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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.232 by root, Thu Jul 9 01:08:22 2009 UTC vs.
Revision 1.253 by root, Tue Jul 21 06:00:47 2009 UTC

 =head1 NAME
-AnyEvent - provide framework for multiple event loops
+AnyEvent - events independent of event loop implementation
 EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
 event loops.
 =head1 SYNOPSIS
 =head1 INTRODUCTION/TUTORIAL
 This manpage is mainly a reference manual. If you are interested
 in a tutorial or some gentle introduction, have a look at the
 L<AnyEvent::Intro> manpage.
+=head1 SUPPORT
+There is a mailinglist for discussing all things AnyEvent, and an IRC
+channel, too.
+See the AnyEvent project page at the B<Schmorpforge Ta-Sa Software
+Respository>, at L<http://anyevent.schmorp.de>, for more info.
 =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?
 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.
+between multiple watchers, and AnyEvent will ensure that signals will not
+interrupt your program at bad times.
-This watcher might use C<%SIG>, so programs overwriting those signals
+This watcher might use C<%SIG> (depending on the event loop used),
-directly will likely not work correctly.
+so programs overwriting those signals directly will likely not work
+correctly.
 Example: exit on SIGINT
    my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
+=head3 Signal Races, Delays and Workarounds
+Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
+callbacks to signals in a generic way, which is a pity, as you cannot do
+race-free signal handling in perl. AnyEvent will try to do it's best, but
+in some cases, signals will be delayed. The maximum time a signal might
+be delayed is specified in C<$AnyEvent::MAX_SIGNAL_LATENCY> (default: 10
+seconds). This variable can be changed only before the first signal
+watcher is created, and should be left alone otherwise. Higher values
+will cause fewer spurious wake-ups, which is better for power and CPU
+saving. All these problems can be avoided by installing the optional
+L<Async::Interrupt> module. This will not work with inherently broken
+event loops such as L<Event> or L<Event::Lib> (and not with L<POE>
+currently, as POE does it's own workaround with one-second latency). With
+those, you just have to suffer the delays.
 =head2 CHILD PROCESS WATCHERS
 You can also watch on a child process exit and catch its exit status.
 This means you cannot create a child watcher as the very first
 thing in an AnyEvent program, you I<have> to create at least one
 watcher before you C<fork> the child (alternatively, you can call
 C<AnyEvent::detect>).
+As most event loops do not support waiting for child events, they will be
+emulated by AnyEvent in most cases, in which the latency and race problems
+mentioned in the description of signal watchers apply.
 Example: fork a process and wait for it
    my $done = AnyEvent->condvar;
 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
+AnyEvent is slightly different: it expects somebody else to run the event
-will only block when necessary (usually when told by the user).
+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.
+Now is probably a good time to look at the examples further below.
 Condition variables can be created by calling the C<< AnyEvent->condvar
 >> method, usually without arguments. The only argument pair allowed is
 C<cb>, which specifies a callback to be called when the condition variable
 becomes true, with the condition variable as the first argument (but not
 the results).
 After creation, the condition variable is "false" until it becomes "true"
 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.
+a result. And yet some people know them as "futures" - a promise to
+compute/deliver something that you can wait for.
 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
       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
+Example: wait for a timer, but take advantage of the fact that condition
-condition variables are also code references.
+variables are also callable directly.
    my $done = AnyEvent->condvar;
    my $delay = AnyEvent->timer (after => 5, cb => $done);
    $done->recv;
    ...
    my @info = $couchdb->info->recv;
-And this is how you would just ste a callback to be called whenever the
+And this is how you would just set a callback to be called whenever the
 results are available:
    $couchdb->info->cb (sub {
       my @info = $_[0]->recv;
    });
 immediately from within send.
 Any arguments passed to the C<send> call will be returned by all
 future C<< ->recv >> calls.
-Condition variables are overloaded so one can call them directly
+Condition variables are overloaded so one can call them directly (as if
-(as a code reference). Calling them directly is the same as calling
+they were a code reference). Calling them directly is the same as calling
-C<send>. Note, however, that many C-based event loops do not handle
+C<send>.
-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).
 =item $cv->croak ($error)
 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.
+user/consumer. Doing it this way instead of calling C<croak> directly
+delays the error detetcion, but has the overwhelmign advantage that it
+diagnoses the error at the place where the result is expected, and not
+deep in some event clalback without connection to the actual code causing
+the problem.
 =item $cv->begin ([group callback])
 =item $cv->end
 function will call C<croak>.
