bool = $cv->ready
+
+Returns true when the condition is "true", i.e. whether C<send> or
+C<croak> have been called.
+
+=item $cb = $cv->cb ($cb->($cv))
+
+This is a mutator function that returns the callback set and optionally
+replaces it before doing so.
+
+The callback will be called when the condition becomes "true", i.e. when
+C<send> or C<croak> are called, with the only argument being the
+condition variable itself. If the condition is already true, the
+callback is called immediately when it is set. Calling C<recv> inside
+the callback or at any later time is guaranteed not to block.
 
 =back
 
-Example:
+=head1 SUPPORTED EVENT LOOPS/BACKENDS
 
-   # wait till the result is ready
-   my $result_ready = AnyEvent->condvar;
+The available backend classes are (every class has its own manpage):
 
-   # do something such as adding a timer
-   # or socket watcher the calls $result_ready->broadcast
-   # when the "result" is ready.
-   # in this case, we simply use a timer:
-   my $w = AnyEvent->timer (
-      after => 1,
-      cb    => sub { $result_ready->broadcast },
-   );
+=over 4
+
+=item Backends that are autoprobed when no other event loop can be found.
+
+EV is the preferred backend when no other event loop seems to be in
+use. If EV is not installed, then AnyEvent will fall back to its own
+pure-perl implementation, which is available everywhere as it comes with
+AnyEvent itself.
+
+   AnyEvent::Impl::EV        based on EV (interface to libev, best choice).
+   AnyEvent::Impl::Perl      pure-perl AnyEvent::Loop, fast and portable.
+
+=item Backends that are transparently being picked up when they are used.
+
+These will be used if they are already loaded when the first watcher
+is created, in which case it is assumed that the application is using
+them. This means that AnyEvent will automatically pick the right backend
+when the main program loads an event module before anything starts to
+create watchers. Nothing special needs to be done by the main program.
+
+   AnyEvent::Impl::Event     based on Event, very stable, few glitches.
+   AnyEvent::Impl::Glib      based on Glib, slow but very stable.
+   AnyEvent::Impl::Tk        based on Tk, very broken.
+   AnyEvent::Impl::EventLib  based on Event::Lib, leaks memory and worse.
+   AnyEvent::Impl::POE       based on POE, very slow, some limitations.
+   AnyEvent::Impl::Irssi     used when running within irssi.
+   AnyEvent::Impl::IOAsync   based on IO::Async.
+   AnyEvent::Impl::Cocoa     based on Cocoa::EventLoop.
+   AnyEvent::Impl::FLTK2     based on FLTK (fltk 2 binding).
 
-   # this "blocks" (while handling events) till the watcher
-   # calls broadcast
-   $result_ready->wait;
+=item Backends with special needs.
+
+Qt requires the Qt::Application to be instantiated first, but will
+otherwise be picked up automatically. As long as the main program
+instantiates the application before any AnyEvent watchers are created,
+everything should just work.
+
+   AnyEvent::Impl::Qt        based on Qt.
+
+=item Event loops that are indirectly supported via other backends.
+
+Some event loops can be supported via other modules:
+
+There is no direct support for WxWidgets (L<Wx>) or L<Prima>.
+
+B<WxWidgets> has no support for watching file handles. However, you can
+use WxWidgets through the POE adaptor, as POE has a Wx backend that simply
+polls 20 times per second, which was considered to be too horrible to even
+consider for AnyEvent.
+
+B<Prima> is not supported as nobody seems to be using it, but it has a POE
+backend, so it can be supported through POE.
+
+AnyEvent knows about both L<Prima> and L<Wx>, however, and will try to
+load L<POE> when detecting them, in the hope that POE will pick them up,
+in which case everything will be automatic.
+
+=back
 
 =head1 GLOBAL VARIABLES AND FUNCTIONS
 
+These are not normally required to use AnyEvent, but can be useful to
+write AnyEvent extension modules.
+
 =over 4
 
 =item $AnyEvent::MODEL
 
-Contains C<undef> until the first watcher is being created. Then it
-contains the event model that is being used, which is the name of the
-Perl class implementing the model. This class is usually one of the
-C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
-AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
-
-The known classes so far are:
-
-   AnyEvent::Impl::CoroEV    based on Coro::EV, best choice.
-   AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
-   AnyEvent::Impl::EV        based on EV (an interface to libev, also best choice).
-   AnyEvent::Impl::Event     based on Event, also second best choice :)
-   AnyEvent::Impl::Glib      based on Glib, third-best choice.
-   AnyEvent::Impl::Tk        based on Tk, very bad choice.
-   AnyEvent::Impl::Perl      pure-perl implementation, inefficient but portable.
+Contains C<undef> until the first watcher is being created, before the
+backend has been autodetected.
+
+Afterwards it contains the event model that is being used, which is the
+name of the Perl class implementing the model. This class is usually one
+of the C<AnyEvent::Impl::xxx> modules, but can be any other class in the
+case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
+will be C<urxvt::anyevent>).
 
 =item AnyEvent::detect
 
 Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
 if necessary. You should only call this function right before you would
 have created an AnyEvent watcher anyway, that is, as late as possible at
-runtime.
+runtime, and not e.g. during initialisation of your module.
+
+If you need to do some initialisation before AnyEvent watchers are
+created, use C<post_detect>.
+
+=item $guard = AnyEvent::post_detect { BLOCK }
+
+Arranges for the code block to be executed as soon as the event model is
+autodetected (or immediately if that has already happened).
+
+The block will be executed I<after> the actual backend has been detected
+(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
+created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
+other initialisations - see the sources of L<AnyEvent::Strict> or
+L<AnyEvent::AIO> to see how this is used.
+
+The most common usage is to create some global watchers, without forcing
+event module detection too early, for example, L<AnyEvent::AIO> creates
+and installs the global L<IO::AIO> watcher in a C<post_detect> block to
+avoid autodetecting the event module at load time.
+
+If called in scalar or list context, then it creates and returns an object
+that automatically removes the callback again when it is destroyed (or
+C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
+a case where this is useful.
+
+Example: Create a watcher for the IO::AIO module and store it in
+C<$WATCHER>, but do so only do so after the event loop is initialised.
+
+   our WATCHER;
+
+   my $guard = AnyEvent::post_detect {
+      $WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
+   };
+
+   # the ||= is important in case post_detect immediately runs the block,
+   # as to not clobber the newly-created watcher. assigning both watcher and
+   # post_detect guard to the same variable has the advantage of users being
+   # able to just C<undef $WATCHER> if the watcher causes them grief.
+
+   $WATCHER ||= $guard;
+
+=item @AnyEvent::post_detect
+
+If there are any code references in this array (you can C<push> to it
+before or after loading AnyEvent), then they will be called directly
+after the event loop has been chosen.
+
+You should check C<$AnyEvent::MODEL> before adding to this array, though:
+if it is defined then the event loop has already been detected, and the
+array will be ignored.
+
+Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
+it, as it takes care of these details.
+
+This variable is mainly useful for modules that can do something useful
+when AnyEvent is used and thus want to know when it is initialised, but do
+not need to even load it by default. This array provides the means to hook
+into AnyEvent passively, without loading it.
+
+Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
+together, you could put this into Coro (this is the actual code used by
+Coro to accomplish this):
+
+   if (defined $AnyEvent::MODEL) {
+      # AnyEvent already initialised, so load Coro::AnyEvent
+      require Coro::AnyEvent;
+   } else {
+      # AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
+      # as soon as it is
+      push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
+   }
+
+=item AnyEvent::postpone { BLOCK }
+
+Arranges for the block to be executed as soon as possible, but not before
+the call itself returns. In practise, the block will be executed just
+before the event loop polls for new events, or shortly afterwards.
+
+This function never returns anything (to make the C<return postpone { ...
+}> idiom more useful.
+
+To understand the usefulness of this function, consider a function that
+asynchronously does something for you and returns some transaction
+object or guard to let you cancel the operation. For example,
+C<AnyEvent::Socket::tcp_connect>:
+
+   # start a conenction attempt unless one is active
+   $self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
+      delete $self->{connect_guard};
+      ...
+   };
+
+Imagine that this function could instantly call the callback, for
+example, because it detects an obvious error such as a negative port
+number. Invoking the callback before the function returns causes problems
+however: the callback will be called and will try to delete the guard
+object. But since the function hasn't returned yet, there is nothing to
+delete. When the function eventually returns it will assign the guard
+object to C<< $self->{connect_guard} >>, where it will likely never be
+deleted, so the program thinks it is still trying to connect.
+
+This is where C<AnyEvent::postpone> should be used. Instead of calling the
+callback directly on error:
+
+   $cb->(undef), return # signal error to callback, BAD!
+      if $some_error_condition;
+
+It should use C<postpone>:
+
+   AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
+      if $some_error_condition;
 
 =back
 
@@ -380,161 +1059,652 @@
 by calling AnyEvent in your module body you force the user of your module
 to load the event module first.
 
