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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.266 by root, Thu Jul 30 03:41:56 2009 UTC vs.
Revision 1.303 by root, Sat Dec 5 02:52:03 2009 UTC

 might affect timers and time-outs.
 When this is the case, you can call this method, which will update the
 event loop's idea of "current time".
+A typical example would be a script in a web server (e.g. C<mod_perl>) -
+when mod_perl executes the script, then the event loop will have the wrong
+idea about the "current time" (being potentially far in the past, when the
+script ran the last time). In that case you should arrange a call to C<<
+AnyEvent->now_update >> each time the web server process wakes up again
+(e.g. at the start of your script, or in a handler).
 Note that updating the time I<might> cause some events to be handled.
 =back
 =head2 SIGNAL WATCHERS
 Example: exit on SIGINT
    my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
+=head3 Restart Behaviour
+While restart behaviour is up to the event loop implementation, most will
+not restart syscalls (that includes L<Async::Interrupt> and AnyEvent's
+pure perl implementation).
+=head3 Safe/Unsafe Signals
+Perl signals can be either "safe" (synchronous to opcode handling) or
+"unsafe" (asynchronous) - the former might get delayed indefinitely, the
+latter might corrupt your memory.
+AnyEvent signal handlers are, in addition, synchronous to the event loop,
+i.e. they will not interrupt your running perl program but will only be
+called as part of the normal event handling (just like timer, I/O etc.
+callbacks, too).
 =head3 Signal Races, Delays and Workarounds
 Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
-callbacks to signals in a generic way, which is a pity, as you cannot do
+callbacks to signals in a generic way, which is a pity, as you cannot
-race-free signal handling in perl. AnyEvent will try to do it's best, but
+do race-free signal handling in perl, requiring C libraries for
+this. AnyEvent will try to do it's best, which means in some cases,
-in some cases, signals will be delayed. The maximum time a signal might
+signals will be delayed. The maximum time a signal might be delayed is
-be delayed is specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10
+specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10 seconds). This
-seconds). This variable can be changed only before the first signal
+variable can be changed only before the first signal watcher is created,
-watcher is created, and should be left alone otherwise. Higher values
+and should be left alone otherwise. This variable determines how often
+AnyEvent polls for signals (in case a wake-up was missed). Higher values
 will cause fewer spurious wake-ups, which is better for power and CPU
+saving.
-saving. All these problems can be avoided by installing the optional
+All these problems can be avoided by installing the optional
-L<Async::Interrupt> module. This will not work with inherently broken
+L<Async::Interrupt> module, which works with most event loops. It will not
-event loops such as L<Event> or L<Event::Lib> (and not with L<POE>
+work with inherently broken event loops such as L<Event> or L<Event::Lib>
-currently, as POE does it's own workaround with one-second latency). With
+(and not with L<POE> currently, as POE does it's own workaround with
-those, you just have to suffer the delays.
+one-second latency). For those, you just have to suffer the delays.
 =head2 CHILD PROCESS WATCHERS
    $w = AnyEvent->child (pid => <process id>, cb => <callback>);
       after => 1,
       cb    => sub { $result_ready->send },
    );
    # this "blocks" (while handling events) till the callback
-   # calls -<send
+   # calls ->send
    $result_ready->recv;
 Example: wait for a timer, but take advantage of the fact that condition
 variables are also callable directly.
 one. For example, a function that pings many hosts in parallel might want
 to use a condition variable for the whole process.
 Every call to C<< ->begin >> will increment a counter, and every call to
 C<< ->end >> will decrement it.  If the counter reaches C<0> in C<< ->end
->>, the (last) callback passed to C<begin> will be executed. That callback
+>>, the (last) callback passed to C<begin> will be executed, passing the
-is I<supposed> to call C<< ->send >>, but that is not required. If no
+condvar as first argument. That callback is I<supposed> to call C<< ->send
-callback was set, C<send> will be called without any arguments.
+>>, but that is not required. If no group callback was set, C<send> will
+be called without any arguments.