 In list context, all parameters passed to C<send> will be returned,
 in scalar context only the first one will be returned.
+Note that doing a blocking wait in a callback is not supported by any
+event loop, that is, recursive invocation of a blocking C<< ->recv
+>> is not allowed, and the C<recv> call will C<croak> if such a
+condition is detected. This condition can be slightly loosened by using
+L<Coro::AnyEvent>, which allows you to do a blocking C<< ->recv >> from
+any thread that doesn't run the event loop itself.
 Not all event models support a blocking wait - some die in that case
 (programs might want to do that to stay interactive), so I<if you are
-using this from a module, never require a blocking wait>, but let the
+using this from a module, never require a blocking wait>. Instead, let the
 caller decide whether the call will block or not (for example, by coupling
 condition variables with some kind of request results and supporting
 callbacks so the caller knows that getting the result will not block,
 while still 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.
 =back
 =head1 GLOBAL VARIABLES AND FUNCTIONS
+These are not normally required to use AnyEvent, but can be useful to
+write AnyEvent extension modules.
 =over 4
 =item $AnyEvent::MODEL
-Contains C<undef> until the first watcher is being created. Then it
+Contains C<undef> until the first watcher is being created, before the
+backend has been autodetected.
-contains the event model that is being used, which is the name of the
+Afterwards it contains the event model that is being used, which is the
-Perl class implementing the model. This class is usually one of the
+name of the Perl class implementing the model. This class is usually one
-C<AnyEvent::Impl:xxx> modules, but can be any other class in the case
+of the C<AnyEvent::Impl:xxx> modules, but can be any other class in the
-AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode>).
+case AnyEvent has been extended at runtime (e.g. in I<rxvt-unicode> it
+will be C<urxvt::anyevent>).
 =item AnyEvent::detect
 Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
 if necessary. You should only call this function right before you would
 have created an AnyEvent watcher anyway, that is, as late as possible at
-runtime.
+runtime, and not e.g. while initialising of your module.
+If you need to do some initialisation before AnyEvent watchers are
+created, use C<post_detect>.
 =item $guard = AnyEvent::post_detect { BLOCK }
 Arranges for the code block to be executed as soon as the event model is
 autodetected (or immediately if this has already happened).
+The block will be executed I<after> the actual backend has been detected
+(C<$AnyEvent::MODEL> is set), but I<before> any watchers have been
+created, so it is possible to e.g. patch C<@AnyEvent::ISA> or do
+other initialisations - see the sources of L<AnyEvent::Strict> or
+L<AnyEvent::AIO> to see how this is used.
+The most common usage is to create some global watchers, without forcing
+event module detection too early, for example, L<AnyEvent::AIO> creates
+and installs the global L<IO::AIO> watcher in a C<post_detect> block to
+avoid autodetecting the event module at load time.
 If called in scalar or list context, then it creates and returns an object
-that automatically removes the callback again when it is destroyed. See
+that automatically removes the callback again when it is destroyed (or
+C<undef> when the hook was immediately executed). See L<AnyEvent::AIO> for
-L<Coro::BDB> for a case where this is useful.
+a case where this is useful.
+Example: Create a watcher for the IO::AIO module and store it in
+C<$WATCHER>. Only do so after the event loop is initialised, though.
+   our WATCHER;
+   my $guard = AnyEvent::post_detect {
+      $WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
+   };
+   # the ||= is important in case post_detect immediately runs the block,
+   # as to not clobber the newly-created watcher. assigning both watcher and
+   # post_detect guard to the same variable has the advantage of users being
+   # able to just C<undef $WATCHER> if the watcher causes them grief.
+   $WATCHER ||= $guard;
 =item @AnyEvent::post_detect
 If there are any code references in this array (you can C<push> to it
 before or after loading AnyEvent), then they will called directly after
 the event loop has been chosen.
 You should check C<$AnyEvent::MODEL> before adding to this array, though:
-if it contains a true value then the event loop has already been detected,
+if it is defined then the event loop has already been detected, and the
-and the array will be ignored.
+array will be ignored.
-Best use C<AnyEvent::post_detect { BLOCK }> instead.
+Best use C<AnyEvent::post_detect { BLOCK }> when your application allows
+it,as it takes care of these details.
+This variable is mainly useful for modules that can do something useful
+when AnyEvent is used and thus want to know when it is initialised, but do
+not need to even load it by default. This array provides the means to hook
+into AnyEvent passively, without loading it.