-Never call C<< ->wait >> on a condition variable unless you I<know> that
-the C<< ->broadcast >> method has been called on it already. This is
+Never call C<< ->recv >> on a condition variable unless you I<know> that
+the C<< ->send >> method has been called on it already. This is
 because it will stall the whole program, and the whole point of using
 events is to stay interactive.
 
-It is fine, however, to call C<< ->wait >> when the user of your module
+It is fine, however, to call C<< ->recv >> when the user of your module
 requests it (i.e. if you create a http request object ad have a method
-called C<results> that returns the results, it should call C<< ->wait >>
-freely, as the user of your module knows what she is doing. always).
+called C<results> that returns the results, it may call C<< ->recv >>
+freely, as the user of your module knows what she is doing. Always).
 
 =head1 WHAT TO DO IN THE MAIN PROGRAM
 
 There will always be a single main program - the only place that should
 dictate which event model to use.
 
-If it doesn't care, it can just "use AnyEvent" and use it itself, or not
-do anything special (it does not need to be event-based) and let AnyEvent
-decide which implementation to chose if some module relies on it.
+If the program is not event-based, it need not do anything special, even
+when it depends on a module that uses an AnyEvent. If the program itself
+uses AnyEvent, but does not care which event loop is used, all it needs
+to do is C<use AnyEvent>. In either case, AnyEvent will choose the best
+available loop implementation.
 
-If the main program relies on a specific event model. For example, in
-Gtk2 programs you have to rely on the Glib module. You should load the
+If the main program relies on a specific event model - for example, in
+Gtk2 programs you have to rely on the Glib module - you should load the
 event module before loading AnyEvent or any module that uses it: generally
 speaking, you should load it as early as possible. The reason is that
 modules might create watchers when they are loaded, and AnyEvent will
 decide on the event model to use as soon as it creates watchers, and it
-might chose the wrong one unless you load the correct one yourself.
+might choose the wrong one unless you load the correct one yourself.
+
+You can chose to use a pure-perl implementation by loading the
+C<AnyEvent::Loop> module, which gives you similar behaviour
+everywhere, but letting AnyEvent chose the model is generally better.
+
+=head2 MAINLOOP EMULATION
+
+Sometimes (often for short test scripts, or even standalone programs who
+only want to use AnyEvent), you do not want to run a specific event loop.
+
+In that case, you can use a condition variable like this:
+
+   AnyEvent->condvar->recv;
+
+This has the effect of entering the event loop and looping forever.
+
+Note that usually your program has some exit condition, in which case
+it is better to use the "traditional" approach of storing a condition
+variable somewhere, waiting for it, and sending it when the program should
+exit cleanly.
+
+
+=head1 OTHER MODULES
+
+The following is a non-exhaustive list of additional modules that use
+AnyEvent as a client and can therefore be mixed easily with other AnyEvent
+modules and other event loops in the same program. Some of the modules
+come as part of AnyEvent, the others are available via CPAN.
+
+=over 4
+
+=item L<AnyEvent::Util>
+
+Contains various utility functions that replace often-used blocking
+functions such as C<inet_aton> with event/callback-based versions.
+
+=item L<AnyEvent::Socket>
+
+Provides various utility functions for (internet protocol) sockets,
+addresses and name resolution. Also functions to create non-blocking tcp
+connections or tcp servers, with IPv6 and SRV record support and more.
 
-You can chose to use a rather inefficient pure-perl implementation by
-loading the C<AnyEvent::Impl::Perl> module, which gives you similar
-behaviour everywhere, but letting AnyEvent chose is generally better.
+=item L<AnyEvent::Handle>
+
+Provide read and write buffers, manages watchers for reads and writes,
+supports raw and formatted I/O, I/O queued and fully transparent and
+non-blocking SSL/TLS (via L<AnyEvent::TLS>).
+
+=item L<AnyEvent::DNS>
+
+Provides rich asynchronous DNS resolver capabilities.
+
+=item L<AnyEvent::HTTP>, L<AnyEvent::IRC>, L<AnyEvent::XMPP>, L<AnyEvent::GPSD>, L<AnyEvent::IGS>, L<AnyEvent::FCP>
+
+Implement event-based interfaces to the protocols of the same name (for
+the curious, IGS is the International Go Server and FCP is the Freenet
+Client Protocol).
+
+=item L<AnyEvent::Handle::UDP>
+
+Here be danger!
+
+As Pauli would put it, "Not only is it not right, it's not even wrong!" -
+there are so many things wrong with AnyEvent::Handle::UDP, most notably
+its use of a stream-based API with a protocol that isn't streamable, that
+the only way to improve it is to delete it.
+
+It features data corruption (but typically only under load) and general
+confusion. On top, the author is not only clueless about UDP but also
+fact-resistant - some gems of his understanding: "connect doesn't work
+with UDP", "UDP packets are not IP packets", "UDP only has datagrams, not
+packets", "I don't need to implement proper error checking as UDP doesn't
+support error checking" and so on - he doesn't even understand what's
+wrong with his module when it is explained to him.
+
+=item L<AnyEvent::DBI>
+
+Executes L<DBI> requests asynchronously in a proxy process for you,
+notifying you in an event-based way when the operation is finished.
+
+=item L<AnyEvent::AIO>
+
+Truly asynchronous (as opposed to non-blocking) I/O, should be in the
+toolbox of every event programmer. AnyEvent::AIO transparently fuses
+L<IO::AIO> and AnyEvent together, giving AnyEvent access to event-based
+file I/O, and much more.
+
+=item L<AnyEvent::HTTPD>
+
+A simple embedded webserver.
+
+=item L<AnyEvent::FastPing>
+
+The fastest ping in the west.
+
+=item L<Coro>
+
+Has special support for AnyEvent via L<Coro::AnyEvent>.
+
+=back
 
 =cut
 
 package AnyEvent;
 
-no warnings;
-use strict;
+# basically a tuned-down version of common::sense
+sub common_sense {
+   # from common:.sense 3.4
+   ${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00";
+   # use strict vars subs - NO UTF-8, as Util.pm doesn't like this atm. (uts46data.pl)
+   $^H |= 0x00000600;
+}
+
+BEGIN { AnyEvent::common_sense }
 
-use Carp;
+use Carp ();
 
-our $VERSION = '3.12';
+our $VERSION = '5.34';
 our $MODEL;
 
-our $AUTOLOAD;
 our @ISA;
 
-our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
-
 our @REGISTRY;
 
-my @models = (
-   [Coro::EV::             => AnyEvent::Impl::CoroEV::],
-   [Coro::Event::          => AnyEvent::Impl::CoroEvent::],
-   [EV::                   => AnyEvent::Impl::EV::],
-   [Event::                => AnyEvent::Impl::Event::],
-   [Glib::                 => AnyEvent::Impl::Glib::],
-   [Tk::                   => AnyEvent::Impl::Tk::],
-   [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
+our $VERBOSE;
+
+BEGIN {
+   require "AnyEvent/constants.pl";
+
+   eval "sub TAINT (){" . (${^TAINT}*1) . "}";
+
+   delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
+      if ${^TAINT};
+
+   $VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
+
+}
+
+our $MAX_SIGNAL_LATENCY = 10;
+
+our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
+
+{
+   my $idx;
+   $PROTOCOL{$_} = ++$idx
+      for reverse split /\s*,\s*/,
+             $ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
+}
+
+our @post_detect;
+
+sub post_detect(&) {
+   my ($cb) = @_;
+
+   push @post_detect, $cb;
+
+   defined wantarray
+      ? bless \$cb, "AnyEvent::Util::postdetect"
+      : ()
+}
+
+sub AnyEvent::Util::postdetect::DESTROY {
+   @post_detect = grep $_ != ${$_[0]}, @post_detect;
+}
+
+our $POSTPONE_W;
+our @POSTPONE;
+
+sub _postpone_exec {
+   undef $POSTPONE_W;
+
+   &{ shift @POSTPONE }
+      while @POSTPONE;
+}
+
+sub postpone(&) {
+   push @POSTPONE, shift;
+
+   $POSTPONE_W ||= AE::timer (0, 0, \&_postpone_exec);
+
+   ()
+}
+
+our @models = (
+   [EV::                   => AnyEvent::Impl::EV::   , 1],
+   [AnyEvent::Loop::       => AnyEvent::Impl::Perl:: , 1],
+   # everything below here will not (normally) be autoprobed
+   # as the pure perl backend should work everywhere
+   # and is usually faster
+   [Event::                => AnyEvent::Impl::Event::, 1],
+   [Glib::                 => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
+   [Event::Lib::           => AnyEvent::Impl::EventLib::], # too buggy
+   [Irssi::                => AnyEvent::Impl::Irssi::],    # Irssi has a bogus "Event" package
+   [Tk::                   => AnyEvent::Impl::Tk::],       # crashes with many handles
+   [Qt::                   => AnyEvent::Impl::Qt::],       # requires special main program
+   [POE::Kernel::          => AnyEvent::Impl::POE::],      # lasciate ogni speranza
+   [Wx::                   => AnyEvent::Impl::POE::],
+   [Prima::                => AnyEvent::Impl::POE::],
+   [IO::Async::Loop::      => AnyEvent::Impl::IOAsync::],  # a bitch to autodetect
+   [Cocoa::EventLoop::     => AnyEvent::Impl::Cocoa::],
+   [FLTK::                 => AnyEvent::Impl::FLTK2::],
 );
 
