--- AnyEvent/lib/AnyEvent.pm	2006/12/31 11:54:43	1.22
+++ AnyEvent/lib/AnyEvent.pm	2008/07/08 23:53:37	1.168
@@ -2,7 +2,7 @@
 
 AnyEvent - provide framework for multiple event loops
 
-Event, Coro, Glib, Tk, Perl - various supported event loops
+EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
 
 =head1 SYNOPSIS
 
@@ -16,9 +16,70 @@
       ...
    });
 
-   my $w = AnyEvent->condvar; # stores wether a condition was flagged
-   $w->wait; # enters "main loop" till $condvar gets ->broadcast
-   $w->broadcast; # wake up current and all future wait's
+   my $w = AnyEvent->condvar; # stores whether a condition was flagged
+   $w->send; # wake up current and all future recv's
+   $w->recv; # enters "main loop" till $condvar gets ->send
+
+=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 WHY YOU SHOULD USE THIS MODULE (OR NOT)
+
+Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
+nowadays. So what is different about AnyEvent?
+
+Executive Summary: AnyEvent is I<compatible>, AnyEvent is I<free of
+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
+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
+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
+religion, a way of living, and most importantly: without forcing your
+module users into the same thing by forcing them to use the same event
+model you use.
+
+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 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 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).
+
+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 enormous amount of code and strict rules you have to
+follow. AnyEvent, on the other hand, is lean and up to the point, by only
+offering the functionality that is necessary, in as thin as a wrapper as
+technically possible.
+
+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
 
@@ -27,19 +88,22 @@
 users to use the same event loop (as only a single event loop can coexist
 peacefully at any one time).
 
-The interface itself is vaguely similar but not identical to the Event
+The interface itself is vaguely similar, but not identical to the L<Event>
 module.
 
-On the first call of any method, the module tries to detect the currently
-loaded event loop by probing wether any of the following modules is
-loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is
-used. If none is found, the module tries to load these modules in the
-order given. The first one that could be successfully loaded will be
-used. If still none could be found, AnyEvent will fall back to a pure-perl
-event loop, which is also not very efficient.
+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<EV>,
+L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
+L<POE>. The first one found is used. If none are found, the module tries
+to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl
+adaptor should always succeed) in the order given. 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.
 
 Because AnyEvent first checks for modules that are already loaded, loading
-an Event model explicitly before first using AnyEvent will likely make
+an event model explicitly before first using AnyEvent will likely make
 that model the default. For example:
 
    use Tk;
@@ -47,44 +111,71 @@
 
    # .. 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.
+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. To disable the watcher you have to destroy it (e.g. by
-setting the variable that stores it to C<undef> or otherwise deleting all
-references to it).
+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
+variable you store it in to C<undef> or otherwise deleting all references
+to it).
 
 All watchers are created by calling a method on the C<AnyEvent> class.
 
-=head2 IO WATCHERS
+Many watchers either are used with "recursion" (repeating timers for
+example), or need to refer to their watcher object in other ways.
 
-You can create I/O watcher by calling the C<< AnyEvent->io >> method with
-the following mandatory arguments:
+An any way to achieve that is this pattern:
 
-C<fh> the Perl I<filehandle> (not filedescriptor) to watch for
-events. C<poll> must be a string that is either C<r> or C<w>, that creates
-a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback
-to invoke everytime the filehandle becomes ready.
-
-Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on
-a socket you can have one r + one w, not any more (limitation comes from
-Tk - if you are sure you are not using Tk this limitation is gone).
+   my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
+      # you can use $w here, for example to undef it
+      undef $w;
+   });
 
-Filehandles will be kept alive, so as long as the watcher exists, the
-filehandle exists, too.
+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 I/O WATCHERS
+
+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
+(AnyEvent might or might not keep a reference to this file handle). 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.
+
+Some event loops issue spurious readyness 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";
@@ -96,94 +187,424 @@
 You can create a time watcher by calling the C<< AnyEvent->timer >>
 method with the following mandatory arguments:
 
-C<after> after how many seconds (fractions are supported) should the timer
-activate. C<cb> the callback to invoke.
+C<after> specifies after how many seconds (fractional values are
+supported) the callback should be invoked. C<cb> is the callback to invoke
+in that case.
+
+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 once only. 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 missing.
+
+The callback will be rescheduled before invoking the callback, but no
+attempt is done to avoid timer drift in most backends, so the interval is
+only approximate.
 
