[ViewVC] Diff of: cvs/AnyEvent/README

Comparing AnyEvent/README (file contents):
Revision 1.32 by root, Fri Oct 3 07:19:23 2008 UTC vs.
Revision 1.42 by root, Mon Jun 29 21:00:32 2009 UTC

 NAME
     AnyEvent - provide framework for multiple event loops
-    EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event
+    EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported
-    loops
+    event loops.
 SYNOPSIS
        use AnyEvent;
+       # file descriptor readable
-       my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ...  });
+       my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ...  });
+       # one-shot or repeating timers
        my $w = AnyEvent->timer (after => $seconds, cb => sub { ...  });
        my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...
        print AnyEvent->now;  # prints current event loop time
        print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
+       # POSIX signal
        my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
+       # child process exit
        my $w = AnyEvent->child (pid => $pid, cb => sub {
           my ($pid, $status) = @_;
           ...
        });
+       # called when event loop idle (if applicable)
+       my $w = AnyEvent->idle (cb => sub { ... });
        my $w = AnyEvent->condvar; # stores whether a condition was flagged
        $w->send; # wake up current and all future recv's
        $w->recv; # enters "main loop" till $condvar gets ->send
        # use a condvar in callback mode:
     These watchers are normal Perl objects with normal Perl lifetime. After
     creating a watcher it will immediately "watch" for events and invoke the
     callback when the event occurs (of course, only when the event model is
     in control).
+    Note that callbacks must not permanently change global variables
+    potentially in use by the event loop (such as $_ or $[) and that
+    callbacks must not "die". The former is good programming practise in
+    Perl and the latter stems from the fact that exception handling differs
+    widely between event loops.
     To disable the watcher you have to destroy it (e.g. by setting the
     variable you store it in to "undef" or otherwise deleting all references
     to it).
     All watchers are created by calling a method on the "AnyEvent" class.
   I/O WATCHERS
     You can create an I/O watcher by calling the "AnyEvent->io" method with
     the following mandatory key-value pairs as arguments:
-    "fh" the Perl *file handle* (*not* file descriptor) to watch for events
+    "fh" is the Perl *file handle* (*not* file descriptor) to watch for
-    (AnyEvent might or might not keep a reference to this file handle).
+    events (AnyEvent might or might not keep a reference to this file
+    handle). Note that only file handles pointing to things for which
+    non-blocking operation makes sense are allowed. This includes sockets,
+    most character devices, pipes, fifos and so on, but not for example
+    files or block devices.
     "poll" must be a string that is either "r" or "w", which creates a
-    watcher waiting for "r"eadable or "w"ritable events, respectively. "cb"
+    watcher waiting for "r"eadable or "w"ritable events, respectively.
-    is the callback to invoke each time the file handle becomes ready.
+    "cb" is the callback to invoke each time the file handle becomes ready.
     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 I/O watcher callbacks.
         In either case, if you care (and in most cases, you don't), then you
         can get whatever behaviour you want with any event loop, by taking
         the difference between "AnyEvent->time" and "AnyEvent->now" into
         account.
+    AnyEvent->now_update
+        Some event loops (such as EV or AnyEvent::Impl::Perl) cache the
+        current time for each loop iteration (see the discussion of
+        AnyEvent->now, above).
+        When a callback runs for a long time (or when the process sleeps),
+        then this "current" time will differ substantially from the real
+        time, which 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".
+        Note that updating the time *might* cause some events to be handled.
   SIGNAL WATCHERS
     You can watch for signals using a signal watcher, "signal" is the signal
     *name* in uppercase and without any "SIG" prefix, "cb" is the Perl
     callback to be invoked whenever a signal occurs.
     There is a slight catch to child watchers, however: you usually start
     them *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
+    Not all event models handle this correctly (neither POE nor IO::Async
+    do, see their AnyEvent::Impl manpages for details), but even for event
-    event models that *do* handle this correctly, they usually need to be
+    models that *do* handle this correctly, they usually need to be loaded
-    loaded before the process exits (i.e. before you fork in the first
+    before the process exits (i.e. before you fork in the first place).
-    place).