-our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);
+# all autoloaded methods reserve the complete glob, not just the method slot.
+# due to bugs in perls method cache implementation.
+our @methods = qw(io timer time now now_update signal child idle condvar);
 
 sub detect() {
-   unless ($MODEL) {
-      no strict 'refs';
+   local $!; # for good measure
+   local $SIG{__DIE__}; # we use eval
+
+   # free some memory
+   *detect = sub () { $MODEL };
+   # undef &func doesn't correctly update the method cache. grmbl.
+   # so we delete the whole glob. grmbl.
+   # otoh, perl doesn't let me undef an active usb, but it lets me free
+   # a glob with an active sub. hrm. i hope it works, but perl is
+   # usually buggy in this department. sigh.
+   delete @{"AnyEvent::"}{@methods};
+   undef @methods;
+
+   if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z0-9:]+)$/) {
+      my $model = $1;
+      $model = "AnyEvent::Impl::$model" unless $model =~ s/::$//;
+      if (eval "require $model") {
+         $MODEL = $model;
+         warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
+      } else {
+         warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
+      }
+   }
 
-      # check for already loaded models
+   # check for already loaded models
+   unless ($MODEL) {
       for (@REGISTRY, @models) {
          my ($package, $model) = @$_;
          if (${"$package\::VERSION"} > 0) {
             if (eval "require $model") {
                $MODEL = $model;
-               warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;
+               warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
                last;
             }
          }
       }
 
       unless ($MODEL) {
-         # try to load a model
-
+         # try to autoload a model
          for (@REGISTRY, @models) {
-            my ($package, $model) = @$_;
-            if (eval "require $package"
-                and ${"$package\::VERSION"} > 0
-                and eval "require $model") {
+            my ($package, $model, $autoload) = @$_;
+            if (
+               $autoload
+               and eval "require $package"
+               and ${"$package\::VERSION"} > 0
+               and eval "require $model"
+            ) {
                $MODEL = $model;
-               warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
+               warn "AnyEvent: autoloaded model '$model', using it.\n" if $VERBOSE >= 2;
                last;
             }
          }
 
          $MODEL
-           or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk.";
+           or die "AnyEvent: backend autodetection failed - did you properly install AnyEvent?\n";
       }
+   }
 
-      unshift @ISA, $MODEL;
-      push @{"$MODEL\::ISA"}, "AnyEvent::Base";
+   # free memory only needed for probing
+   undef @models;
+   undef @REGISTRY;
+
+   push @{"$MODEL\::ISA"}, "AnyEvent::Base";
+   unshift @ISA, $MODEL;
+
+   # now nuke some methods that are overridden by the backend.
+   # SUPER usage is not allowed in these.
+   for (qw(time signal child idle)) {
+      undef &{"AnyEvent::Base::$_"}
+         if defined &{"$MODEL\::$_"};
    }
 
+   if ($ENV{PERL_ANYEVENT_STRICT}) {
+      require AnyEvent::Strict;
+   }
+
+   if ($ENV{PERL_ANYEVENT_DEBUG_WRAP}) {
+      require AnyEvent::Debug;
+      AnyEvent::Debug::wrap ($ENV{PERL_ANYEVENT_DEBUG_WRAP});
+   }
+
+   if (exists $ENV{PERL_ANYEVENT_DEBUG_SHELL}) {
+      require AnyEvent::Socket;
+      require AnyEvent::Debug;
+
+      my ($host, $service) = AnyEvent::Socket::parse_hostport ($ENV{PERL_ANYEVENT_DEBUG_SHELL});
+      $AnyEvent::Debug::SHELL = AnyEvent::Debug::shell ($host, $service);
+   }
+
+   (shift @post_detect)->() while @post_detect;
+   undef @post_detect;
+
+   *post_detect = sub(&) {
+      shift->();
+
+      undef
+   };
+
    $MODEL
 }
 
-sub AUTOLOAD {
-   (my $func = $AUTOLOAD) =~ s/.*://;
+for my $name (@methods) {
+   *$name = sub {
+      detect;
+      # we use goto because
+      # a) it makes the thunk more transparent
+      # b) it allows us to delete the thunk later
+      goto &{ UNIVERSAL::can AnyEvent => "SUPER::$name" }
+   };
+}
 
-   $method{$func}
-      or croak "$func: not a valid method for AnyEvent objects";
+# utility function to dup a filehandle. this is used by many backends
+# to support binding more than one watcher per filehandle (they usually
+# allow only one watcher per fd, so we dup it to get a different one).
+sub _dupfh($$;$$) {
+   my ($poll, $fh, $r, $w) = @_;
 
-   detect unless $MODEL;
+   # cygwin requires the fh mode to be matching, unix doesn't
+   my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
 
-   my $class = shift;
-   $class->$func (@_);
+   open my $fh2, $mode, $fh
+      or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
+
+   # we assume CLOEXEC is already set by perl in all important cases
+
+   ($fh2, $rw)
+}
+
+=head1 SIMPLIFIED AE API
+
+Starting with version 5.0, AnyEvent officially supports a second, much
+simpler, API that is designed to reduce the calling, typing and memory
+overhead by using function call syntax and a fixed number of parameters.
+
+See the L<AE> manpage for details.
+
+=cut
+
+package AE;
+
+our $VERSION = $AnyEvent::VERSION;
+
+sub _reset() {
+   eval q{ 
+      # fall back to the main API by default - backends and AnyEvent::Base
+      # implementations can overwrite these.
+
+      sub io($$$) {
+         AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
+      }
+
+      sub timer($$$) {
+         AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
+      }
+
+      sub signal($$) {
+         AnyEvent->signal (signal => $_[0], cb => $_[1])
+      }
+
+      sub child($$) {
+         AnyEvent->child (pid => $_[0], cb => $_[1])
+      }
+
+      sub idle($) {
+         AnyEvent->idle (cb => $_[0]);
+      }
+
+      sub cv(;&) {
+         AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
+      }
+
+      sub now() {
+         AnyEvent->now
+      }
+
+      sub now_update() {
+         AnyEvent->now_update
+      }
+
+      sub time() {
+         AnyEvent->time
+      }
+
+      *postpone = \&AnyEvent::postpone;
+   };
+   die if $@;
 }
 
+BEGIN { _reset }
+
 package AnyEvent::Base;
 
-# default implementation for ->condvar, ->wait, ->broadcast
+# default implementations for many methods
 
-sub condvar {
-   bless \my $flag, "AnyEvent::Base::CondVar"
+sub time {
+   eval q{ # poor man's autoloading {}
+      # probe for availability of Time::HiRes
+      if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
+         warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
+         *AE::time = \&Time::HiRes::time;
+         # if (eval "use POSIX (); (POSIX::times())...
+      } else {
+         warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
+         *AE::time = sub (){ time }; # epic fail
+      }
+
+      *time = sub { AE::time }; # different prototypes
+   };
+   die if $@;
+
+   &time
 }
 
-sub AnyEvent::Base::CondVar::broadcast {
-   ${$_[0]}++;
+*now = \&time;
+
+sub now_update { }
+
+sub _poll {
+   Carp::croak "$AnyEvent::MODEL does not support blocking waits. Caught";
 }
 