-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).
+Example: fire an event after 7.7 seconds.
 
-Example:
-
-   # fire an event after 7.7 seconds
    my $w = AnyEvent->timer (after => 7.7, cb => sub {
       warn "timeout\n";
    });
 
    # to cancel the timer:
-   undef $w
+   undef $w;
+
+Example 2: fire an event after 0.5 seconds, then roughly every second.
+
+   my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
+      warn "timeout\n";
+   };
 
-=head2 CONDITION WATCHERS
+=head3 TIMING ISSUES
 
-Condition watchers can be created by calling the C<< AnyEvent->condvar >>
-method without any arguments.
+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 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, based
+on true relative time) and absolute (ev_periodic, based on wallclock time)
+timers.
 
-A condition watcher watches for a condition - precisely that the C<<
-->broadcast >> method has been called.
+AnyEvent always prefers relative timers, if available, matching the
+AnyEvent API.
 
-The watcher has only two methods:
+AnyEvent has two additional methods that return the "current time":
 
 =over 4
 
-=item $cv->wait
+=item AnyEvent->time
 
-Wait (blocking if necessary) until the C<< ->broadcast >> method has been
-called on c<$cv>, while servicing other watchers normally.
+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 it's 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 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 callback 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.
 
-Not all event models support a blocking wait - some die in that case, so
-if you are using this from a module, never require a blocking wait, but
-let the caller decide wether 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 blockign waits if the caller so desires).
-
-You can only wait once on a condition - additional calls will return
-immediately.
-
-=item $cv->broadcast
-
-Flag the condition as ready - a running C<< ->wait >> and all further
-calls to C<wait> will return after this method has been called. If nobody
-is waiting the broadcast will be remembered..
+=back
 
-Example:
+=head2 SIGNAL WATCHERS
+
+You can watch for signals using a signal watcher, C<signal> is the signal
+I<name> in uppercase and without any C<SIG> prefix, C<cb> is the Perl
+callback to be invoked whenever a signal occurs.
+
+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 guaranteed not to interrupt any other callbacks.
+
+The main advantage of using these watchers is that you can share a signal
+between multiple watchers.
+
+This watcher might use C<%SIG>, 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 });
+
+=head2 CHILD PROCESS WATCHERS
+
+You can also watch on a child process exit and catch its exit status.
+
+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), so unlike other watcher types,
+you I<can> rely on child watcher callback arguments.
+
+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 (POE doesn't), 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).
+
+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>).
+
+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 CONDITION VARIABLES
+
+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 different, it expects somebody else to run the event loop and
+will only block when necessary (usually when told by the user).
+
+The instrument to do that is called a "condition variable", so called
+because they represent a condition that must become true.
+
+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.
+
+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).
+
+Condition variables are similar to callbacks, except that you can
+optionally wait for them. They can also be called merge points - points
+in time where multiple outstanding events have been processed. And yet
+another way to call them is transactions - each condition variable can be
+used to represent a transaction, which finishes at some point and delivers
+a result.
+
+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. The user can either act when the callback is
+called or can synchronously C<< ->recv >> for the results.
+
+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 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.
+
+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
+it's 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.
 