 =back
 =head1 WHAT TO DO IN A MODULE
 =cut
 package AnyEvent;
+# basically a tuned-down version of common::sense
+sub common_sense {
-no warnings;
+   # no warnings
+   ${^WARNING_BITS} ^= ${^WARNING_BITS};
-use strict qw(vars subs);
+   # use strict vars subs
+   $^H |= 0x00000600;
+}
+BEGIN { AnyEvent::common_sense }
-use Carp;
+use Carp ();
-our $VERSION = 4.801;
+our $VERSION = 4.86;
 our $MODEL;
 our $AUTOLOAD;
 our @ISA;
 our @REGISTRY;
 our $WIN32;
+our $VERBOSE;
 BEGIN {
    eval "sub WIN32(){ " . (($^O =~ /mswin32/i)*1) ." }";
    eval "sub TAINT(){ " . (${^TAINT}*1) . " }";
    delete @ENV{grep /^PERL_ANYEVENT_/, keys %ENV}
       if ${^TAINT};
-}
-our $verbose = $ENV{PERL_ANYEVENT_VERBOSE}*1;
+   $VERBOSE = $ENV{PERL_ANYEVENT_VERBOSE}*1;
+}
+our $MAX_SIGNAL_LATENCY = 10;
 our %PROTOCOL; # (ipv4|ipv6) => (1|2), higher numbers are preferred
 {
    my $idx;
    # as the pureperl backend should work everywhere
    # and is usually faster
    [Glib::                 => AnyEvent::Impl::Glib::],     # becomes extremely slow with many watchers
    [Event::Lib::           => AnyEvent::Impl::EventLib::], # too buggy
    [Tk::                   => AnyEvent::Impl::Tk::],       # crashes with many handles
+   [Qt::                   => AnyEvent::Impl::Qt::],       # requires special main program
    [POE::Kernel::          => AnyEvent::Impl::POE::],      # lasciate ogni speranza
-   [Qt::                   => AnyEvent::Impl::Qt::],       # requires special main program
    [Wx::                   => AnyEvent::Impl::POE::],
    [Prima::                => AnyEvent::Impl::POE::],
    # IO::Async is just too broken - we would need workarounds for its
    # byzantine signal and broken child handling, among others.
    # IO::Async is rather hard to detect, as it doesn't have any
    my ($cb) = @_;
    if ($MODEL) {
       $cb->();
-      1
+      undef
    } else {
       push @post_detect, $cb;
       defined wantarray
          ? bless \$cb, "AnyEvent::Util::postdetect"
    @post_detect = grep $_ != ${$_[0]}, @post_detect;
 }
 sub detect() {
    unless ($MODEL) {
-      no strict 'refs';
       local $SIG{__DIE__};
       if ($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 $verbose > 1;
+            warn "AnyEvent: loaded model '$model' (forced by \$ENV{PERL_ANYEVENT_MODEL}), using it.\n" if $VERBOSE >= 2;
          } else {
-            warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose;
+            warn "AnyEvent: unable to load model '$model' (from \$ENV{PERL_ANYEVENT_MODEL}):\n$@" if $VERBOSE;
          }
       }
       # check for already loaded models
       unless ($MODEL) {
          for (@REGISTRY, @models) {
             my ($package, $model) = @$_;
             if (${"$package\::VERSION"} > 0) {
                if (eval "require $model") {
                   $MODEL = $model;
-                  warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
+                  warn "AnyEvent: autodetected model '$model', using it.\n" if $VERBOSE >= 2;
                   last;
                }
             }
          }
                my ($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 $verbose > 1;
+                  warn "AnyEvent: autoprobed model '$model', using it.\n" if $VERBOSE >= 2;
                   last;
                }
             }
             $MODEL
 sub AUTOLOAD {
    (my $func = $AUTOLOAD) =~ s/.*://;
    $method{$func}
-      or croak "$func: not a valid method for AnyEvent objects";
+      or Carp::croak "$func: not a valid method for AnyEvent objects";
    detect unless $MODEL;
    my $class = shift;
    $class->$func (@_);
 # allow only one watcher per fd, so we dup it to get a different one).
 sub _dupfh($$;$$) {
    my ($poll, $fh, $r, $w) = @_;
    # cygwin requires the fh mode to be matching, unix doesn't
-   my ($rw, $mode) = $poll eq "r" ? ($r, "<") : ($w, ">");
+   my ($rw, $mode) = $poll eq "r" ? ($r, "<&") : ($w, ">&");
-   open my $fh2, "$mode&", $fh
+   open my $fh2, $mode, $fh
       or die "AnyEvent->io: cannot dup() filehandle in mode '$poll': $!,";
    # we assume CLOEXEC is already set by perl in all important cases
    ($fh2, $rw)
 package AnyEvent::Base;
 # default implementations for many methods
-BEGIN {
+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())...