-sub AnyEvent::Base::CondVar::wait {
-   AnyEvent->one_event while !${$_[0]};
+# default implementation for ->condvar
+# in fact, the default should not be overwritten
+
+sub condvar {
+   eval q{ # poor man's autoloading {}
+      *condvar = sub {
+         bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
+      };
+
+      *AE::cv = sub (;&) {
+         bless { @_ ? (_ae_cb => shift) : () }, "AnyEvent::CondVar"
+      };
+   };
+   die if $@;
+
+   &condvar
 }
 
 # default implementation for ->signal
 
-our %SIG_CB;
+our $HAVE_ASYNC_INTERRUPT;
 
-sub signal {
-   my (undef, %arg) = @_;
+sub _have_async_interrupt() {
+   $HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
+                              && eval "use Async::Interrupt 1.02 (); 1")
+      unless defined $HAVE_ASYNC_INTERRUPT;
 
-   my $signal = uc $arg{signal}
-      or Carp::croak "required option 'signal' is missing";
+   $HAVE_ASYNC_INTERRUPT
+}
 
-   $SIG_CB{$signal}{$arg{cb}} = $arg{cb};
-   $SIG{$signal} ||= sub {
-      $_->() for values %{ $SIG_CB{$signal} || {} };
-   };
+our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
+our (%SIG_ASY, %SIG_ASY_W);
+our ($SIG_COUNT, $SIG_TW);
+
+# install a dummy wakeup watcher to reduce signal catching latency
+# used by Impls
+sub _sig_add() {
+   unless ($SIG_COUNT++) {
+      # try to align timer on a full-second boundary, if possible
+      my $NOW = AE::now;
+
+      $SIG_TW = AE::timer
+         $MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
+         $MAX_SIGNAL_LATENCY,
+         sub { } # just for the PERL_ASYNC_CHECK
+      ;
+   }
+}
 
-   bless [$signal, $arg{cb}], "AnyEvent::Base::Signal"
+sub _sig_del {
+   undef $SIG_TW
+      unless --$SIG_COUNT;
 }
 
-sub AnyEvent::Base::Signal::DESTROY {
-   my ($signal, $cb) = @{$_[0]};
+our $_sig_name_init; $_sig_name_init = sub {
+   eval q{ # poor man's autoloading {}
+      undef $_sig_name_init;
+
+      if (_have_async_interrupt) {
+         *sig2num  = \&Async::Interrupt::sig2num;
+         *sig2name = \&Async::Interrupt::sig2name;
+      } else {
+         require Config;
+
+         my %signame2num;
+         @signame2num{ split ' ', $Config::Config{sig_name} }
+                        = split ' ', $Config::Config{sig_num};
+
+         my @signum2name;
+         @signum2name[values %signame2num] = keys %signame2num;
+
+         *sig2num = sub($) {
+            $_[0] > 0 ? shift : $signame2num{+shift}
+         };
+         *sig2name = sub ($) {
+            $_[0] > 0 ? $signum2name[+shift] : shift
+         };
+      }
+   };
+   die if $@;
+};
+
+sub sig2num ($) { &$_sig_name_init; &sig2num  }
+sub sig2name($) { &$_sig_name_init; &sig2name }
+
+sub signal {
+   eval q{ # poor man's autoloading {}
+      # probe for availability of Async::Interrupt 
+      if (_have_async_interrupt) {
+         warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
+
+         $SIGPIPE_R = new Async::Interrupt::EventPipe;
+         $SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
+
+      } else {
+         warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
+
+         if (AnyEvent::WIN32) {
+            require AnyEvent::Util;
+
+            ($SIGPIPE_R, $SIGPIPE_W) = AnyEvent::Util::portable_pipe ();
+            AnyEvent::Util::fh_nonblocking ($SIGPIPE_R, 1) if $SIGPIPE_R;
+            AnyEvent::Util::fh_nonblocking ($SIGPIPE_W, 1) if $SIGPIPE_W; # just in case
+         } else {
+            pipe $SIGPIPE_R, $SIGPIPE_W;
+            fcntl $SIGPIPE_R, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_R;
+            fcntl $SIGPIPE_W, AnyEvent::F_SETFL, AnyEvent::O_NONBLOCK if $SIGPIPE_W; # just in case
+
+            # not strictly required, as $^F is normally 2, but let's make sure...
+            fcntl $SIGPIPE_R, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
+            fcntl $SIGPIPE_W, AnyEvent::F_SETFD, AnyEvent::FD_CLOEXEC;
+         }
+
+         $SIGPIPE_R
+            or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
+
+         $SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
+      }
 
-   delete $SIG_CB{$signal}{$cb};
+      *signal = $HAVE_ASYNC_INTERRUPT
+         ? sub {
+              my (undef, %arg) = @_;
+
+              # async::interrupt
+              my $signal = sig2num $arg{signal};
+              $SIG_CB{$signal}{$arg{cb}} = $arg{cb};
+
+              $SIG_ASY{$signal} ||= new Async::Interrupt
+                 cb             => sub { undef $SIG_EV{$signal} },
+                 signal         => $signal,
+                 pipe           => [$SIGPIPE_R->filenos],
+                 pipe_autodrain => 0,
+              ;
+
+              bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
+           }
+         : sub {
+              my (undef, %arg) = @_;
+
+              # pure perl
+              my $signal = sig2name $arg{signal};
+              $SIG_CB{$signal}{$arg{cb}} = $arg{cb};
+
+              $SIG{$signal} ||= sub {
+                 local $!;
+                 syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
+                 undef $SIG_EV{$signal};
+              };
+
+              # can't do signal processing without introducing races in pure perl,
+              # so limit the signal latency.
+              _sig_add;
+
+              bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
+           }
+      ;
+
+      *AnyEvent::Base::signal::DESTROY = sub {
+         my ($signal, $cb) = @{$_[0]};
+
+         _sig_del;
+
+         delete $SIG_CB{$signal}{$cb};
+
+         $HAVE_ASYNC_INTERRUPT
+            ? delete $SIG_ASY{$signal}
+            : # delete doesn't work with older perls - they then
+              # print weird messages, or just unconditionally exit
+              # instead of getting the default action.
+              undef $SIG{$signal}
+            unless keys %{ $SIG_CB{$signal} };
+      };
+
+      *_signal_exec = sub {
+         $HAVE_ASYNC_INTERRUPT
+            ? $SIGPIPE_R->drain
+            : sysread $SIGPIPE_R, (my $dummy), 9;
+
+         while (%SIG_EV) {
+            for (keys %SIG_EV) {
+               delete $SIG_EV{$_};
+               &$_ for values %{ $SIG_CB{$_} || {} };
+            }
+         }
+      };
+   };
+   die if $@;
 
-   $SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
+   &signal
 }
 
 # default implementation for ->child
@@ -542,56 +1712,348 @@
 our %PID_CB;
 our $CHLD_W;
 our $CHLD_DELAY_W;
-our $PID_IDLE;
-our $WNOHANG;
 
-sub _child_wait {
-   while (0 < (my $pid = waitpid -1, $WNOHANG)) {
-      $_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
-                         (values %{ $PID_CB{0}    || {} });
-   }
+# used by many Impl's
+sub _emit_childstatus($$) {
+   my (undef, $rpid, $rstatus) = @_;
+
+   $_->($rpid, $rstatus)
+      for values %{ $PID_CB{$rpid} || {} },
+          values %{ $PID_CB{0}     || {} };
+}
+
+sub child {
+   eval q{ # poor man's autoloading {}
+      *_sigchld = sub {
+         my $pid;
+
+         AnyEvent->_emit_childstatus ($pid, $?)
+            while ($pid = waitpid -1, WNOHANG) > 0;
+      };
+
+      *child = sub {
+         my (undef, %arg) = @_;
+
+         my $pid = $arg{pid};
+         my $cb  = $arg{cb};
+
+         $PID_CB{$pid}{$cb+0} = $cb;
+
+         unless ($CHLD_W) {
+            $CHLD_W = AE::signal CHLD => \&_sigchld;
+            # child could be a zombie already, so make at least one round
+            &_sigchld;
+         }
 
-   undef $PID_IDLE;
+         bless [$pid, $cb+0], "AnyEvent::Base::child"
+      };
+
+      *AnyEvent::Base::child::DESTROY = sub {
+         my ($pid, $icb) = @{$_[0]};
+
+         delete $PID_CB{$pid}{$icb};
+         delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
+
+         undef $CHLD_W unless keys %PID_CB;
+      };
+   };
+   die if $@;
+
+   &child
 }
 