    # wait till the result is ready
    my $result_ready = AnyEvent->condvar;
 
    # do something such as adding a timer
-   # or socket watcher the calls $result_ready->broadcast
+   # or socket watcher the calls $result_ready->send
    # when the "result" is ready.
+   # in this case, we simply use a timer:
+   my $w = AnyEvent->timer (
+      after => 1,
+      cb    => sub { $result_ready->send },
+   );
+
+   # this "blocks" (while handling events) till the callback
+   # calls send
+   $result_ready->recv;
+
+Example: wait for a timer, but take advantage of the fact that
+condition variables are also code references.
+
+   my $done = AnyEvent->condvar;
+   my $delay = AnyEvent->timer (after => 5, cb => $done);
+   $done->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.
 
-   $result_ready->wait;
+=over 4
 
-=back
+=item $cv->send (...)
 
-=head2 SIGNAL WATCHERS
+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.
 
-You can listen for signals using a signal watcher, C<signal> is the signal
-I<name> without any C<SIG> prefix. Multiple signals events can be clumped
-together into one callback invocation, and callback invocation might or
-might not be asynchronous.
+If a callback has been set on the condition variable, it is called
+immediately from within send.
 
-These watchers might use C<%SIG>, so programs overwriting those signals
-directly will likely not work correctly.
+Any arguments passed to the C<send> call will be returned by all
+future C<< ->recv >> calls.
 
-Example: exit on SIGINT
+Condition variables are overloaded so one can call them directly
+(as a code reference). Calling them directly is the same as calling
+C<send>. Note, however, that many C-based event loops do not handle
+overloading, so as tempting as it may be, passing a condition variable
+instead of a callback does not work. Both the pure perl and EV loops
+support overloading, however, as well as all functions that use perl to
+invoke a callback (as in L<AnyEvent::Socket> and L<AnyEvent::DNS> for
+example).
 
-   my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
+=item $cv->croak ($error)
 
-=head2 CHILD PROCESS WATCHERS
+Similar to send, but causes all call's 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.
+
+=item $cv->begin ([group callback])
 
-You can also listen for the status of a child process specified by the
-C<pid> argument. The watcher will only trigger once. This works by
-installing a signal handler for C<SIGCHLD>.
+=item $cv->end
 
-Example: wait for pid 1333
+These two methods are EXPERIMENTAL and MIGHT CHANGE.
 
-  my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
+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.
 
-=head1 GLOBALS
+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. That callback
+is I<supposed> to call C<< ->send >>, but that is not required. If no
+callback was set, C<send> will be called without any arguments.
+
+Let's clarify this with the ping example:
+
+   my $cv = AnyEvent->condvar;
+
+   my %result;
+   $cv->begin (sub { $cv->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 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
+
+=item $cv->recv
+
+Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak
+>> methods have been called on c<$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.
+
+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
+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 supporting blocking waits if the caller so desires).
+
+Another reason I<never> to C<< ->recv >> in a module is that you cannot
+sensibly have two C<< ->recv >>'s in parallel, as that would require
+multiple interpreters or coroutines/threads, none of which C<AnyEvent>
+can supply.
+
+The L<Coro> module, however, I<can> and I<does> supply coroutines and, in
+fact, L<Coro::AnyEvent> replaces AnyEvent's condvars by coroutine-safe
+versions and also integrates coroutines into AnyEvent, making blocking
+C<< ->recv >> calls perfectly safe as long as they are done from another
+coroutine (one that doesn't run the event loop).
+
+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 ([new callback])
+
+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. Calling C<recv> inside the callback or at any later time
+is guaranteed not to block.
+
+=back
+
+=head1 GLOBAL VARIABLES AND FUNCTIONS
 
 =over 4
 
@@ -197,49 +618,206 @@
 
 The known classes so far are:
 
-   AnyEvent::Impl::Coro      based on Coro::Event, best choise.
-   AnyEvent::Impl::Event     based on Event, also best choice :)
-   AnyEvent::Impl::Glib      based on Glib, second-best choice.
+   AnyEvent::Impl::EV        based on EV (an interface to libev, best choice).
+   AnyEvent::Impl::Event     based on Event, second best choice.
+   AnyEvent::Impl::Perl      pure-perl implementation, fast and portable.
+   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.
+   AnyEvent::Impl::Qt        based on Qt, cannot be autoprobed (see its docs).
+   AnyEvent::Impl::EventLib  based on Event::Lib, leaks memory and worse.
+   AnyEvent::Impl::POE       based on POE, not generic enough for full support.
+
+There is no support for WxWidgets, as 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. Likewise, other POE backends can be used by AnyEvent by using
+it's adaptor.
+
+AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
+autodetecting them.
 
