[ViewVC] Diff of: cvs/AnyEvent/lib/AnyEvent.pm

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.31 by root, Fri Nov 2 19:20:36 2007 UTC vs.
Revision 1.57 by root, Thu Apr 24 03:19:28 2008 UTC

 =head1 NAME
 AnyEvent - provide framework for multiple event loops
-Event, Coro, Glib, Tk, Perl - various supported event loops
+EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt - various supported event loops
 =head1 SYNOPSIS
    use AnyEvent;
    my $w = AnyEvent->timer (after => $seconds, cb => sub {
       ...
    });
-   my $w = AnyEvent->condvar; # stores wether a condition was flagged
+   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
+=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
+helps hiding 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 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.
+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).
+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
+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
+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).
-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
+During the first call of any watcher-creation method, the module tries
-loaded event loop by probing wether any of the following modules is
+to detect the currently loaded event loop by probing whether one of
-loaded: L<Coro::Event>, L<Event>, L<Glib>, L<Tk>. The first one found is
+the following modules is already loaded: L<Coro::EV>, L<Coro::Event>,
+L<EV>, L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>. The first one
-used. If none is found, the module tries to load these modules in the
+found is used. If none are found, the module tries to load these modules
-order given. The first one that could be successfully loaded will be
+(excluding Event::Lib and Qt) in the order given. The first one that can
-used. If still none could be found, AnyEvent will fall back to a pure-perl
+be successfully loaded will be used. If, after this, still none could be
-event loop, which is also not very efficient.
+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;
    use AnyEvent;
    # .. 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.
 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.
 These watchers are normal Perl objects with normal Perl lifetime. After
-creating a watcher it will immediately "watch" for events and invoke
+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).
-the callback. To disable the watcher you have to destroy it (e.g. by
+To disable the watcher you have to destroy it (e.g. by setting the
-setting the variable that stores it to C<undef> or otherwise deleting all
+variable you store it in to C<undef> or otherwise deleting all references
-references to it).
+to it).
 All watchers are created by calling a method on the C<AnyEvent> class.
+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:
+  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
-You can create I/O watcher by calling the C<< AnyEvent->io >> method with
+You can create an I/O watcher by calling the C<< AnyEvent->io >> method
-the following mandatory arguments:
+with the following mandatory key-value pairs as arguments:
-C<fh> the Perl I<filehandle> (not filedescriptor) to watch for
+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>, that creates
+events. C<poll> must be a string that is either C<r> or C<w>, which
-a watcher waiting for "r"eadable or "w"ritable events. C<cb> teh callback
+creates a watcher waiting for "r"eadable or "w"ritable events,
-to invoke everytime the filehandle becomes ready.
+respectively. C<cb> is the callback to invoke each time the file handle
+becomes ready.
-Only one io watcher per C<fh> and C<poll> combination is allowed (i.e. on
+As long as the I/O watcher exists it will keep the file descriptor or a
-a socket you can have one r + one w, not any more (limitation comes from
+copy of it alive/open.
-Tk - if you are sure you are not using Tk this limitation is gone).
-Filehandles will be kept alive, so as long as the watcher exists, the
+It is not allowed to close a file handle as long as any watcher is active
-filehandle exists, too.
+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:
    # wait for readability of STDIN, then read a line and disable the watcher
    my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
 =head2 TIME WATCHERS
 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
+C<after> specifies after how many seconds (fractional values are
-activate. C<cb> the callback to invoke.
+supported) should the timer activate. C<cb> 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).
    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;
+   my $cb = sub {
+      # cancel the old timer while creating a new one
+      $w = AnyEvent->timer (after => 1, cb => $cb);
+   };
+   # 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.
+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.
+AnyEvent always prefers relative timers, if available, matching the
+AnyEvent API.
+=head2 SIGNAL WATCHERS
+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.
+Multiple signals occurances 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.
+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).