-sub _sigchld {
-   # make sure we deliver these changes "synchronous" with the event loop.
-   $CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub {
-      undef $CHLD_DELAY_W;
-      &_child_wait;
-   });
+# idle emulation is done by simply using a timer, regardless
+# of whether the process is idle or not, and not letting
+# the callback use more than 50% of the time.
+sub idle {
+   eval q{ # poor man's autoloading {}
+      *idle = sub {
+         my (undef, %arg) = @_;
+
+         my ($cb, $w, $rcb) = $arg{cb};
+
+         $rcb = sub {
+            if ($cb) {
+               $w = AE::time;
+               &$cb;
+               $w = AE::time - $w;
+
+               # never use more then 50% of the time for the idle watcher,
+               # within some limits
+               $w = 0.0001 if $w < 0.0001;
+               $w = 5      if $w > 5;
+
+               $w = AE::timer $w, 0, $rcb;
+            } else {
+               # clean up...
+               undef $w;
+               undef $rcb;
+            }
+         };
+
+         $w = AE::timer 0.05, 0, $rcb;
+
+         bless \\$cb, "AnyEvent::Base::idle"
+      };
+
+      *AnyEvent::Base::idle::DESTROY = sub {
+         undef $${$_[0]};
+      };
+   };
+   die if $@;
+
+   &idle
 }
 
-sub child {
-   my (undef, %arg) = @_;
+package AnyEvent::CondVar;
 
-   defined (my $pid = $arg{pid} + 0)
-      or Carp::croak "required option 'pid' is missing";
+our @ISA = AnyEvent::CondVar::Base::;
 
-   $PID_CB{$pid}{$arg{cb}} = $arg{cb};
+# only to be used for subclassing
+sub new {
+   my $class = shift;
+   bless AnyEvent->condvar (@_), $class
+}
 
-   unless ($WNOHANG) {
-      $WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
-   }
+package AnyEvent::CondVar::Base;
+
+#use overload
+#   '&{}'    => sub { my $self = shift; sub { $self->send (@_) } },
+#   fallback => 1;
+
+# save 300+ kilobytes by dirtily hardcoding overloading
+${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
+*{'AnyEvent::CondVar::Base::()'}   = sub { }; # "Make it findable via fetchmethod."
+*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
+${'AnyEvent::CondVar::Base::()'}   = 1; # fallback
+
+our $WAITING;
+
+sub _send {
+   # nop
+}
+
+sub _wait {
+   AnyEvent->_poll until $_[0]{_ae_sent};
+}
+
+sub send {
+   my $cv = shift;
+   $cv->{_ae_sent} = [@_];
+   (delete $cv->{_ae_cb})->($cv) if $cv->{_ae_cb};
+   $cv->_send;
+}
+
+sub croak {
+   $_[0]{_ae_croak} = $_[1];
+   $_[0]->send;
+}
+
+sub ready {
+   $_[0]{_ae_sent}
+}
 
-   unless ($CHLD_W) {
-      $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
-      # child could be a zombie already, so make at least one round
-      &_sigchld;
+sub recv {
+   unless ($_[0]{_ae_sent}) {
+      $WAITING
+         and Carp::croak "AnyEvent::CondVar: recursive blocking wait attempted";
+
+      local $WAITING = 1;
+      $_[0]->_wait;
    }
 
-   bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
+   $_[0]{_ae_croak}
+      and Carp::croak $_[0]{_ae_croak};
+
+   wantarray
+      ? @{ $_[0]{_ae_sent} }
+      : $_[0]{_ae_sent}[0]
 }
 
-sub AnyEvent::Base::Child::DESTROY {
-   my ($pid, $cb) = @{$_[0]};
+sub cb {
+   my $cv = shift;
+
+   @_
+      and $cv->{_ae_cb} = shift
+      and $cv->{_ae_sent}
+      and (delete $cv->{_ae_cb})->($cv);
+
+   $cv->{_ae_cb}
+}
 
-   delete $PID_CB{$pid}{$cb};
-   delete $PID_CB{$pid} unless keys %{ $PID_CB{$pid} };
+sub begin {
+   ++$_[0]{_ae_counter};
+   $_[0]{_ae_end_cb} = $_[1] if @_ > 1;
+}
 
-   undef $CHLD_W unless keys %PID_CB;
+sub end {
+   return if --$_[0]{_ae_counter};
+   &{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
 }
 
+# undocumented/compatibility with pre-3.4
+*broadcast = \&send;
+*wait      = \&recv;
+
+=head1 ERROR AND EXCEPTION HANDLING
+
+In general, AnyEvent does not do any error handling - it relies on the
+caller to do that if required. The L<AnyEvent::Strict> module (see also
+the C<PERL_ANYEVENT_STRICT> environment variable, below) provides strict
+checking of all AnyEvent methods, however, which is highly useful during
+development.
+
+As for exception handling (i.e. runtime errors and exceptions thrown while
+executing a callback), this is not only highly event-loop specific, but
+also not in any way wrapped by this module, as this is the job of the main
+program.
+
+The pure perl event loop simply re-throws the exception (usually
+within C<< condvar->recv >>), the L<Event> and L<EV> modules call C<<
+$Event/EV::DIED->() >>, L<Glib> uses C<< install_exception_handler >> and
+so on.
+
+=head1 ENVIRONMENT VARIABLES
+
+The following environment variables are used by this module or its
+submodules.
+
+Note that AnyEvent will remove I<all> environment variables starting with
+C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
+enabled.
+
+=over 4
+
+=item C<PERL_ANYEVENT_VERBOSE>
+
+By default, AnyEvent will be completely silent except in fatal
+conditions. You can set this environment variable to make AnyEvent more
+talkative.
+
+When set to C<1> or higher, causes AnyEvent to warn about unexpected
+conditions, such as not being able to load the event model specified by
+C<PERL_ANYEVENT_MODEL>.
+
+When set to C<2> or higher, cause AnyEvent to report to STDERR which event
+model it chooses.
+
+When set to C<8> or higher, then AnyEvent will report extra information on
+which optional modules it loads and how it implements certain features.
+
+=item C<PERL_ANYEVENT_STRICT>
+
+AnyEvent does not do much argument checking by default, as thorough
+argument checking is very costly. Setting this variable to a true value
+will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
+check the arguments passed to most method calls. If it finds any problems,
+it will croak.
+
+In other words, enables "strict" mode.
+
+Unlike C<use strict> (or its modern cousin, C<< use L<common::sense>
+>>, it is definitely recommended to keep it off in production. Keeping
+C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
+can be very useful, however.
+
+=item C<PERL_ANYEVENT_DEBUG_SHELL>
+
+If this env variable is set, then its contents will be
+interpreted by C<AnyEvent::Socket::parse_hostport> and an
+C<AnyEvent::Debug::shell> is bound on that port. The shell object is saved
+in C<$AnyEvent::Debug::SHELL>.
+
+For example, to bind a debug shell on a unix domain socket in
+F</tmp/debug.sock>, you could use this:
+
+   PERL_ANYEVENT_DEBUG_SHELL=unix/:/tmp/debug.sock perlprog
+
+=item C<PERL_ANYEVENT_DEBUG_WRAP>
+
+Can be set to C<0>, C<1> or C<2> and enables wrapping of all watchers for
+debugging purposes. See C<AnyEvent::Debug::wrap> for details.
+
+=item C<PERL_ANYEVENT_MODEL>
+
+This can be used to specify the event model to be used by AnyEvent, before
+auto detection and -probing kicks in.
+
+It normally is a string consisting entirely of ASCII letters (e.g. C<EV>
+or C<IOAsync>). The string C<AnyEvent::Impl::> gets prepended and the
+resulting module name is loaded and - if the load was successful - used as
+event model backend. If it fails to load then AnyEvent will proceed with
+auto detection and -probing.
+
+If the string ends with C<::> instead (e.g. C<AnyEvent::Impl::EV::>) then
+nothing gets prepended and the module name is used as-is (hint: C<::> at
+the end of a string designates a module name and quotes it appropriately).
+
+For example, to force the pure perl model (L<AnyEvent::Loop::Perl>) you
+could start your program like this:
+
+   PERL_ANYEVENT_MODEL=Perl perl ...
+
+=item C<PERL_ANYEVENT_PROTOCOLS>
+
+Used by both L<AnyEvent::DNS> and L<AnyEvent::Socket> to determine preferences
+for IPv4 or IPv6. The default is unspecified (and might change, or be the result
+of auto probing).
+
+Must be set to a comma-separated list of protocols or address families,
+current supported: C<ipv4> and C<ipv6>. Only protocols mentioned will be
+used, and preference will be given to protocols mentioned earlier in the
+list.
+
+This variable can effectively be used for denial-of-service attacks
+against local programs (e.g. when setuid), although the impact is likely
+small, as the program has to handle conenction and other failures anyways.
+
+Examples: C<PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6> - prefer IPv4 over IPv6,
+but support both and try to use both.  C<PERL_ANYEVENT_PROTOCOLS=ipv4>
+- only support IPv4, never try to resolve or contact IPv6
+addresses. C<PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4> support either IPv4 or
+IPv6, but prefer IPv6 over IPv4.
+
+=item C<PERL_ANYEVENT_EDNS0>
+
+Used by L<AnyEvent::DNS> to decide whether to use the EDNS0 extension
+for DNS. This extension is generally useful to reduce DNS traffic, but
+some (broken) firewalls drop such DNS packets, which is why it is off by
+default.
+
+Setting this variable to C<1> will cause L<AnyEvent::DNS> to announce
+EDNS0 in its DNS requests.
+
+=item C<PERL_ANYEVENT_MAX_FORKS>
+
+The maximum number of child processes that C<AnyEvent::Util::fork_call>
+will create in parallel.
+
+=item C<PERL_ANYEVENT_MAX_OUTSTANDING_DNS>
+
+The default value for the C<max_outstanding> parameter for the default DNS
+resolver - this is the maximum number of parallel DNS requests that are
+sent to the DNS server.
+
+=item C<PERL_ANYEVENT_RESOLV_CONF>
+
+The file to use instead of F</etc/resolv.conf> (or OS-specific
+configuration) in the default resolver. When set to the empty string, no
+default config will be used.
+
+=item C<PERL_ANYEVENT_CA_FILE>, C<PERL_ANYEVENT_CA_PATH>.
+
+When neither C<ca_file> nor C<ca_path> was specified during
+L<AnyEvent::TLS> context creation, and either of these environment
+variables exist, they will be used to specify CA certificate locations
+instead of a system-dependent default.
+
+=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
+
+When these are set to C<1>, then the respective modules are not
+loaded. Mostly good for testing AnyEvent itself.
+
+=back
+
 =head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
 