 You can think of C<< $cv->send >> giving you an OR condition (one call
 sends), while C<< $cv->begin >> and C<< $cv->end >> giving you an AND
 condition (all C<begin> calls must be C<end>'ed before the condvar sends).
 begung can potentially be zero:
    my $cv = AnyEvent->condvar;
    my %result;
-   $cv->begin (sub { $cv->send (\%result) });
+   $cv->begin (sub { shift->send (\%result) });
    for my $host (@list_of_hosts) {
       $cv->begin;
       ping_host_then_call_callback $host, sub {
          $result{$host} = ...;
 =item $cb = $cv->cb ($cb->($cv))
 This is a mutator function that returns the callback set and optionally
 replaces it before doing so.
-The callback will be called when the condition becomes "true", i.e. when
+The callback will be called when the condition becomes (or already was)
-C<send> or C<croak> are called, with the only argument being the condition
+"true", i.e. when C<send> or C<croak> are called (or were called), with
-variable itself. Calling C<recv> inside the callback or at any later time
+the only argument being the condition variable itself. Calling C<recv>
-is guaranteed not to block.
+inside the callback or at any later time is guaranteed not to block.
 =back
 =head1 SUPPORTED EVENT LOOPS/BACKENDS
 =over 4
 =item Backends that are autoprobed when no other event loop can be found.
 EV is the preferred backend when no other event loop seems to be in
-use. If EV is not installed, then AnyEvent will try Event, and, failing
+use. If EV is not installed, then AnyEvent will fall back to its own
-that, will fall back to its own pure-perl implementation, which is
+pure-perl implementation, which is available everywhere as it comes with
-available everywhere as it comes with AnyEvent itself.
+AnyEvent itself.
    AnyEvent::Impl::EV        based on EV (interface to libev, best choice).
-   AnyEvent::Impl::Event     based on Event, very stable, few glitches.
    AnyEvent::Impl::Perl      pure-perl implementation, fast and portable.
 =item Backends that are transparently being picked up when they are used.
 These will be used when they are currently loaded when the first watcher
 is created, in which case it is assumed that the application is using
 them. This means that AnyEvent will automatically pick the right backend
 when the main program loads an event module before anything starts to
 create watchers. Nothing special needs to be done by the main program.
+   AnyEvent::Impl::Event     based on Event, very stable, few glitches.
    AnyEvent::Impl::Glib      based on Glib, slow but very stable.
    AnyEvent::Impl::Tk        based on Tk, very broken.
    AnyEvent::Impl::EventLib  based on Event::Lib, leaks memory and worse.
    AnyEvent::Impl::POE       based on POE, very slow, some limitations.
    AnyEvent::Impl::Irssi     used when running within irssi.
 package AnyEvent;
 # basically a tuned-down version of common::sense
 sub common_sense {
-   # no warnings
+   # from common:.sense 1.0
-   ${^WARNING_BITS} ^= ${^WARNING_BITS};
+   ${^WARNING_BITS} = "\xfc\x3f\x33\x00\x0f\xf3\xcf\xc0\xf3\xfc\x33\x03";
    # use strict vars subs
    $^H |= 0x00000600;
 }
 BEGIN { AnyEvent::common_sense }
 use Carp ();
-our $VERSION = 4.881;
+our $VERSION = '5.22';
 our $MODEL;
 our $AUTOLOAD;
 our @ISA;
 our @REGISTRY;
-our $WIN32;
 our $VERBOSE;
 BEGIN {
    eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
              $ENV{PERL_ANYEVENT_PROTOCOLS} || "ipv4,ipv6";
 }
 my @models = (
    [EV::                   => AnyEvent::Impl::EV::   , 1],
-   [Event::                => AnyEvent::Impl::Event::, 1],
    [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl:: , 1],
    # everything below here will not (normally) be autoprobed
    # as the pureperl backend should work everywhere
    # and is usually faster
+   [Event::                => AnyEvent::Impl::Event::, 1],
    [Glib::                 => AnyEvent::Impl::Glib:: , 1], # becomes extremely slow with many watchers
    [Event::Lib::           => AnyEvent::Impl::EventLib::], # too buggy
    [Irssi::                => AnyEvent::Impl::Irssi::],    # Irssi has a bogus "Event" package
    [Tk::                   => AnyEvent::Impl::Tk::],       # crashes with many handles
    [Qt::                   => AnyEvent::Impl::Qt::],       # requires special main program