+Example: wait for pid 1333
+  my $w = AnyEvent->child (
+     pid => 1333,
+     cb  => sub {
+        my ($pid, $status) = @_;
+        warn "pid $pid exited with status $status";
+     },
+  );
-=head2 CONDITION WATCHERS
+=head2 CONDITION VARIABLES
-Condition watchers can be created by calling the C<< AnyEvent->condvar >>
+Condition variables can be created by calling the C<< AnyEvent->condvar >>
 method without any arguments.
-A condition watcher watches for a condition - precisely that the C<<
+A condition variable waits for a condition - precisely that the C<<
 ->broadcast >> method has been called.
-The watcher has only two methods:
+They are very useful to signal that a condition has been fulfilled, 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.
+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.
+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
+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:
 =over 4
 =item $cv->wait
 Wait (blocking if necessary) until the C<< ->broadcast >> method has been
 called on c<$cv>, while servicing other watchers normally.
-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.
+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 suppporting 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 return after this method has been called. If nobody
+calls to C<wait> will (eventually) return after this method has been
-is waiting the broadcast will be remembered..
+called. If nobody is waiting the broadcast will be remembered..
+=back
 Example:
    # 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
    # when the "result" is ready.
+   # in this case, we simply use a timer:
+   my $w = AnyEvent->timer (
+      after => 1,
+      cb    => sub { $result_ready->broadcast },
+   );
+   # this "blocks" (while handling events) till the watcher
+   # calls broadcast
    $result_ready->wait;
-=back
+=head1 GLOBAL VARIABLES AND FUNCTIONS
-=head2 SIGNAL WATCHERS
-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.
-These watchers 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 listen for the status of a child process specified by the
-C<pid> argument (or any child if the pid argument is 0). The watcher will
-trigger as often as status change for the child are received. This works
-by installing a signal handler for C<SIGCHLD>.
-Example: wait for pid 1333
-  my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" });
-=head1 GLOBALS
 =over 4
 =item $AnyEvent::MODEL
 C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
 AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
 The known classes so far are:
-   EV::AnyEvent              based on EV (an interface to libev, best choice)
+   AnyEvent::Impl::CoroEV    based on Coro::EV, best choice.
-   AnyEvent::Impl::Coro      based on Coro::Event, second best choice.
+   AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
+   AnyEvent::Impl::EV        based on EV (an interface to libev, best choice).
-   AnyEvent::Impl::Event     based on Event, also second best choice :)
+   AnyEvent::Impl::Event     based on Event, second best choice.
-   AnyEvent::Impl::Glib      based on Glib, second-best choice.
+   AnyEvent::Impl::Glib      based on Glib, third-best choice.
    AnyEvent::Impl::Tk        based on Tk, very bad choice.
-   AnyEvent::Impl::Perl      pure-perl implementation, inefficient.
+   AnyEvent::Impl::Perl      pure-perl implementation, inefficient but portable.
+   AnyEvent::Impl::Qt        based on Qt, cannot be autoprobed (see its docs).
+   AnyEvent::Impl::EventLib  based on Event::Lib, leaks memory and worse.
 =item AnyEvent::detect
-Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model if
+Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
-necessary. You should only call this function right before you would have
+if necessary. You should only call this function right before you would
-created an AnyEvent watcher anyway, that is, very late at runtime.
+have created an AnyEvent watcher anyway, that is, as late as possible at
+runtime.
 =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<< ->wait >> on a condition variable unless you I<know> that
+the C<< ->broadcast >> 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
+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).
 =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
+If the main program relies on a specific event model. For example, in
-programs you have to rely on either Glib or Glib::Event), you should load
+Gtk2 programs you have to rely on the Glib module. You should load the
-it before loading AnyEvent or any module that uses it, generally, as early
+event module before loading AnyEvent or any module that uses it: generally
-as possible. The reason is that modules might create watchers when they
+speaking, you should load it as early as possible. The reason is that
-are loaded, and AnyEvent will decide on the event model to use as soon as
+modules might create watchers when they are loaded, and AnyEvent will
-it creates watchers, and it might chose the wrong one unless you load the
+decide on the event model to use as soon as it creates watchers, and it
-correct one yourself.