 This is an advanced topic that you do not normally need to use AnyEvent in
@@ -635,16 +2097,9 @@
 C<die>. This still works with most modules/usages, and blocking calls must
 not be done in an interactive application, so it makes sense.
 
-=head1 ENVIRONMENT VARIABLES
-
-The following environment variables are used by this module:
-
-C<PERL_ANYEVENT_VERBOSE> when set to C<2> or higher, cause AnyEvent to
-report to STDERR which event model it chooses.
-
 =head1 EXAMPLE PROGRAM
 
-The following program uses an IO watcher to read data from STDIN, a timer
+The following program uses an I/O watcher to read data from STDIN, a timer
 to display a message once per second, and a condition variable to quit the
 program when the user enters quit:
 
@@ -659,22 +2114,15 @@
          warn "io event <$_[0]>\n";   # will always output <r>
          chomp (my $input = <STDIN>); # read a line
          warn "read: $input\n";       # output what has been read
-         $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
+         $cv->send if $input =~ /^q/i; # quit program if /^q/i
       },
    );
 
-   my $time_watcher; # can only be used once
-
-   sub new_timer {
-      $timer = AnyEvent->timer (after => 1, cb => sub {
-         warn "timeout\n"; # print 'timeout' about every second
-         &new_timer; # and restart the time
-      });
-   }
-
-   new_timer; # create first timer
+   my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
+      warn "timeout\n"; # print 'timeout' at most every second
+   });
 
-   $cv->wait; # wait until user enters /^q/i
+   $cv->recv; # wait until user enters /^q/i
 
 =head1 REAL-WORLD EXAMPLE
 
@@ -734,13 +2182,13 @@
    $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r });
 
 Again, C<fh_ready_r> waits till all data has arrived, and then stores the
-result and signals any possible waiters that the request ahs finished:
+result and signals any possible waiters that the request has finished:
 
    sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf};
 
    if (end-of-file or data complete) {
      $txn->{result} = $txn->{buf};
-     $txn->{finished}->broadcast;
+     $txn->{finished}->send;
      $txb->{cb}->($txn) of $txn->{cb}; # also call callback
    }
 
@@ -748,14 +2196,14 @@
 request was already finished, it doesn't wait, of course, and returns the
 data:
 
-   $txn->{finished}->wait;
+   $txn->{finished}->recv;
    return $txn->{result};
 
 The actual code goes further and collects all errors (C<die>s, exceptions)
-that occured during request processing. The C<result> method detects
+that occurred during request processing. The C<result> method detects
 whether an exception as thrown (it is stored inside the $txn object)
 and just throws the exception, which means connection errors and other
-problems get reported tot he code that tries to use the result, not in a
+problems get reported to the code that tries to use the result, not in a
 random callback.
 
 All of this enables the following usage styles:
@@ -793,26 +2241,562 @@
 
    $fcp->txn_client_get ($url)->cb (sub {
       ...
-      $quit->broadcast;
+      $quit->send;
    });
 