    } else {
+      warn "AnyEvent: using built-in time(), WARNING, no sub-second resolution!\n" if $VERBOSE;
       *_time = sub { time }; # epic fail
    }
+   &_time
 }
 sub time { _time }
 sub now  { _time }
 sub now_update { }
    bless { @_ == 3 ? (_ae_cb => $_[2]) : () }, "AnyEvent::CondVar"
 }
 # default implementation for ->signal
+our $HAVE_ASYNC_INTERRUPT;
 our ($SIGPIPE_R, $SIGPIPE_W, %SIG_CB, %SIG_EV, $SIG_IO);
+our (%SIG_ASY, %SIG_ASY_W);
+our ($SIG_COUNT, $SIG_TW);
 sub _signal_exec {
+   $HAVE_ASYNC_INTERRUPT
+      ? $SIGPIPE_R->drain
-   sysread $SIGPIPE_R, my $dummy, 4;
+      : sysread $SIGPIPE_R, my $dummy, 9;
    while (%SIG_EV) {
       for (keys %SIG_EV) {
          delete $SIG_EV{$_};
          $_->() for values %{ $SIG_CB{$_} || {} };
       }
    }
 }
+# install a dumym wakeupw atcher 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;
+      $SIG_TW = AnyEvent->timer (
+         after    => $MAX_SIGNAL_LATENCY - ($NOW - int $NOW),
+         interval => $MAX_SIGNAL_LATENCY,
+         cb       => sub { }, # just for the PERL_ASYNC_CHECK
+      );
+   }
+}
+sub _sig_del {
+   undef $SIG_TW
+      unless --$SIG_COUNT;
+}
+sub _signal {
+   my (undef, %arg) = @_;
+   my $signal = uc $arg{signal}
+      or Carp::croak "required option 'signal' is missing";
+   $SIG_CB{$signal}{$arg{cb}} = $arg{cb};
+   if ($HAVE_ASYNC_INTERRUPT) {
+      # async::interrupt
+      $SIG_ASY{$signal} ||= do {
+         my $asy = new Async::Interrupt
+            cb     => sub { undef $SIG_EV{$signal} },
+            signal => $signal,
+            pipe   => [$SIGPIPE_R->filenos],
+         ;
+         $asy->pipe_autodrain (0);
+         $asy
+      };
+   } else {
+      # pure perl
+      $SIG{$signal} ||= sub {
+         local $!;
+         syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
+         undef $SIG_EV{$signal};
+      };
+      # can't do signal processing without introducing races in pure perl,
+      # so limit the signal latency.
+      _sig_add;
+   }
+   bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
+}
 sub signal {
-   my (undef, %arg) = @_;
+   # probe for availability of Async::Interrupt
+   if (!$ENV{PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT} && eval "use Async::Interrupt 0.6 (); 1") {
+      warn "AnyEvent: using Async::Interrupt for race-free signal handling.\n" if $VERBOSE >= 8;
-   unless ($SIGPIPE_R) {
+      $HAVE_ASYNC_INTERRUPT = 1;
+      $SIGPIPE_R = new Async::Interrupt::EventPipe;
+      $SIG_IO = AnyEvent->io (fh => $SIGPIPE_R->fileno, poll => "r", cb => \&_signal_exec);
+   } else {
+      warn "AnyEvent: using emulated perl signal handling with latency timer.\n" if $VERBOSE >= 8;
       require Fcntl;
       if (AnyEvent::WIN32) {
          require AnyEvent::Util;
          or Carp::croak "AnyEvent: unable to create a signal reporting pipe: $!\n";
       $SIG_IO = AnyEvent->io (fh => $SIGPIPE_R, poll => "r", cb => \&_signal_exec);
    }
-   my $signal = uc $arg{signal}
+   *signal = \&_signal;
-      or Carp::croak "required option 'signal' is missing";
+   &signal
-   $SIG_CB{$signal}{$arg{cb}} = $arg{cb};
-   $SIG{$signal} ||= sub {
-      local $!;
-      syswrite $SIGPIPE_W, "\x00", 1 unless %SIG_EV;
-      undef $SIG_EV{$signal};
-   };
-   bless [$signal, $arg{cb}], "AnyEvent::Base::signal"
 }
 sub AnyEvent::Base::signal::DESTROY {
    my ($signal, $cb) = @{$_[0]};
+   _sig_del;
    delete $SIG_CB{$signal}{$cb};
+   $HAVE_ASYNC_INTERRUPT
+      ? delete $SIG_ASY{$signal}
-   # delete doesn't work with older perls - they then
+      : # delete doesn't work with older perls - they then
-   # print weird messages, or just unconditionally exit
+        # print weird messages, or just unconditionally exit
-   # instead of getting the default action.
