[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 1.90 by root, Fri Apr 25 14:24:29 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
+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
 =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   244   2.50   0.46    0.29 EV + AnyEvent watchers
-    CoroEV/Any  100000   610   3.49   0.92    0.75 coroutines + Coro::Signal
+    CoroEV/Any   100000   244   2.49   0.44    0.29 coroutines + Coro::Signal
-      Perl/Any   16000   654   4.64   1.22    0.77 pure perl implementation
+      Perl/Any   100000   513   4.92   0.87    1.12 pure perl implementation
-   Event/Event   16000   523  28.05  21.38    0.86 Event native interface
+   Event/Event    16000   516  31.88  31.30    0.85 Event native interface
-     Event/Any   16000   943  34.43  20.48    1.39 Event + AnyEvent watchers
+     Event/Any    16000   936  39.17  33.63    1.43 Event + AnyEvent watchers
-      Glib/Any   16000  1357  96.99  12.55   55.51 quadratic behaviour
+      Glib/Any    16000  1357  98.22  12.41   54.00 quadratic behaviour
-        Tk/Any    2000  1855  27.01  66.61   14.03 SEGV with >> 2000 watchers
+        Tk/Any     2000  1860  26.97  67.98   14.00 SEGV with >> 2000 watchers
-     POE/Event    2000  6644 108.15 768.19   14.33 via POE::Loop::Event
+     POE/Event     2000  6644 108.64 736.02   14.73 via POE::Loop::Event
-    POE/Select    2000  6343  94.69 807.65  562.69 via POE::Loop::Select
+    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, 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, it uses
-only one event loop that uses less memory (the C<Event> module natively), and
+far less memory than any other event loop and is still faster than Event
-no faster event model, not event C<Event> natively.
+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
+constant 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). 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, of course,
+performance becomes really bad with lots of file descriptors (and few of
-but this was not subjetc of this benchmark.
+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,
+The C<Event> module has a relatively high setup and callback invocation
-but overall scores on the third place.
+cost, but overall scores in 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 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 which is not reflected in the figures
+above).
-C<POE>, regardless of underlying event loop (wether using its pure perl
+C<POE>, regardless of underlying event loop (whether using its pure
-select-based backend or the Event module) shows abysmal performance and
+perl select-based backend or the Event module, the POE-EV backend
+couldn't be tested because it wasn't working) shows abysmal performance
-memory usage: Watchers use almost 30 times as much memory as EV watchers,
+and memory usage: Watchers use almost 30 times as much memory as
-and 10 times as much memory as both Event or EV via AnyEvent. Watcher
+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 is almost 700 times slower than with AnyEvent's pure perl
+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
-Using EV through AnyEvent is faster than any other event loop, but most
+=item * Using EV through AnyEvent is faster than any other event loop
-event loops have acceptable performance with or without AnyEvent.
+(even when used without AnyEvent), but most event loops have acceptable
+performance with or without AnyEvent.
-The overhead AnyEvent adds is usually much smaller than the overhead of
+=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 the EV
+the actual event loop, only with extremely fast event loops such as EV
-adds Anyevent significant overhead.
+adds AnyEvent significant overhead.
-And you should simply avoid POE like the plague if you want performance or
+=item * You should 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

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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 1.90 by root, Fri Apr 25 14:24:29 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 1.90 by root, Fri Apr 25 14:24:29 2008 UTC