 =item AnyEvent::detect
 
-Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if
-necessary. You should only call this function right before you would have
-created an AnyEvent watcher anyway, that is, very late at runtime.
+Returns C<$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.
+
+=item $guard = AnyEvent::post_detect { BLOCK }
+
+Arranges for the code block to be executed as soon as the event model is
+autodetected (or immediately if this has already happened).
+
+If called in scalar or list context, then it creates and returns an object
+that automatically removes the callback again when it is destroyed. See
+L<Coro::BDB> for a case where this is useful.
+
+=item @AnyEvent::post_detect
+
+If there are any code references in this array (you can C<push> to it
+before or after loading AnyEvent), then they will called directly after
+the event loop has been chosen.
+
+You should check C<$AnyEvent::MODEL> before adding to this array, though:
+if it contains a true value then the event loop has already been detected,
+and the array will be ignored.
+
+Best use C<AnyEvent::post_detect { BLOCK }> instead.
 
 =back
 
 =head1 WHAT TO DO IN A MODULE
 
-As a module author, you should "use AnyEvent" and call AnyEvent methods
+As a module author, you should C<use AnyEvent> and call AnyEvent methods
 freely, but you should not load a specific event module or rely on it.
 
-Be careful when you create watchers in the module body - Anyevent will
+Be careful when you create watchers in the module body - AnyEvent will
 decide which event module to use as soon as the first method is called, so
 by calling AnyEvent in your module body you force the user of your module
 to load the event module first.
 
+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<< ->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<< ->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 and let AnyEvent decide which implementation to chose.
+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 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.
+
+You can chose to use a pure-perl implementation by loading the
+C<AnyEvent::Impl::Perl> 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;
 
-If the main program relies on a specific event model (for example, in Gtk2
-programs you have to rely on either Glib or Glib::Event), you should load
-it before loading AnyEvent or any module that uses it, generally, 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.
-
-You can chose to use a rather inefficient pure-perl implementation by
-loading the C<AnyEvent::Impl::Perl> module, but letting AnyEvent chose is
-generally better.
+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 and can therefore be mixed easily with other AnyEvent modules
+in the same program. Some of the modules come with AnyEvent, some are
+available via CPAN.
+
+=over 4
+
+=item L<AnyEvent::Util>
+
+Contains various utility functions that replace often-used but blocking
+functions such as C<inet_aton> by 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.
+
+=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.
+
+=item L<AnyEvent::DNS>
+
+Provides rich asynchronous DNS resolver capabilities.
+
+=item L<AnyEvent::HTTP>
+
+A simple-to-use HTTP library that is capable of making a lot of concurrent
+HTTP requests.
+
+=item L<AnyEvent::HTTPD>
+
+Provides a simple web application server framework.
+
+=item L<AnyEvent::FastPing>
+
+The fastest ping in the west.
+
+=item L<AnyEvent::DBI>
+
+Executes L<DBI> requests asynchronously in a proxy process.
+
+=item L<AnyEvent::AIO>
+
+Truly asynchronous I/O, should be in the toolbox of every event
+programmer. AnyEvent::AIO transparently fuses L<IO::AIO> and AnyEvent
+together.
+
+=item L<AnyEvent::BDB>
+
+Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently fuses
+L<BDB> and AnyEvent together.
+
+=item L<AnyEvent::GPSD>
+
+A non-blocking interface to gpsd, a daemon delivering GPS information.
+
+=item L<AnyEvent::IGS>
+
+A non-blocking interface to the Internet Go Server protocol (used by
+L<App::IGS>).
+
+=item L<Net::IRC3>
+
+AnyEvent based IRC client module family.
+
+=item L<Net::XMPP2>
+
+AnyEvent based XMPP (Jabber protocol) module family.
+
+=item L<Net::FCP>
+
+AnyEvent-based implementation of the Freenet Client Protocol, birthplace
+of AnyEvent.
+
+=item L<Event::ExecFlow>
+
+High level API for event-based execution flow control.
+
+=item L<Coro>
+
+Has special support for AnyEvent via L<Coro::AnyEvent>.
+
+=item L<IO::Lambda>
+
+The lambda approach to I/O - don't ask, look there. Can use AnyEvent.
+
+=back
 