    [Prima::                => AnyEvent::Impl::POE::],
    # IO::Async is just too broken - we would need workarounds for its
    # byzantine signal and broken child handling, among others.
    # IO::Async is rather hard to detect, as it doesn't have any
    # obvious default class.
-#   [0, IO::Async::            => AnyEvent::Impl::IOAsync::],  # requires special main program
+   [IO::Async::               => AnyEvent::Impl::IOAsync::], # requires special main program
-#   [0, IO::Async::Loop::      => AnyEvent::Impl::IOAsync::],  # requires special main program
+   [IO::Async::Loop::         => AnyEvent::Impl::IOAsync::], # requires special main program
-#   [0, IO::Async::Notifier::  => AnyEvent::Impl::IOAsync::],  # requires special main program
+   [IO::Async::Notifier::     => AnyEvent::Impl::IOAsync::], # requires special main program
+   [AnyEvent::Impl::IOAsync:: => AnyEvent::Impl::IOAsync::], # requires special main program
 );
 our %method = map +($_ => 1),
    qw(io timer time now now_update signal child idle condvar one_event DESTROY);
    # we assume CLOEXEC is already set by perl in all important cases
    ($fh2, $rw)
 }
+=head1 SIMPLIFIED AE API
+Starting with version 5.0, AnyEvent officially supports a second, much
+simpler, API that is designed to reduce the calling, typing and memory
+overhead.
+See the L<AE> manpage for details.
+=cut
+package AE;
+our $VERSION = $AnyEvent::VERSION;
+sub io($$$) {
+   AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
+}
+sub timer($$$) {
+   AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2])
+}
+sub signal($$) {
+   AnyEvent->signal (signal => $_[0], cb => $_[1])
+}
+sub child($$) {
+   AnyEvent->child (pid => $_[0], cb => $_[1])
+}
+sub idle($) {
+   AnyEvent->idle (cb => $_[0])
+}
+sub cv(;&) {
+   AnyEvent->condvar (@_ ? (cb => $_[0]) : ())
+}
+sub now() {
+   AnyEvent->now
+}
+sub now_update() {
+   AnyEvent->now_update
+}
+sub time() {
+   AnyEvent->time
+}
 package AnyEvent::Base;
 # default implementations for many methods
-sub _time {
+sub _time() {
    # probe for availability of Time::HiRes
    if (eval "use Time::HiRes (); Time::HiRes::time (); 1") {
       warn "AnyEvent: using Time::HiRes for sub-second timing accuracy.\n" if $VERBOSE >= 8;
       *_time = \&Time::HiRes::time;