+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
+loading the C<AnyEvent::Impl::Perl> module, which gives you similar
-generally better.
+behaviour everywhere, but letting AnyEvent chose is generally better.
 =cut
 package AnyEvent;
 no warnings;
 use strict;
 use Carp;
-our $VERSION = '2.55';
+our $VERSION = '3.12';
 our $MODEL;
 our $AUTOLOAD;
 our @ISA;
 our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
 our @REGISTRY;
 my @models = (
+   [Coro::EV::             => AnyEvent::Impl::CoroEV::],
-   [Coro::Event::          => AnyEvent::Impl::Coro::],
+   [Coro::Event::          => AnyEvent::Impl::CoroEvent::],
-   [EV::                   => EV::AnyEvent::],
+   [EV::                   => AnyEvent::Impl::EV::],
    [Event::                => AnyEvent::Impl::Event::],
    [Glib::                 => AnyEvent::Impl::Glib::],
    [Tk::                   => AnyEvent::Impl::Tk::],
    [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
 );
+my @models_detect = (
+   [Qt::                   => AnyEvent::Impl::Qt::],       # requires special main program
+   [Event::Lib::           => AnyEvent::Impl::EventLib::], # too buggy
+);
-our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY);
+our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);
 sub detect() {
    unless ($MODEL) {
       no strict 'refs';
+      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 $verbose > 1;
+         }
+      }
       # check for already loaded models
+      unless ($MODEL) {
-      for (@REGISTRY, @models) {
+         for (@REGISTRY, @models, @models_detect) {
-         my ($package, $model) = @$_;
+            my ($package, $model) = @$_;
-         if (${"$package\::VERSION"} > 0) {
+            if (${"$package\::VERSION"} > 0) {
-            if (eval "require $model") {
+               if (eval "require $model") {
-               $MODEL = $model;
+                  $MODEL = $model;
-               warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1;
+                  warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
-               last;
+                  last;
+               }
             }
          }
-      }
-      unless ($MODEL) {
+         unless ($MODEL) {
-         # try to load a model
+            # try to load a model
-         for (@REGISTRY, @models) {
+            for (@REGISTRY, @models) {
-            my ($package, $model) = @$_;
+               my ($package, $model) = @$_;
-            if (eval "require $package"
+               if (eval "require $package"
-                and ${"$package\::VERSION"} > 0
+                   and ${"$package\::VERSION"} > 0
-                and eval "require $model") {
+                   and eval "require $model") {
-               $MODEL = $model;
+                  $MODEL = $model;
-               warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1;
+                  warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1;
-               last;
+                  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) or Glib.";
          }
-         $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.";
       }
       unshift @ISA, $MODEL;
       push @{"$MODEL\::ISA"}, "AnyEvent::Base";
    }
 # 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 %{ $PID_CB{$pid} || {} }),
+      $_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
-                 (values %{ $PID_CB{0}    || {} });
+                         (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 $CHLD_DELAY_W;
+      &_child_wait;
+   });
 }
 sub child {
    my (undef, %arg) = @_;
    unless ($WNOHANG) {
       $WNOHANG = eval { require POSIX; &POSIX::WNOHANG } || 1;
    }
    unless ($CHLD_W) {
-      $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_child_wait);
+      $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
-      # child could be a zombie already
+      # child could be a zombie already, so make at least one round
-      $PID_IDLE ||= AnyEvent->timer (after => 0, cb => \&_child_wait);
+      &_sigchld;
    }
    bless [$pid, $arg{cb}], "AnyEvent::Base::Child"
 }
    undef $CHLD_W unless keys %PID_CB;
 }
 =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
+package/class when it finds the C<urxvt> package/module is already loaded.
-AnyEvent is loaded and asked to find a suitable event model, it will
+When AnyEvent is loaded and asked to find a suitable event model, it
-first check for the presence of urxvt.