 =cut
 
@@ -247,64 +825,129 @@
 
 no warnings;
 use strict;
+
 use Carp;
 
-our $VERSION = '2.51';
+our $VERSION = 4.2;
 our $MODEL;
 
 our $AUTOLOAD;
 our @ISA;
 
+our @REGISTRY;
+
+our $WIN32;
+
+BEGIN {
+   my $win32 = ! ! ($^O =~ /mswin32/i);
+   eval "sub WIN32(){ $win32 }";
+}
+
 our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
 
-our @REGISTRY;
+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";
+}
 
 my @models = (
-   [Coro::Event::          => AnyEvent::Impl::Coro::],
+   [EV::                   => AnyEvent::Impl::EV::],
    [Event::                => AnyEvent::Impl::Event::],
-   [Glib::                 => AnyEvent::Impl::Glib::],
-   [Tk::                   => AnyEvent::Impl::Tk::],
    [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
+   # everything below here will not be autoprobed
+   # as the pureperl backend should work everywhere
+   # and is usually faster
+   [Tk::                   => AnyEvent::Impl::Tk::],       # crashes with many handles
+   [Glib::                 => AnyEvent::Impl::Glib::],     # becomes extremely slow with many watchers
+   [Event::Lib::           => AnyEvent::Impl::EventLib::], # too buggy
+   [Qt::                   => AnyEvent::Impl::Qt::],       # requires special main program
+   [POE::Kernel::          => AnyEvent::Impl::POE::],      # lasciate ogni speranza
+   [Wx::                   => AnyEvent::Impl::POE::],
+   [Prima::                => AnyEvent::Impl::POE::],
 );
 
-our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);
+our %method = map +($_ => 1), qw(io timer time now signal child condvar one_event DESTROY);
+
+our @post_detect;
+
+sub post_detect(&) {
+   my ($cb) = @_;
+
+   if ($MODEL) {
+      $cb->();
+
+      1
+   } else {
+      push @post_detect, $cb;
+
+      defined wantarray
+         ? bless \$cb, "AnyEvent::Util::PostDetect"
+         : ()
+   }
+}
+
+sub AnyEvent::Util::PostDetect::DESTROY {
+   @post_detect = grep $_ != ${$_[0]}, @post_detect;
+}
 
 sub detect() {
    unless ($MODEL) {
       no strict 'refs';
+      local $SIG{__DIE__};
 
-      # check for already loaded models
-      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 $verbose > 1;
-               last;
-            }
+      if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) {
+         my $model = "AnyEvent::Impl::$1";
+         if (eval "require $model") {
+            $MODEL = $model;
+            warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1;
+         } else {
+            warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
          }
       }
 
+      # check for already loaded models
       unless ($MODEL) {
-         # try to load a model
-
          for (@REGISTRY, @models) {
             my ($package, $model) = @$_;
-            if (eval "require $package"
-                and ${"$package\::VERSION"} > 0
-                and eval "require $model") {
-               $MODEL = $model;
-               warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
-               last;
+            if (${"$package\::VERSION"} > 0) {
+               if (eval "require $model") {
+                  $MODEL = $model;
+                  warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
+                  last;
+               }
             }
          }
 