+        # instead of getting the default action.
+        undef $SIG{$signal}
-   undef $SIG{$signal} unless keys %{ $SIG_CB{$signal} };
+      unless keys %{ $SIG_CB{$signal} };
 }
 # default implementation for ->child
 our %PID_CB;
 our $CHLD_DELAY_W;
 our $WNOHANG;
 sub _sigchld {
    while (0 < (my $pid = waitpid -1, $WNOHANG)) {
+      $_->($pid, $?)
-      $_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }),
+         for values %{ $PID_CB{$pid} || {} },
-                         (values %{ $PID_CB{0}    || {} });
+             values %{ $PID_CB{0}    || {} };
    }
 }
 sub child {
    my (undef, %arg) = @_;
    defined (my $pid = $arg{pid} + 0)
       or Carp::croak "required option 'pid' is missing";
    $PID_CB{$pid}{$arg{cb}} = $arg{cb};
+   # WNOHANG is almost cetrainly 1 everywhere
+   $WNOHANG ||= $^O =~ /^(?:openbsd|netbsd|linux|freebsd|cygwin|MSWin32)$/
+                ? 1
-   $WNOHANG ||= eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
+                : eval { local $SIG{__DIE__}; require POSIX; &POSIX::WNOHANG } || 1;
    unless ($CHLD_W) {
       $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld);
       # child could be a zombie already, so make at least one round
       &_sigchld;
 our @ISA = AnyEvent::CondVar::Base::;
 package AnyEvent::CondVar::Base;
-use overload
+#use overload
-   '&{}'    => sub { my $self = shift; sub { $self->send (@_) } },
+#   '&{}'    => sub { my $self = shift; sub { $self->send (@_) } },
-   fallback => 1;
+#   fallback => 1;
+# save 300+ kilobytes by dirtily hardcoding overloading
+${"AnyEvent::CondVar::Base::OVERLOAD"}{dummy}++; # Register with magic by touching.
+*{'AnyEvent::CondVar::Base::()'}   = sub { }; # "Make it findable via fetchmethod."
+*{'AnyEvent::CondVar::Base::(&{}'} = sub { my $self = shift; sub { $self->send (@_) } }; # &{}
+${'AnyEvent::CondVar::Base::()'}   = 1; # fallback
+our $WAITING;
 sub _send {
    # nop
 }
 sub ready {
    $_[0]{_ae_sent}
 }
 sub _wait {
+   $WAITING
+      and !$_[0]{_ae_sent}
+      and Carp::croak "AnyEvent::CondVar: recursive blocking wait detected";
+   local $WAITING = 1;
    AnyEvent->one_event while !$_[0]{_ae_sent};
 }
 sub recv {
    $_[0]->_wait;
 C<PERL_ANYEVENT_MODEL>.
 When set to C<2> or higher, cause AnyEvent to report to STDERR which event
 model it chooses.
+When set to C<8> or higher, then AnyEvent will report extra information on
+which optional modules it loads and how it implements certain features.
 =item C<PERL_ANYEVENT_STRICT>
 AnyEvent does not do much argument checking by default, as thorough
 argument checking is very costly. Setting this variable to a true value
 will cause AnyEvent to load C<AnyEvent::Strict> and then to thoroughly
 check the arguments passed to most method calls. If it finds any problems,
 it will croak.
 In other words, enables "strict" mode.
-Unlike C<use strict>, it is definitely recommended to keep it off in
+Unlike C<use strict> (or it's modern cousin, C<< use L<common::sense>
-production. Keeping C<PERL_ANYEVENT_STRICT=1> in your environment while
+>>, it is definitely recommended to keep it off in production. Keeping
-developing programs can be very useful, however.
+C<PERL_ANYEVENT_STRICT=1> in your environment while developing programs
+can be very useful, however.