+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
+The class should provide implementations for all watcher types. See
-L<AnyEvent::Impl::Event> (source code), L<AnyEvent::Impl::Glib>
+L<AnyEvent::Impl::EV> (source code), L<AnyEvent::Impl::Glib> (Source code)
-(Source code) and so on for actual examples, use C<perldoc -m
+and so on for actual examples. Use C<perldoc -m AnyEvent::Impl::Glib> to
-AnyEvent::Impl::Glib> to see the sources).
+see the sources.
+If you don't provide C<signal> and C<child> watchers than AnyEvent will
+provide suitable (hopefully) replacements.
-The above isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
+The above example isn't fictitious, the I<rxvt-unicode> (a.k.a. urxvt)
-uses the above line as-is. An interface isn't included in AnyEvent
+terminal emulator uses the above line as-is. An interface isn't included
-because it doesn't make sense outside the embedded interpreter inside
+in AnyEvent because it doesn't make sense outside the embedded interpreter
-I<rxvt-unicode>, and it is updated and maintained as part of the
+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 application, 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
+=over 4
-model gets used.
+=item C<PERL_ANYEVENT_VERBOSE>
+When set to C<2> or higher, cause AnyEvent to report to STDERR which event
+model it chooses.
+=item C<PERL_ANYEVENT_MODEL>
+This can be used to specify the event model to be used by AnyEvent, before
+autodetection 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
+autodetection 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:
+  PERL_ANYEVENT_MODEL=Perl perl ...
+=back
-=head1 EXAMPLE
+=head1 EXAMPLE PROGRAM
-The following program uses an io watcher to read data from stdin, a timer
+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
+to display a message once per second, and a condition variable to quit the
-when the user enters quit:
+program when the user enters quit:
    use AnyEvent;
    my $cv = AnyEvent->condvar;
-   my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
+   my $io_watcher = AnyEvent->io (
+      fh   => \*STDIN,
+      poll => 'r',
+      cb   => sub {
-      warn "io event <$_[0]>\n";   # will always output <r>
+         warn "io event <$_[0]>\n";   # will always output <r>
-      chomp (my $input = <STDIN>); # read a line
+         chomp (my $input = <STDIN>); # read a line
-      warn "read: $input\n";       # output what has been read
+         warn "read: $input\n";       # output what has been read
-      $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i
+         $cv->broadcast 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 {
    $txn->{finished}->wait;
    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)
+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.
 All of this enables the following usage styles:
 1. Blocking:
    my $data = $fcp->client_get ($url);
-2. Blocking, but parallelizing:
+2. Blocking, but running in parallel:
    my @datas = map $_->result,
                   map $fcp->txn_client_get ($_),
                      @urls;
 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;
       my $data = $txn->result;
       ...
    });
-   Event::loop;
+   EV::loop;
 3b. The module user could use AnyEvent, too:
    use AnyEvent;
       $quit->broadcast;
    });
    $quit->wait;
+=head1 FORK
+Most event libraries are not fork-safe. The ones who are usually are
+because they are so inefficient. Only L<EV> is fully fork-aware.
+If you have to fork, you must either do so I<before> creating your first
+watcher OR you must not use AnyEvent at all in the child.
+=head1 SECURITY CONSIDERATIONS
+AnyEvent can be forced to load any event model via
+$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;
 =head1 SEE ALSO
-Event modules: L<Coro::Event>, L<Coro>, L<Event>, L<Glib::Event>, L<Glib>.
+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>,
+L<Event::Lib>, L<Qt>.
+Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
-Implementations: L<AnyEvent::Impl::Coro>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>, L<AnyEvent::Impl::Tk>.
+L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
+L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
+L<AnyEvent::Impl::Qt>.
-Nontrivial usage example: L<Net::FCP>.
+Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
-=head1
+=head1 AUTHOR
+ Marc Lehmann <schmorp@schmorp.de>
+ http://home.schmorp.de/
 =cut
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Revision 1.57 by root, Thu Apr 24 03:19:28 2008 UTC