-         $MODEL
-           or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Event (or Coro+Event), Glib or Tk.";
+         unless ($MODEL) {
+            # try to load a model
+
+            for (@REGISTRY, @models) {
+               my ($package, $model) = @$_;
+               if (eval "require $package"
+                   and ${"$package\::VERSION"} > 0
+                   and eval "require $model") {
+                  $MODEL = $model;
+                  warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
+                  last;
+               }
+            }
+
+            $MODEL
+              or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib.";
+         }
       }
 
-      unshift @ISA, $MODEL;
       push @{"$MODEL\::ISA"}, "AnyEvent::Base";
+
+      unshift @ISA, $MODEL;
+
+      require AnyEvent::Strict if $ENV{PERL_ANYEVENT_STRICT};
+
+      (shift @post_detect)->() while @post_detect;
    }
 
    $MODEL
@@ -324,18 +967,17 @@
 
 package AnyEvent::Base;
 
-# default implementation for ->condvar, ->wait, ->broadcast
+# default implementation for now and time
 
-sub condvar {
-   bless \my $flag, "AnyEvent::Base::CondVar"
-}
+use Time::HiRes ();
 
-sub AnyEvent::Base::CondVar::broadcast {
-   ${$_[0]}++;
-}
+sub time { Time::HiRes::time }
+sub now  { Time::HiRes::time }
 
-sub AnyEvent::Base::CondVar::wait {
-   AnyEvent->one_event while !${$_[0]};
+# default implementation for ->condvar
+
+sub condvar {
+   bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, AnyEvent::CondVar::
 }
 
 # default implementation for ->signal
@@ -361,39 +1003,51 @@
 
    delete $SIG_CB{$signal}{$cb};
 
-   $SIG{$signal} = 'DEFAULT' unless keys %{ $SIG_CB{$signal} };
+   delete $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
 }
 
 # default implementation for ->child
 
 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)) {
-      $_->() for values %{ (delete $PID_CB{$pid}) || {} };
+      $_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
+                         (values %{ $PID_CB{0}    || {} });
    }
 
    undef $PID_IDLE;
 }
 
+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;
+   });
+}
+
 sub child {
    my (undef, %arg) = @_;
 
-   my $pid = uc $arg{pid}
+   defined (my $pid = $arg{pid} + 0)
       or Carp::croak "required option 'pid' is missing";
 
    $PID_CB{$pid}{$arg{cb}} = $arg{cb};
 
    unless ($WNOHANG) {
-      $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_child_wait);
-      $WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
+      $WNOHANG = eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
    }
 
-   # child could be a zombie already
-   $PID_IDLE ||= AnyEvent->timer (after => 0, cb => \&_child_wait);
+   unless ($CHLD_W) {
+      $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
+      # child could be a zombie already, so make at least one round
+      &_sigchld;
+   }
 
    bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
 }
@@ -407,63 +1061,211 @@
    undef $CHLD_W unless keys %PID_CB;
 }
 
+package AnyEvent::CondVar;
+
+our @ISA = AnyEvent::CondVar::Base::;
+
+package AnyEvent::CondVar::Base;
+
+use overload
+   '&{}'    => sub { my $self = shift; sub { $self->send (@_) } },
+   fallback => 1;
+
+sub _send {
+   # nop
+}
+
+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 {
+   $_[0]{_ae_sent}
+}
+
+sub _wait {
+   AnyEvent->one_event while !$_[0]{_ae_sent};
+}
+
+sub recv {
+   $_[0]->_wait;
+
+   Carp::croak $_[0]{_ae_croak} if $_[0]{_ae_croak};
+   wantarray ? @{ $_[0]{_ae_sent} } : $_[0]{_ae_sent}[0]
+}
+
+sub cb {
+   $_[0]{_ae_cb} = $_[1] if @_ > 1;
+   $_[0]{_ae_cb}
+}
+
+sub begin {
+   ++$_[0]{_ae_counter};
+   $_[0]{_ae_end_cb} = $_[1] if @_ > 1;
+}
+
+sub end {
+   return if --$_[0]{_ae_counter};
+   &{ $_[0]{_ae_end_cb} || sub { $_[0]->send } };
+}
+
+# undocumented/compatibility with pre-3.4
+*broadcast = \&send;
+*wait      = \&_wait;
+
 =head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
 
