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

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.72 by root, Fri Apr 25 07:43:25 2008 UTC vs.
Revision 1.81 by root, Fri Apr 25 13:05:17 2008 UTC

 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 the
 following modules is already loaded: L<Coro::EV>, L<Coro::Event>, L<EV>,
-L<Event>, L<Glib>, L<Tk>, L<AnyEvent::Impl::Perl>, L<Event::Lib>, L<Qt>,
+L<Event>, L<Glib>, L<AnyEvent::Impl::Perl>, L<Tk>, L<Event::Lib>, L<Qt>,
 L<POE>. The first one found is used. If none are found, the module tries
-to load these modules (excluding Event::Lib, Qt and POE as the pure perl
+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.
 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
    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
 =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;
 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 io watchers (watching STDOUT, a pty, to
+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
 I<destroy> is the time, in microseconds, that it takes to destroy a single
 watcher.
 =head2 Results
-          name watcher bytes create invoke destroy comment
+          name watchers bytes create invoke destroy comment
-         EV/EV  400000   244   0.56   0.46    0.31 EV native interface
+         EV/EV   400000   244   0.56   0.46    0.31 EV native interface
-        EV/Any  100000   610   3.52   0.91    0.75 EV + AnyEvent watchers
+        EV/Any   100000   610   3.52   0.91    0.75 EV + AnyEvent watchers
-    CoroEV/Any  100000   610   3.49   0.92    0.75 coroutines + Coro::Signal
+    CoroEV/Any   100000   610   3.49   0.92    0.75 coroutines + Coro::Signal
-      Perl/Any   16000   654   4.64   1.22    0.77 pure perl implementation
+      Perl/Any   100000   513   4.91   0.92    1.15 pure perl implementation
-   Event/Event   16000   523  28.05  21.38    0.86 Event native interface
+   Event/Event    16000   523  28.05  21.38    0.86 Event native interface
-     Event/Any   16000   943  34.43  20.48    1.39 Event + AnyEvent watchers
+     Event/Any    16000   943  34.43  20.48    1.39 Event + AnyEvent watchers
-      Glib/Any   16000  1357  96.99  12.55   55.51 quadratic behaviour
+      Glib/Any    16000  1357  96.99  12.55   55.51 quadratic behaviour
-        Tk/Any    2000  1855  27.01  66.61   14.03 SEGV with >> 2000 watchers
+        Tk/Any     2000  1855  27.01  66.61   14.03 SEGV with >> 2000 watchers
-     POE/Event    2000  6644 108.15 768.19   14.33 via POE::Loop::Event
+     POE/Event     2000  6644 108.15 768.19   14.33 via POE::Loop::Event
-    POE/Select    2000  6343  94.69 807.65  562.69 via POE::Loop::Select
+    POE/Select     2000  6343  94.69 807.65  562.69 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, only a single filehandle
+file descriptors grows high. In this benchmark, all events become ready at
-is used (although some of the AnyEvent adaptors dup() its file descriptor
+the same time, so select/poll-based implementations get an unnatural speed
-to worka round bugs).
+boost.
 C<EV> is the sole leader regarding speed and memory use, which are both
-maximal/minimal, respectively. Even when going through AnyEvent, there is
+maximal/minimal, respectively. Even when going through AnyEvent, there are
-only one event loop that uses less memory (the C<Event> module natively), and
+only two event loops that use slightly less memory (the C<Event> module
-no faster event model, not event C<Event> natively.
+natively and the pure perl backend), and no faster event models, not even
+C<Event> natively.
 The pure perl implementation is hit in a few sweet spots (both the
 zero timeout and the use of a single fd hit optimisations in the perl
-interpreter and the backend itself). Nevertheless tis shows that it
+interpreter and the backend itself, and all watchers become ready at the
-adds very little overhead in itself. Like any select-based backend its
+same time). Nevertheless this shows that it adds very little overhead in
-performance becomes really bad with lots of file descriptors, of course,
+itself. Like any select-based backend its performance becomes really bad
+with lots of file descriptors (and few of them active), of course, but
-but this was not subjetc of this benchmark.
+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, features a faster
+C<Glib>'s memory usage is quite a bit bit higher, but it features a
-callback invocation and overall lands in the same class as C<Event>.
+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
+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, though).
+hidden memory cost inside the kernel, though, that is not reflected in the
+figures above).
 C<POE>, regardless of underlying event loop (wether using its pure perl
 select-based backend or the Event module) shows abysmal performance and
 memory usage: Watchers use almost 30 times as much memory as EV watchers,
 and 10 times as much memory as both Event or EV via AnyEvent. Watcher
-invocation is almost 700 times slower than with AnyEvent's pure perl
+invocation 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.
 Using EV through AnyEvent is faster than any other event loop, but most
 event loops have acceptable performance with or without AnyEvent.
 The overhead AnyEvent adds is usually much smaller than the overhead of
 the actual event loop, only with extremely fast event loops such as the EV
-adds Anyevent significant overhead.
+adds AnyEvent significant overhead.
 And you should simply avoid POE like the plague if you want performance or
 reasonable memory usage.

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Comparing AnyEvent/lib/AnyEvent.pm (file contents): Revision 1.72 by root, Fri Apr 25 07:43:25 2008 UTC vs. Revision 1.81 by root, Fri Apr 25 13:05:17 2008 UTC

Diff Legend

Comparing AnyEvent/lib/AnyEvent.pm (file contents):
Revision 1.72 by root, Fri Apr 25 07:43:25 2008 UTC vs.
Revision 1.81 by root, Fri Apr 25 13:05:17 2008 UTC