 =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
 When neither C<ca_file> nor C<ca_path> was specified during
 L<AnyEvent::TLS> context creation, and either of these environment
 variables exist, they will be used to specify CA certificate locations
 instead of a system-dependent default.
+=item C<PERL_ANYEVENT_AVOID_GUARD> and C<PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT>
+When these are set to C<1>, then the respective modules are not
+loaded. Mostly good for testing AnyEvent itself.
 =back
 =head1 SUPPLYING YOUR OWN EVENT MODEL INTERFACE
 A handler for C<SIGCHLD> is installed by AnyEvent's child watcher
 emulation for event loops that do not support them natively. Also, some
 event loops install a similar handler.
-If, when AnyEvent is loaded, SIGCHLD is set to IGNORE, then AnyEvent will
+Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE, then
-reset it to default, to avoid losing child exit statuses.
+AnyEvent will reset it to default, to avoid losing child exit statuses.
 =item SIGPIPE
 A no-op handler is installed for C<SIGPIPE> when C<$SIG{PIPE}> is C<undef>
 when AnyEvent gets loaded.
    if $SIG{CHLD} eq 'IGNORE';
 $SIG{PIPE} = sub { }
    unless defined $SIG{PIPE};
+=head1 RECOMMENDED/OPTIONAL MODULES
+One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
+it's built-in modules) are required to use it.
+That does not mean that AnyEvent won't take advantage of some additional
+modules if they are installed.
+This section epxlains which additional modules will be used, and how they
+affect AnyEvent's operetion.
+=over 4
+=item L<Async::Interrupt>
+This slightly arcane module is used to implement fast signal handling: To
+my knowledge, there is no way to do completely race-free and quick
+signal handling in pure perl. To ensure that signals still get
+delivered, AnyEvent will start an interval timer to wake up perl (and
+catch the signals) with some delay (default is 10 seconds, look for
+C<$AnyEvent::MAX_SIGNAL_LATENCY>).
+If this module is available, then it will be used to implement signal
+catching, which means that signals will not be delayed, and the event loop
+will not be interrupted regularly, which is more efficient (And good for
+battery life on laptops).
+This affects not just the pure-perl event loop, but also other event loops
+that have no signal handling on their own (e.g. Glib, Tk, Qt).
+Some event loops (POE, Event, Event::Lib) offer signal watchers natively,
+and either employ their own workarounds (POE) or use AnyEvent's workaround
+(using C<$AnyEvent::MAX_SIGNAL_LATENCY>). Installing L<Async::Interrupt>
+does nothing for those backends.
+=item L<EV>
+This module isn't really "optional", as it is simply one of the backend
+event loops that AnyEvent can use. However, it is simply the best event
+loop available in terms of features, speed and stability: It supports
+the AnyEvent API optimally, implements all the watcher types in XS, does
+automatic timer adjustments even when no monotonic clock is available,
+can take avdantage of advanced kernel interfaces such as C<epoll> and
+C<kqueue>, and is the fastest backend I<by far>. You can even embed
+L<Glib>/L<Gtk2> in it (or vice versa, see L<EV::Glib> and L<Glib::EV>).
+=item L<Guard>
+The guard module, when used, will be used to implement
+C<AnyEvent::Util::guard>. This speeds up guards considerably (and uses a
+lot less memory), but otherwise doesn't affect guard operation much. It is
+purely used for performance.
+=item L<JSON> and L<JSON::XS>
+This module is required when you want to read or write JSON data 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.
+=item L<Net::SSLeay>
+Implementing TLS/SSL in Perl is certainly interesting, but not very
+worthwhile: If this module is installed, then L<AnyEvent::Handle> (with
+the help of L<AnyEvent::TLS>), gains the ability to do TLS/SSL.
+=item L<Time::HiRes>
+This module is part of perl since release 5.008. It will be used when the
+chosen event library does not come with a timing source on it's own. The
+pure-perl event loop (L<AnyEvent::Impl::Perl>) will additionally use it to
+try to use a monotonic clock for timing stability.
+=back
 =head1 FORK
 Most event libraries are not fork-safe. The ones who are usually are
 because they rely on inefficient but fork-safe C<select> or C<poll>
 calls. 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.
+watcher OR you must not use AnyEvent at all in the child OR you must do
+something completely out of the scope of AnyEvent.
 =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 1.232 by root, Thu Jul 9 01:08:22 2009 UTC vs.
Revision 1.253 by root, Tue Jul 21 06:00:47 2009 UTC