       # if (eval "use POSIX (); (POSIX::times())...
 our $HAVE_ASYNC_INTERRUPT;
 sub _have_async_interrupt() {
    $HAVE_ASYNC_INTERRUPT = 1*(!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT}
-                              && eval "use Async::Interrupt 1.0 (); 1")
+                              && eval "use Async::Interrupt 1.02 (); 1")
       unless defined $HAVE_ASYNC_INTERRUPT;
    $HAVE_ASYNC_INTERRUPT
 }
 our ($SIG_COUNT, $SIG_TW);
 sub _signal_exec {
    $HAVE_ASYNC_INTERRUPT
       ? $SIGPIPE_R->drain
-      : sysread $SIGPIPE_R, my $dummy, 9;
+      : sysread $SIGPIPE_R, (my $dummy), 9;
    while (%SIG_EV) {
       for (keys %SIG_EV) {
          delete $SIG_EV{$_};
          $_->() for values %{ $SIG_CB{$_} || {} };
 # install a dummy wakeup watcher to reduce signal catching latency
 sub _sig_add() {
    unless ($SIG_COUNT++) {
       # try to align timer on a full-second boundary, if possible
-      my $NOW = AnyEvent->now;
+      my $NOW = AE::now;
-      $SIG_TW = AnyEvent->timer (
+      $SIG_TW = AE::timer
-         after    => $MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
+         $MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
-         interval => $MAX_SIGNAL_LATENCY,
+         $MAX_SIGNAL_LATENCY,
-         cb       => sub { }, # just for the PERL_ASYNC_CHECK
+         sub { } # just for the PERL_ASYNC_CHECK
-      );
+      ;
    }
 }
 sub _sig_del {
    undef $SIG_TW
       # probe for availability of Async::Interrupt
       if (_have_async_interrupt) {
          warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
          $SIGPIPE_R = new Async::Interrupt::EventPipe;
-         $SIG_IO = AnyEvent->io (fh => $SIGPIPE_R->fileno, poll => "r", cb => \&_signal_exec);
+         $SIG_IO = AE::io $SIGPIPE_R->fileno, 0, \&_signal_exec;
       } else {
          warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
          require Fcntl;
          }
          $SIGPIPE_R
             or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
-         $SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
+         $SIG_IO = AE::io $SIGPIPE_R, 0, \&_signal_exec;
       }
       *signal = sub {
          my (undef, %arg) = @_;
    $WNOHANG ||= $^O =~ /^(?:openbsd|netbsd|linux|freebsd|cygwin|MSWin32)$/
                 ? 1
                 : eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
    unless ($CHLD_W) {
-      $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
+      $CHLD_W = AE::signal CHLD => \&_sigchld;
       # child could be a zombie already, so make at least one round
       &_sigchld;
    }
    bless [$pid, $arg{cb}], "AnyEvent::Base::child"
          # never use more then 50% of the time for the idle watcher,
          # within some limits
          $w = 0.0001 if $w < 0.0001;
          $w = 5      if $w > 5;
-         $w = AnyEvent->timer (after => $w, cb => $rcb);
+         $w = AE::timer $w, 0, $rcb;
       } else {
          # clean up...
          undef $w;
          undef $rcb;
       }
    };
-   $w = AnyEvent->timer (after => 0.05, cb => $rcb);
+   $w = AE::timer 0.05, 0, $rcb;
    bless \\$cb, "AnyEvent::Base::idle"
 }
 sub AnyEvent::Base::idle::DESTROY {
    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;
+   my $cv = shift;
+   @_
+      and $cv->{_ae_cb} = shift
+      and $cv->{_ae_sent}
+      and (delete $cv->{_ae_cb})->($cv);
-   $_[0]{_ae_cb}
+   $cv->{_ae_cb}
 }
 sub begin {
    ++$_[0]{_ae_counter};
    $_[0]{_ae_end_cb} = $_[1] if @_ > 1;
 }
 # undocumented/compatibility with pre-3.4
 *broadcast = \&send;
 *wait      = \&_wait;
-#############################################################################
-# "new" API, currently only emulation of it
-#############################################################################
-package AE;
-sub io($$$) {
-   AnyEvent->io (fh => $_[0], poll => $_[1] ? "w" : "r", cb => $_[2])
-}
-sub timer($$$) {
-   AnyEvent->timer (after => $_[0], interval => $_[1], cb => $_[2]);
-}
-sub signal($$) {
-   AnyEvent->signal (signal => $_[0], cb => $_[1]);
-}
-sub child($$) {
-   AnyEvent->child (pid => $_[0], cb => $_[1]);
-}
-sub idle($) {
-   AnyEvent->idle (cb => $_[0]);
-}
-sub cv() {
-   AnyEvent->condvar
-}
-sub now() {
-   AnyEvent->now
-}
-sub now_update() {
-   AnyEvent->now_update
-}
-sub time() {
-   AnyEvent->time
-}
 =head1 ERROR AND EXCEPTION HANDLING
 In general, AnyEvent does not do any error handling - it relies on the
 caller to do that if required. The L<AnyEvent::Strict> module (see also
          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
-   sub new_timer {
-      $timer = AnyEvent->timer (after => 1, cb => sub {
+   my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
-         warn "timeout\n"; # print 'timeout' about every second
+      warn "timeout\n"; # print 'timeout' at most every second
-         &new_timer; # and restart the time
-      });
+   });
-   }
-   new_timer; # create first timer
    $cv->recv; # wait until user enters /^q/i
 =head1 REAL-WORLD EXAMPLE
 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.