+This is an advanced topic that you do not normally need to use AnyEvent in
+a module. This section is only of use to event loop authors who want to
+provide AnyEvent compatibility.
+
 If you need to support another event library which isn't directly
 supported by AnyEvent, you can supply your own interface to it by
 pushing, before the first watcher gets created, the package name of
 the event module and the package name of the interface to use onto
 C<@AnyEvent::REGISTRY>. You can do that before and even without loading
-AnyEvent.
+AnyEvent, so it is reasonably cheap.
 
 Example:
 
    push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::];
 
 This tells AnyEvent to (literally) use the C<urxvt::anyevent::>
-package/class when it finds the C<urxvt> package/module is loaded. When
-AnyEvent is loaded and asked to find a suitable event model, it will
-first check for the presence of urxvt.
-
-The class should provide implementations for all watcher types (see
-L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>
-(Source code) and so on for actual examples, use C<perldoc -m
-AnyEvent::Impl::Glib> to see the sources).
-
-The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
-uses the above line as-is. An interface isn't included in AnyEvent
-because it doesn't make sense outside the embedded interpreter inside
-I<rxvt-unicode>, and it is updated and maintained as part of the
+package/class when it finds the C<urxvt> package/module is already loaded.
+
+When AnyEvent is loaded and asked to find a suitable event model, it
+will first check for the presence of urxvt by trying to C<use> the
+C<urxvt::anyevent> module.
+
+The class should provide implementations for all watcher types. See
+L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
+and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
+see the sources.
+
+If you don't provide C<signal> and C<child> watchers than AnyEvent will
+provide suitable (hopefully) replacements.
+
+The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
+terminal emulator uses the above line as-is. An interface isn't included
+in AnyEvent because it doesn't make sense outside the embedded interpreter
+inside I<rxvt-unicode>, and it is updated and maintained as part of the
 I<rxvt-unicode> distribution.
 
 I<rxvt-unicode> also cheats a bit by not providing blocking access to
 condition variables: code blocking while waiting for a condition will
 C<die>. This still works with most modules/usages, and blocking calls must
-not be in an interactive appliation, so it makes sense.
+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, reports which event
-model gets used.
+=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.
+
+=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 thoroughly check the arguments passed to most
+method calls and croaks if it finds any problems. In other words, enables
+"strict" mode.  Unlike C<use strict> it is definitely recommended ot keep
+it off in production.
+
+=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 must be a string consisting
+entirely of ASCII letters. The string C<AnyEvent::Impl::> gets prepended
+and the resulting module name is loaded and if the load was successful,
+used as event model. If it fails to load AnyEvent will proceed with
+auto detection and -probing.
+
+This functionality might change in future versions.
+
+For example, to force the pure perl model (L<AnyEvent::Impl::Perl>) you
+could start your program like this:
 
-=head1 EXAMPLE
+   PERL_ANYEVENT_MODEL=Perl perl ...
 
