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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.60 by root, Fri Apr 25 01:05:26 2008 UTC vs.
Revision 1.89 by root, Fri Apr 25 14:19:23 2008 UTC

 =head1 NAME
 AnyEvent - provide framework for multiple event loops
-EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt - various supported event loops
+EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops
 =head1 SYNOPSIS
    use AnyEvent;
 The interface itself is vaguely similar, but not identical to the L<Event>
 module.
 During the first call of any watcher-creation method, the module tries
-to detect the currently loaded event loop by probing whether one of
+to detect the currently loaded event loop by probing whether one of the
-the following modules is already loaded: L<Coro::EV>, L<Coro::Event>,
+following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
-L<EV>, L<Event>, L<Glib>, L<Tk>, L<Event::Lib>, L<Qt>. The first one
+L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
-found is used. If none are found, the module tries to load these modules
+L<POE>. The first one found is used. If none are found, the module tries
-(excluding Event::Lib and Qt) in the order given. The first one that can
+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
 Note that C<my $w; $w => combination. This is necessary because in Perl,
 my variables are only visible after the statement in which they are
 declared.
-=head2 IO WATCHERS
+=head2 I/O WATCHERS
 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
+C<fh> the Perl I<file handle> (I<not> file descriptor) to watch
-events. C<poll> must be a string that is either C<r> or C<w>, which
+for events. C<poll> must be a string that is either C<r> or C<w>,
-creates a watcher waiting for "r"eadable or "w"ritable events,
+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.
-As long as the I/O watcher exists it will keep the file descriptor or a
+Although the callback might get passed parameters, their value and
-copy of it alive/open.
+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.
-It is not allowed to close a file handle as long as any watcher is active
+You must not close a file handle as long as any watcher is active on the
-on the underlying file descriptor.
+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.
 You can create a time watcher by calling the C<< AnyEvent->timer >>
 method with the following mandatory arguments:
 C<after> specifies after how many seconds (fractional values are
-supported) should the timer activate. C<cb> the callback to invoke in that
+supported) the callback should be invoked. C<cb> is the callback to invoke
-case.
+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 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).
 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.
+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 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 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).
+and exit status (as returned by waitpid), so unlike other watcher types,
+you I<can> rely on child watcher callback arguments.
-Example: wait for pid 1333
+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;
+  AnyEvent::detect; # force event module to be initialised
+  my $pid = fork or exit 5;
   my $w = AnyEvent->child (
-     pid => 1333,
+     pid => $pid,
      cb  => sub {
         my ($pid, $status) = @_;
         warn "pid $pid exited with status $status";
+        $done->broadcast;
      },
   );
+  # do something else, then wait for process exit
+  $done->wait;
 =head2 CONDITION VARIABLES
 Condition variables can be created by calling the C<< AnyEvent->condvar >>
 method without any arguments.
    AnyEvent::Impl::CoroEV    based on Coro::EV, best choice.
    AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice.
    AnyEvent::Impl::EV        based on EV (an interface to libev, best choice).
    AnyEvent::Impl::Event     based on Event, second best choice.
    AnyEvent::Impl::Glib      based on Glib, third-best choice.
+   AnyEvent::Impl::Perl      pure-perl implementation, inefficient but portable.
    AnyEvent::Impl::Tk        based on Tk, very bad choice.
-   AnyEvent::Impl::Perl      pure-perl implementation, inefficient but portable.
    AnyEvent::Impl::Qt        based on Qt, cannot be autoprobed (see its docs).
    AnyEvent::Impl::EventLib  based on Event::Lib, leaks memory and worse.
+   AnyEvent::Impl::POE       based on POE, not generic enough for full support.
+There is no support for WxWidgets, as WxWidgets has no support for
+watching file handles. However, you can use WxWidgets through the
+POE Adaptor, as POE has a Wx backend that simply polls 20 times per
+second, which was considered to be too horrible to even consider for
+AnyEvent. Likewise, other POE backends can be used by AnyEvent by using
+it's adaptor.
+AnyEvent knows about L<Prima> and L<Wx> and will try to use L<POE> when
+autodetecting them.