+distribution. It uses the L<AE> interface, which makes a real difference
+for the EV and Perl backends only.
 =head3 Explanation of the columns
 I<watcher> is the number of event watchers created/destroyed. Since
 different event models feature vastly different performances, each event
 watcher.
 =head3 Results
           name watchers bytes create invoke destroy comment
-         EV/EV   400000   224   0.47   0.35    0.27 EV native interface
+         EV/EV   100000   223   0.47   0.43    0.27 EV native interface
-        EV/Any   100000   224   2.88   0.34    0.27 EV + AnyEvent watchers
+        EV/Any   100000   223   0.48   0.42    0.26 EV + AnyEvent watchers
-    CoroEV/Any   100000   224   2.85   0.35    0.28 coroutines + Coro::Signal
+  Coro::EV/Any   100000   223   0.47   0.42    0.26 coroutines + Coro::Signal
-      Perl/Any   100000   452   4.13   0.73    0.95 pure perl implementation
+      Perl/Any   100000   431   2.70   0.74    0.92 pure perl implementation
-   Event/Event    16000   517  32.20  31.80    0.81 Event native interface
+   Event/Event    16000   516  31.16  31.84    0.82 Event native interface
-     Event/Any    16000   590  35.85  31.55    1.06 Event + AnyEvent watchers
+     Event/Any    16000  1203  42.61  34.79    1.80 Event + AnyEvent watchers
-   IOAsync/Any    16000   989  38.10  32.77   11.13 via IO::Async::Loop::IO_Poll
+   IOAsync/Any    16000  1911  41.92  27.45   16.81 via IO::Async::Loop::IO_Poll
-   IOAsync/Any    16000   990  37.59  29.50   10.61 via IO::Async::Loop::Epoll
+   IOAsync/Any    16000  1726  40.69  26.37   15.25 via IO::Async::Loop::Epoll
-      Glib/Any    16000  1357 102.33  12.31   51.00 quadratic behaviour
+      Glib/Any    16000  1118  89.00  12.57   51.17 quadratic behaviour
-        Tk/Any     2000  1860  27.20  66.31   14.00 SEGV with >> 2000 watchers
+        Tk/Any     2000  1346  20.96  10.75    8.00 SEGV with >> 2000 watchers
-     POE/Event     2000  6328 109.99 751.67   14.02 via POE::Loop::Event
+       POE/Any     2000  6951 108.97 795.32   14.24 via POE::Loop::Event
-    POE/Select     2000  6027  94.54 809.13  579.80 via POE::Loop::Select
+       POE/Any     2000  6648  94.79 774.40  575.51 via POE::Loop::Select
 =head3 Discussion
 The benchmark does I<not> measure scalability of the event loop very
 well. For example, a select-based event loop (such as the pure perl one)
 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
+maximal/minimal, respectively. When using the L<AE> API there is zero
+overhead (when going through the AnyEvent API create is about 5-6 times
+slower, with other times being equal, so still uses far less memory than
-far less memory than any other event loop and is still faster than Event
+any other event loop and is still faster than Event natively).
-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
 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.
+distribution. It uses the L<AE> interface, which makes a real difference
+for the EV and Perl backends only.
 =head3 Explanation of the columns
 I<sockets> is the number of sockets, and twice the number of "servers" (as
 each server has a read and write socket end).
 a new one that moves the timeout into the future.