-   $quit->wait;
+   $quit->recv;
+
+
+=head1 BENCHMARKS
+
+To give you an idea of the performance and overheads that AnyEvent adds
+over the event loops themselves and to give you an impression of the speed
+of various event loops I prepared some benchmarks.
+
+=head2 BENCHMARKING ANYEVENT OVERHEAD
+
+Here is a benchmark of various supported event models used natively and
+through AnyEvent. The benchmark creates a lot of timers (with a zero
+timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
+which it is), lets them fire exactly once and destroys them again.
+
+Source code for this benchmark is found as F<eg/bench> in the AnyEvent
+distribution. It uses the L<AE> interface, which makes a real difference
+for the EV and Perl backends only.
+
+=head3 Explanation of the columns
+
+I<watcher> is the number of event watchers created/destroyed. Since
+different event models feature vastly different performances, each event
+loop was given a number of watchers so that overall runtime is acceptable
+and similar between tested event loop (and keep them from crashing): Glib
+would probably take thousands of years if asked to process the same number
+of watchers as EV in this benchmark.
+
+I<bytes> is the number of bytes (as measured by the resident set size,
+RSS) consumed by each watcher. This method of measuring captures both C
+and Perl-based overheads.
+
+I<create> is the time, in microseconds (millionths of seconds), that it
+takes to create a single watcher. The callback is a closure shared between
+all watchers, to avoid adding memory overhead. That means closure creation
+and memory usage is not included in the figures.
+
+I<invoke> is the time, in microseconds, used to invoke a simple
+callback. The callback simply counts down a Perl variable and after it was
+invoked "watcher" times, it would C<< ->send >> a condvar once to
+signal the end of this phase.
+
+I<destroy> is the time, in microseconds, that it takes to destroy a single
+watcher.
+
+=head3 Results
+
+          name watchers bytes create invoke destroy comment
+         EV/EV   100000   223   0.47   0.43    0.27 EV native interface
+        EV/Any   100000   223   0.48   0.42    0.26 EV + AnyEvent watchers
+  Coro::EV/Any   100000   223   0.47   0.42    0.26 coroutines + Coro::Signal
+      Perl/Any   100000   431   2.70   0.74    0.92 pure perl implementation
+   Event/Event    16000   516  31.16  31.84    0.82 Event native interface
+     Event/Any    16000  1203  42.61  34.79    1.80 Event + AnyEvent watchers
+   IOAsync/Any    16000  1911  41.92  27.45   16.81 via IO::Async::Loop::IO_Poll
+   IOAsync/Any    16000  1726  40.69  26.37   15.25 via IO::Async::Loop::Epoll
+      Glib/Any    16000  1118  89.00  12.57   51.17 quadratic behaviour
+        Tk/Any     2000  1346  20.96  10.75    8.00 SEGV with >> 2000 watchers
+       POE/Any     2000  6951 108.97 795.32   14.24 via POE::Loop::Event
+       POE/Any     2000  6648  94.79 774.40  575.51 via POE::Loop::Select
+
+=head3 Discussion
+
+The benchmark does I<not> measure scalability of the event loop very
+well. For example, a select-based event loop (such as the pure perl one)
+can never compete with an event loop that uses epoll when the number of
+file descriptors grows high. In this benchmark, all events become ready at
+the same time, so select/poll-based implementations get an unnatural speed
+boost.
+
+Also, note that the number of watchers usually has a nonlinear effect on
+overall speed, that is, creating twice as many watchers doesn't take twice
+the time - usually it takes longer. This puts event loops tested with a
+higher number of watchers at a disadvantage.
+
+To put the range of results into perspective, consider that on the
+benchmark machine, handling an event takes roughly 1600 CPU cycles with
+EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU
+cycles with POE.
+
+C<EV> is the sole leader regarding speed and memory use, which are both
+maximal/minimal, respectively. When using the L<AE> API there is zero
+overhead (when going through the AnyEvent API create is about 5-6 times
+slower, with other times being equal, so still uses far less memory than
+any other event loop and is still faster than Event natively).
+
+The pure perl implementation is hit in a few sweet spots (both the
+constant timeout and the use of a single fd hit optimisations in the perl
+interpreter and the backend itself). Nevertheless this shows that it
+adds very little overhead in itself. Like any select-based backend its
+performance becomes really bad with lots of file descriptors (and few of
+them active), of course, but this was not subject of this benchmark.
+
+The C<Event> module has a relatively high setup and callback invocation
+cost, but overall scores in on the third place.
+
+C<IO::Async> performs admirably well, about on par with C<Event>, even
+when using its pure perl backend.
+
+C<Glib>'s memory usage is quite a bit higher, but it features a
+faster callback invocation and overall ends up in the same class as
+C<Event>. However, Glib scales extremely badly, doubling the number of
+watchers increases the processing time by more than a factor of four,
+making it completely unusable when using larger numbers of watchers
+(note that only a single file descriptor was used in the benchmark, so
+inefficiencies of C<poll> do not account for this).
+
+The C<Tk> adaptor works relatively well. The fact that it crashes with
+more than 2000 watchers is a big setback, however, as correctness takes
+precedence over speed. Nevertheless, its performance is surprising, as the
+file descriptor is dup()ed for each watcher. This shows that the dup()
+employed by some adaptors is not a big performance issue (it does incur a
+hidden memory cost inside the kernel which is not reflected in the figures
+above).
+
+C<POE>, regardless of underlying event loop (whether using its pure perl
+select-based backend or the Event module, the POE-EV backend couldn't
+be tested because it wasn't working) shows abysmal performance and
+memory usage with AnyEvent: Watchers use almost 30 times as much memory
+as EV watchers, and 10 times as much memory as Event (the high memory
+requirements are caused by requiring a session for each watcher). Watcher
+invocation speed is almost 900 times slower than with AnyEvent's pure perl
+implementation.
+
+The design of the POE adaptor class in AnyEvent can not really account
+for the performance issues, though, as session creation overhead is
+small compared to execution of the state machine, which is coded pretty
+optimally within L<AnyEvent::Impl::POE> (and while everybody agrees that
+using multiple sessions is not a good approach, especially regarding
+memory usage, even the author of POE could not come up with a faster
+design).
+
+=head3 Summary
+
+=over 4
+
+=item * Using EV through AnyEvent is faster than any other event loop
+(even when used without AnyEvent), but most event loops have acceptable
+performance with or without AnyEvent.
+
+=item * The overhead AnyEvent adds is usually much smaller than the overhead of
+the actual event loop, only with extremely fast event loops such as EV
+adds AnyEvent significant overhead.
+
+=item * You should avoid POE like the plague if you want performance or
+reasonable memory usage.
+
+=back
+
+=head2 BENCHMARKING THE LARGE SERVER CASE
+
+This benchmark actually benchmarks the event loop itself. It works by
+creating a number of "servers": each server consists of a socket pair, a
+timeout watcher that gets reset on activity (but never fires), and an I/O
+watcher waiting for input on one side of the socket. Each time the socket
+watcher reads a byte it will write that byte to a random other "server".
+
+The effect is that there will be a lot of I/O watchers, only part of which
+are active at any one point (so there is a constant number of active
+fds for each loop iteration, but which fds these are is random). The
+timeout is reset each time something is read because that reflects how
+most timeouts work (and puts extra pressure on the event loops).
+
+In this benchmark, we use 10000 socket pairs (20000 sockets), of which 100
+(1%) are active. This mirrors the activity of large servers with many
+connections, most of which are idle at any one point in time.
+
+Source code for this benchmark is found as F<eg/bench2> in the AnyEvent
+distribution. It uses the L<AE> interface, which makes a real difference
+for the EV and Perl backends only.
+
+=head3 Explanation of the columns
+
+I<sockets> is the number of sockets, and twice the number of "servers" (as
+each server has a read and write socket end).
+
+I<create> is the time it takes to create a socket pair (which is
+nontrivial) and two watchers: an I/O watcher and a timeout watcher.
+
+I<request>, the most important value, is the time it takes to handle a
+single "request", that is, reading the token from the pipe and forwarding
+it to another server. This includes deleting the old timeout and creating
+a new one that moves the timeout into the future.
+
+=head3 Results
+
+     name sockets create  request 
+       EV   20000  62.66     7.99 
+     Perl   20000  68.32    32.64 
+  IOAsync   20000 174.06   101.15 epoll
+  IOAsync   20000 174.67   610.84 poll
+    Event   20000 202.69   242.91 
+     Glib   20000 557.01  1689.52 
+      POE   20000 341.54 12086.32 uses POE::Loop::Event
+
+=head3 Discussion
+
+This benchmark I<does> measure scalability and overall performance of the
+particular event loop.
+
+EV is again fastest. Since it is using epoll on my system, the setup time
+is relatively high, though.
+
+Perl surprisingly comes second. It is much faster than the C-based event
+loops Event and Glib.
+
+IO::Async performs very well when using its epoll backend, and still quite
+good compared to Glib when using its pure perl backend.
+
+Event suffers from high setup time as well (look at its code and you will
+understand why). Callback invocation also has a high overhead compared to
+the C<< $_->() for .. >>-style loop that the Perl event loop uses. Event
+uses select or poll in basically all documented configurations.
+
+Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It
+clearly fails to perform with many filehandles or in busy servers.
+
+POE is still completely out of the picture, taking over 1000 times as long
+as EV, and over 100 times as long as the Perl implementation, even though
+it uses a C-based event loop in this case.
+
+=head3 Summary
+
+=over 4
+
+=item * The pure perl implementation performs extremely well.
+
+=item * Avoid Glib or POE in large projects where performance matters.
+
+=back
+
+=head2 BENCHMARKING SMALL SERVERS
+
+While event loops should scale (and select-based ones do not...) even to
+large servers, most programs we (or I :) actually write have only a few
+I/O watchers.
+
+In this benchmark, I use the same benchmark program as in the large server
+case, but it uses only eight "servers", of which three are active at any
+one time. This should reflect performance for a small server relatively
+well.
+
+The columns are identical to the previous table.
+
+=head3 Results
+
+    name sockets create request 
+      EV      16  20.00    6.54 
+    Perl      16  25.75   12.62 
+   Event      16  81.27   35.86 
+    Glib      16  32.63   15.48 
+     POE      16 261.87  276.28 uses POE::Loop::Event
+
+=head3 Discussion
+
+The benchmark tries to test the performance of a typical small
+server. While knowing how various event loops perform is interesting, keep
+in mind that their overhead in this case is usually not as important, due
+to the small absolute number of watchers (that is, you need efficiency and
+speed most when you have lots of watchers, not when you only have a few of
+them).
+
+EV is again fastest.
+
+Perl again comes second. It is noticeably faster than the C-based event
+loops Event and Glib, although the difference is too small to really
+matter.
+
+POE also performs much better in this case, but is is still far behind the
+others.
+
+=head3 Summary
+
+=over 4
+
+=item * C-based event loops perform very well with small number of
+watchers, as the management overhead dominates.
+
+=back
+
+=head2 THE IO::Lambda BENCHMARK
+
+Recently I was told about the benchmark in the IO::Lambda manpage, which
+could be misinterpreted to make AnyEvent look bad. In fact, the benchmark
+simply compares IO::Lambda with POE, and IO::Lambda looks better (which
+shouldn't come as a surprise to anybody). As such, the benchmark is
+fine, and mostly shows that the AnyEvent backend from IO::Lambda isn't
+very optimal. But how would AnyEvent compare when used without the extra
+baggage? To explore this, I wrote the equivalent benchmark for AnyEvent.
+
+The benchmark itself creates an echo-server, and then, for 500 times,
+connects to the echo server, sends a line, waits for the reply, and then
+creates the next connection. This is a rather bad benchmark, as it doesn't
+test the efficiency of the framework or much non-blocking I/O, but it is a
+benchmark nevertheless.
+
+   name                    runtime
+   Lambda/select           0.330 sec
+      + optimized          0.122 sec
+   Lambda/AnyEvent         0.327 sec
+      + optimized          0.138 sec
+   Raw sockets/select      0.077 sec
+   POE/select, components  0.662 sec
+   POE/select, raw sockets 0.226 sec
+   POE/select, optimized   0.404 sec
+
+   AnyEvent/select/nb      0.085 sec
+   AnyEvent/EV/nb          0.068 sec
+      +state machine       0.134 sec
+
+The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
+benchmarks actually make blocking connects and use 100% blocking I/O,
+defeating the purpose of an event-based solution. All of the newly
+written AnyEvent benchmarks use 100% non-blocking connects (using
+AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
+resolver), so AnyEvent is at a disadvantage here, as non-blocking connects
+generally require a lot more bookkeeping and event handling than blocking
+connects (which involve a single syscall only).
+
+The last AnyEvent benchmark additionally uses L<AnyEvent::Handle>, which
+offers similar expressive power as POE and IO::Lambda, using conventional
+Perl syntax. This means that both the echo server and the client are 100%
+non-blocking, further placing it at a disadvantage.
+
+As you can see, the AnyEvent + EV combination even beats the
+hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
+backend easily beats IO::Lambda and POE.
+
+And even the 100% non-blocking version written using the high-level (and
+slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
+higher level ("unoptimised") abstractions by a large margin, even though
+it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
+
+The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
+F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
+part of the IO::Lambda distribution and were used without any changes.
+
+
+=head1 SIGNALS
+
+AnyEvent currently installs handlers for these signals:
+
+=over 4
+
+=item SIGCHLD
+
+A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
+emulation for event loops that do not support them natively. Also, some
+event loops install a similar handler.
+
+Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
+AnyEvent will reset it to default, to avoid losing child exit statuses.
+
+=item SIGPIPE
+
+A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
+when AnyEvent gets loaded.
+
+The rationale for this is that AnyEvent users usually do not really depend
+on SIGPIPE delivery (which is purely an optimisation for shell use, or
+badly-written programs), but C<SIGPIPE> can cause spurious and rare
+program exits as a lot of people do not expect C<SIGPIPE> when writing to
+some random socket.
+
+The rationale for installing a no-op handler as opposed to ignoring it is
+that this way, the handler will be restored to defaults on exec.
+
+Feel free to install your own handler, or reset it to defaults.
+
+=back
+
+=cut
+
+undef $SIG{CHLD}
+   if $SIG{CHLD} eq 'IGNORE';
+
+$SIG{PIPE} = sub { }
+   unless defined $SIG{PIPE};
+
+=head1 RECOMMENDED/OPTIONAL MODULES
+
+One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
+its built-in modules) are required to use it.
+
+That does not mean that AnyEvent won't take advantage of some additional
+modules if they are installed.
+
+This section explains which additional modules will be used, and how they
+affect AnyEvent's operation.
+
+=over 4
+
+=item L<Async::Interrupt>
+
+This slightly arcane module is used to implement fast signal handling: To
+my knowledge, there is no way to do completely race-free and quick
+signal handling in pure perl. To ensure that signals still get
+delivered, AnyEvent will start an interval timer to wake up perl (and
+catch the signals) with some delay (default is 10 seconds, look for
+C<$AnyEvent::MAX_SIGNAL_LATENCY>).
+
+If this module is available, then it will be used to implement signal
+catching, which means that signals will not be delayed, and the event loop
+will not be interrupted regularly, which is more efficient (and good for
+battery life on laptops).
+
+This affects not just the pure-perl event loop, but also other event loops
+that have no signal handling on their own (e.g. Glib, Tk, Qt).
+
+Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
+and either employ their own workarounds (POE) or use AnyEvent's workaround
+(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
+does nothing for those backends.
+
+=item L<EV>
+
+This module isn't really "optional", as it is simply one of the backend
+event loops that AnyEvent can use. However, it is simply the best event
+loop available in terms of features, speed and stability: It supports
+the AnyEvent API optimally, implements all the watcher types in XS, does
+automatic timer adjustments even when no monotonic clock is available,
+can take avdantage of advanced kernel interfaces such as C<epoll> and
+C<kqueue>, and is the fastest backend I<by far>. You can even embed
+L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
+
+If you only use backends that rely on another event loop (e.g. C<Tk>),
+then this module will do nothing for you.
+
+=item L<Guard>
+
+The guard module, when used, will be used to implement
+C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
+lot less memory), but otherwise doesn't affect guard operation much. It is
+purely used for performance.
+
+=item L<JSON> and L<JSON::XS>
+
+One of these modules is required when you want to read or write JSON data
+via L<AnyEvent::Handle>. L<JSON> is also written in pure-perl, but can take
+advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
+
+=item L<Net::SSLeay>
+
+Implementing TLS/SSL in Perl is certainly interesting, but not very
+worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
+the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
+
+=item L<Time::HiRes>
+
+This module is part of perl since release 5.008. It will be used when the
+chosen event library does not come with a timing source of its own. The
+pure-perl event loop (L<AnyEvent::Loop>) will additionally load it to
+try to use a monotonic clock for timing stability.
+
+=back
+
+
+=head1 FORK
+
+Most event libraries are not fork-safe. The ones who are usually are
+because they rely on inefficient but fork-safe C<select> or C<poll> calls
+- higher performance APIs such as BSD's kqueue or the dreaded Linux epoll
+are usually badly thought-out hacks that are incompatible with fork in
+one way or another. Only L<EV> is fully fork-aware and ensures that you
+continue event-processing in both parent and child (or both, if you know
+what you are doing).
+
+This means that, in general, you cannot fork and do event processing in
+the child if the event library was initialised before the fork (which
+usually happens when the first AnyEvent watcher is created, or the library
+is loaded).
+
+If you have to fork, you must either do so I<before> creating your first
+watcher OR you must not use AnyEvent at all in the child OR you must do
+something completely out of the scope of AnyEvent.
+
+The problem of doing event processing in the parent I<and> the child
+is much more complicated: even for backends that I<are> fork-aware or
+fork-safe, their behaviour is not usually what you want: fork clones all
+watchers, that means all timers, I/O watchers etc. are active in both
+parent and child, which is almost never what you want. USing C<exec>
+to start worker children from some kind of manage rprocess is usually
+preferred, because it is much easier and cleaner, at the expense of having
+to have another binary.
+
+
+=head1 SECURITY CONSIDERATIONS
+
+AnyEvent can be forced to load any event model via
+$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to
+execute arbitrary code or directly gain access, it can easily be used to
+make the program hang or malfunction in subtle ways, as AnyEvent watchers
+will not be active when the program uses a different event model than
+specified in the variable.
+
+You can make AnyEvent completely ignore this variable by deleting it
+before the first watcher gets created, e.g. with a C<BEGIN> block:
+
+   BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
+  
+   use AnyEvent;
+
+Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
+be used to probe what backend is used and gain other information (which is
+probably even less useful to an attacker than PERL_ANYEVENT_MODEL), and
+$ENV{PERL_ANYEVENT_STRICT}.
+
+Note that AnyEvent will remove I<all> environment variables starting with
+C<PERL_ANYEVENT_> from C<%ENV> when it is loaded while taint mode is
+enabled.
+
+
+=head1 BUGS
+
+Perl 5.8 has numerous memleaks that sometimes hit this module and are hard
+to work around. If you suffer from memleaks, first upgrade to Perl 5.10
+and check wether the leaks still show up. (Perl 5.10.0 has other annoying
+memleaks, such as leaking on C<map> and C<grep> but it is usually not as
+pronounced).
+
 