 =item AnyEvent::detect
 Returns C<$AnyEvent::MODEL>, forcing autodetection of the event model
 if necessary. You should only call this function right before you would
 no warnings;
 use strict;
 use Carp;
-our $VERSION = '3.2';
+our $VERSION = '3.3';
 our $MODEL;
 our $AUTOLOAD;
 our @ISA;
    [Coro::Event::          => AnyEvent::Impl::CoroEvent::],
    [EV::                   => AnyEvent::Impl::EV::],
    [Event::                => AnyEvent::Impl::Event::],
    [Glib::                 => AnyEvent::Impl::Glib::],
    [Tk::                   => AnyEvent::Impl::Tk::],
+   [Wx::                   => AnyEvent::Impl::POE::],
+   [Prima::                => AnyEvent::Impl::POE::],
    [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::],
-);
+   # everything below here will not be autoprobed as the pureperl backend should work everywhere
-my @models_detect = (
+   [Event::Lib::           => AnyEvent::Impl::EventLib::], # too buggy
    [Qt::                   => AnyEvent::Impl::Qt::],       # requires special main program
-   [Event::Lib::           => AnyEvent::Impl::EventLib::], # too buggy
+   [POE::Kernel::          => AnyEvent::Impl::POE::],      # lasciate ogni speranza
 );
 our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY);
 sub detect() {
          }
       }
       # check for already loaded models
       unless ($MODEL) {
-         for (@REGISTRY, @models, @models_detect) {
+         for (@REGISTRY, @models) {
             my ($package, $model) = @$_;
             if (${"$package\::VERSION"} > 0) {
                if (eval "require $model") {
                   $MODEL = $model;
                   warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1;
 =back
 =head1 EXAMPLE PROGRAM
-The following program uses an IO watcher to read data from STDIN, a timer
+The following program uses an I/O watcher to read data from STDIN, a timer
 to display a message once per second, and a condition variable to quit the
 program when the user enters quit:
    use AnyEvent;
       $quit->broadcast;
    });
    $quit->wait;
+=head1 BENCHMARK
+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), here is a benchmark of various supported
+event models natively and with 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.
+Rewriting the benchmark to use many different sockets instead of using
+the same filehandle for all I/O watchers results in a much longer runtime
+(socket creation is expensive), but qualitatively the same figures, so it
+was not used.
+=head2 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<< ->broadcast >> 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.
+=head2 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   936  39.17  33.63    1.43 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
+=head2 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.
+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 on the third place.
+C<Glib>'s memory usage is quite a bit 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: 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 this, as session creation overhead is small compared
+to execution of the state machine, which is coded pretty optimally within
+L<AnyEvent::Impl::POE>. POE simply seems to be abysmally slow.
+=head2 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 simply avoid POE like the plague if you want performance or
+reasonable memory usage.
+=back
 =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
   BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
   use AnyEvent;
 =head1 SEE ALSO
 Event modules: L<Coro::EV>, L<EV>, L<EV::Glib>, L<Glib::EV>,
 L<Coro::Event>, L<Event>, L<Glib::Event>, L<Glib>, L<Coro>, L<Tk>,
-L<Event::Lib>, L<Qt>.
+L<Event::Lib>, L<Qt>, L<POE>.
 Implementations: L<AnyEvent::Impl::CoroEV>, L<AnyEvent::Impl::EV>,
 L<AnyEvent::Impl::CoroEvent>, L<AnyEvent::Impl::Event>, L<AnyEvent::Impl::Glib>,
 L<AnyEvent::Impl::Tk>, L<AnyEvent::Impl::Perl>, L<AnyEvent::Impl::EventLib>,
-L<AnyEvent::Impl::Qt>.
+L<AnyEvent::Impl::Qt>, L<AnyEvent::Impl::POE>.
 Nontrivial usage examples: L<Net::FCP>, L<Net::XMPP2>.
 =head1 AUTHOR
  Marc Lehmann <schmorp@schmorp.de>
  http://home.schmorp.de/

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.60 by root, Fri Apr 25 01:05:26 2008 UTC vs. Revision 1.89 by root, Fri Apr 25 14:19:23 2008 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.60 by root, Fri Apr 25 01:05:26 2008 UTC vs.
Revision 1.89 by root, Fri Apr 25 14:19:23 2008 UTC