 =head3 Results
      name sockets create  request
-       EV   20000  69.01    11.16
+       EV   20000  62.66     7.99
-     Perl   20000  73.32    35.87
+     Perl   20000  68.32    32.64
-  IOAsync   20000 157.00    98.14 epoll
+  IOAsync   20000 174.06   101.15 epoll
-  IOAsync   20000 159.31   616.06 poll
+  IOAsync   20000 174.67   610.84 poll
-    Event   20000 212.62   257.32
+    Event   20000 202.69   242.91
-     Glib   20000 651.16  1896.30
+     Glib   20000 557.01  1689.52
-      POE   20000 349.67 12317.24 uses POE::Loop::Event
+      POE   20000 341.54 12086.32 uses POE::Loop::Event
 =head3 Discussion
 This benchmark I<does> measure scalability and overall performance of the
 particular event loop.
 As you can see, the AnyEvent + EV combination even beats the
 hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
 backend easily beats IO::Lambda and POE.
 And even the 100% non-blocking version written using the high-level (and
-slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda by a
+slow :) L<AnyEvent::Handle> abstraction beats both POE and IO::Lambda
-large margin, even though it does all of DNS, tcp-connect and socket I/O
+higher level ("unoptimised") abstractions by a large margin, even though
-in a non-blocking way.
+it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
 The two AnyEvent benchmarks programs can be found as F<eg/ae0.pl> and
 F<eg/ae2.pl> in the AnyEvent distribution, the remaining benchmarks are
-part of the IO::lambda distribution and were used without any changes.
+part of the IO::Lambda distribution and were used without any changes.
 =head1 SIGNALS
 AnyEvent currently installs handlers for these signals:
 it's built-in modules) are required to use it.
 That does not mean that AnyEvent won't take advantage of some additional
 modules if they are installed.
-This section epxlains which additional modules will be used, and how they
+This section explains which additional modules will be used, and how they
-affect AnyEvent's operetion.
+affect AnyEvent's operation.
 =over 4
 =item L<Async::Interrupt>
 catch the signals) with some delay (default is 10 seconds, look for
 C<$AnyEvent::MAX_SIGNAL_LATENCY>).
 If this module is available, then it will be used to implement signal
 catching, which means that signals will not be delayed, and the event loop
-will not be interrupted regularly, which is more efficient (And good for
+will not be interrupted regularly, which is more efficient (and good for
 battery life on laptops).
 This affects not just the pure-perl event loop, but also other event loops
 that have no signal handling on their own (e.g. Glib, Tk, Qt).
 lot less memory), but otherwise doesn't affect guard operation much. It is
 purely used for performance.
 =item L<JSON> and L<JSON::XS>
-This module is required when you want to read or write JSON data via
+One of these modules is required when you want to read or write JSON data
-L<AnyEvent::Handle>. It is also written in pure-perl, but can take
+via L<AnyEvent::Handle>. It is also written in pure-perl, but can take
 advantage of the ultra-high-speed L<JSON::XS> module when it is installed.
 In fact, L<AnyEvent::Handle> will use L<JSON::XS> by default if it is
 installed.
 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.
+This means that, in general, you cannot fork and do event processing
+in the child if a watcher was created before the fork (which in turn
+initialises the event library).
 If you have to fork, you must either do so I<before> creating your first
 watcher OR you must not use AnyEvent at all in the child OR you must do
 something completely out of the scope of AnyEvent.
+The problem of doing event processing in the parent I<and> the child
+is much more complicated: even for backends that I<are> fork-aware or
+fork-safe, their behaviour is not usually what you want: fork clones all
+watchers, that means all timers, I/O watchers etc. are active in both
+parent and child, which is almost never what you want.
 =head1 SECURITY CONSIDERATIONS
 AnyEvent can be forced to load any event model via

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.266 by root, Thu Jul 30 03:41:56 2009 UTC vs. Revision 1.303 by root, Sat Dec 5 02:52:03 2009 UTC

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Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.266 by root, Thu Jul 30 03:41:56 2009 UTC vs.
Revision 1.303 by root, Sat Dec 5 02:52:03 2009 UTC