 =head1 SEE ALSO
 
-Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
-L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>.
+Tutorial/Introduction: L<AnyEvent::Intro>.
+
+FAQ: L<AnyEvent::FAQ>.
+
+Utility functions: L<AnyEvent::Util>.
+
+Event modules: L<AnyEvent::Loop>, L<EV>, L<EV::Glib>, L<Glib::EV>,
+L<Event>, L<Glib::Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>, L<POE>.
+
+Implementations: L<AnyEvent::Impl::EV>, L<AnyEvent::Impl::Event>,
+L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>,
+L<AnyEvent::Impl::EventLib>, L<AnyEvent::Impl::Qt>,
+L<AnyEvent::Impl::POE>, L<AnyEvent::Impl::IOAsync>, L<Anyevent::Impl::Irssi>.
+
+Non-blocking file handles, sockets, TCP clients and
+servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>, L<AnyEvent::TLS>.
+
+Asynchronous DNS: L<AnyEvent::DNS>.
+
+Thread support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>.
 
-Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
-L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>,
-L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>.
+Nontrivial usage examples: L<AnyEvent::GPSD>, L<AnyEvent::IRC>,
+L<AnyEvent::HTTP>.
 
-Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
 
 =head1 AUTHOR
 
- Marc Lehmann <schmorp@schmorp.de>
- http://home.schmorp.de/
+   Marc Lehmann <schmorp@schmorp.de>
+   http://home.schmorp.de/
 
 =cut