-The following program uses an io watcher to read data from stdin, a timer
-to display a message once per second, and a condvar to exit the program
-when the user enters quit:
+=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 connection errors already-
+
+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.
+
+=back
+
+=head1 EXAMPLE PROGRAM
+
+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:
 
    use AnyEvent;
 
    my $cv = AnyEvent->condvar;
 
-   my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
-      warn "io event <$_[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
-   });
+   my $io_watcher = AnyEvent->io (
+      fh   => \*STDIN,
+      poll => 'r',
+      cb   => sub {
+         warn "io event <$_[0]>\n";   # will always output <r>
+         chomp (my $input = <STDIN>); # read a line
+         warn "read: $input\n";       # output what has been read
+         $cv->send if $input =~ /^q/i; # quit program if /^q/i
+      },
+   );
 
    my $time_watcher; # can only be used once
 
@@ -476,7 +1278,7 @@
 
    new_timer; # create first timer
 
-   $cv->wait; # wait until user enters /^q/i
+   $cv->recv; # wait until user enters /^q/i
 
 =head1 REAL-WORLD EXAMPLE
 
@@ -536,13 +1338,13 @@
    $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
    }
 
@@ -550,12 +1352,12 @@
 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
-wether an exception as thrown (it is stored inside the $txn object)
+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
 random callback.
@@ -566,7 +1368,7 @@
 
    my $data = $fcp->client_get ($url);
 
-2. Blocking, but parallelizing:
+2. Blocking, but running in parallel:
 
    my @datas = map $_->result,
                   map $fcp->txn_client_get ($_),
@@ -575,9 +1377,9 @@
 Both blocking examples work without the module user having to know
 anything about events.
 
-3a. Event-based in a main program, using any support Event module:
+3a. Event-based in a main program, using any supported event module:
 
-   use Event;
+   use EV;
 
    $fcp->txn_client_get ($url)->cb (sub {
       my $txn = shift;
@@ -585,7 +1387,7 @@
       ...
    });
 
-   Event::loop;
+   EV::loop;
 
 3b. The module user could use AnyEvent, too:
 
@@ -595,20 +1397,345 @@
 
    $fcp->txn_client_get ($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.
+
+=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   400000   244   0.56   0.46    0.31 EV native interface
+        EV/Any   100000   244   2.50   0.46    0.29 EV + AnyEvent watchers
+    CoroEV/Any   100000   244   2.49   0.44    0.29 coroutines + Coro::Signal
+      Perl/Any   100000   513   4.92   0.87    1.12 pure perl implementation
+   Event/Event    16000   516  31.88  31.30    0.85 Event native interface
+     Event/Any    16000   590  35.75  31.42    1.08 Event + AnyEvent watchers
+      Glib/Any    16000  1357  98.22  12.41   54.00 quadratic behaviour
+        Tk/Any     2000  1860  26.97  67.98   14.00 SEGV with >> 2000 watchers
+     POE/Event     2000  6644 108.64 736.02   14.73 via POE::Loop::Event
+    POE/Select     2000  6343  94.13 809.12  565.96 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. Even when going through AnyEvent, it 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<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.
+
+=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  69.01    11.16 
+    Perl   20000  73.32    35.87 
+   Event   20000 212.62   257.32 
+    Glib   20000 651.16  1896.30 
+     POE   20000 349.67 12317.24 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.
+
+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
+
+
+=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. Only L<EV> is fully fork-aware.
+
+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.
+
+
+=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_ANYEGENT_STRICT}.
+
+
+=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
+mamleaks, such as leaking on C<map> and C<grep> but it is usually not as
+pronounced).
+
 
 =head1 SEE ALSO
 
-Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.
+Utility functions: L<AnyEvent::Util>.
+
+Event modules: 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>.
+
+Non-blocking file handles, sockets, TCP clients and
+servers: L<AnyEvent::Handle>, L<AnyEvent::Socket>.
+
+Asynchronous DNS: L<AnyEvent::DNS>.
+
+Coroutine support: L<Coro>, L<Coro::AnyEvent>, L<Coro::EV>, L<Coro::Event>,
+
+Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>, L<AnyEvent::DNS>.
 
-Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.
 
-Nontrivial usage example: L<Net::FCP>.
+=head1 AUTHOR
 
-=head1
+   Marc Lehmann <schmorp@schmorp.de>
+   http://home.schmorp.de/
 
 =cut