+    AnyEvent's pure perl event loop handles all cases correctly regardless
+    of when you start the watcher.
     This means you cannot create a child watcher as the very first thing in
     an AnyEvent program, you *have* to create at least one watcher before
     you "fork" the child (alternatively, you can call "AnyEvent::detect").
     Example: fork a process and wait for it
        my $done = AnyEvent->condvar;
-   my $pid = fork or exit 5;
+       my $pid = fork or exit 5;
-   my $w = AnyEvent->child (
+       my $w = AnyEvent->child (
           pid => $pid,
           cb  => sub {
              my ($pid, $status) = @_;
              warn "pid $pid exited with status $status";
              $done->send;
           },
        );
-   # do something else, then wait for process exit
+       # do something else, then wait for process exit
        $done->recv;
+  IDLE WATCHERS
+    Sometimes there is a need to do something, but it is not so important to
+    do it instantly, but only when there is nothing better to do. This
+    "nothing better to do" is usually defined to be "no other events need
+    attention by the event loop".
+    Idle watchers ideally get invoked when the event loop has nothing better
+    to do, just before it would block the process to wait for new events.
+    Instead of blocking, the idle watcher is invoked.
+    Most event loops unfortunately do not really support idle watchers (only
+    EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent
+    will simply call the callback "from time to time".
+    Example: read lines from STDIN, but only process them when the program
+    is otherwise idle:
+       my @lines; # read data
+       my $idle_w;
+       my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
+          push @lines, scalar <STDIN>;
+          # start an idle watcher, if not already done
+          $idle_w ||= AnyEvent->idle (cb => sub {
+             # handle only one line, when there are lines left
+             if (my $line = shift @lines) {
+                print "handled when idle: $line";
+             } else {
+                # otherwise disable the idle watcher again
+                undef $idle_w;
+             }
+          });
+       });
   CONDITION VARIABLES
     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.
         This can be used to signal any errors to the condition variable
         user/consumer.
     $cv->begin ([group callback])
     $cv->end
-        These two methods are EXPERIMENTAL and MIGHT CHANGE.
         These two methods can be used to combine many transactions/events
         into one. For example, a function that pings many hosts in parallel
         might want to use a condition variable for the whole process.
         Every call to "->begin" will increment a counter, and every call to
         "->end" will decrement it. If the counter reaches 0 in "->end", the
         (last) callback passed to "begin" will be executed. That callback is
         *supposed* to call "->send", but that is not required. If no
         callback was set, "send" will be called without any arguments.
-        Let's clarify this with the ping example:
+        You can think of "$cv->send" giving you an OR condition (one call
+        sends), while "$cv->begin" and "$cv->end" giving you an AND
+        condition (all "begin" calls must be "end"'ed before the condvar
+        sends).
+        Let's start with a simple example: you have two I/O watchers (for
+        example, STDOUT and STDERR for a program), and you want to wait for
+        both streams to close before activating a condvar:
+           my $cv = AnyEvent->condvar;
+           $cv->begin; # first watcher
+           my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
+              defined sysread $fh1, my $buf, 4096
+                 or $cv->end;
+           });
+           $cv->begin; # second watcher
+           my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
+              defined sysread $fh2, my $buf, 4096
+                 or $cv->end;
+           });
+           $cv->recv;
+        This works because for every event source (EOF on file handle),
+        there is one call to "begin", so the condvar waits for all calls to
+        "end" before sending.
+        The ping example mentioned above is slightly more complicated, as
+        the there are results to be passwd back, and the number of tasks
+        that are begung can potentially be zero:
            my $cv = AnyEvent->condvar;
            my %result;
            $cv->begin (sub { $cv->send (\%result) });
         the loop, which serves two important purposes: first, it sets the
         callback to be called once the counter reaches 0, and second, it
         ensures that "send" is called even when "no" hosts are being pinged
         (the loop doesn't execute once).
-        This is the general pattern when you "fan out" into multiple
+        This is the general pattern when you "fan out" into multiple (but
-        subrequests: use an outer "begin"/"end" pair to set the callback and
+        potentially none) subrequests: use an outer "begin"/"end" pair to
-        ensure "end" is called at least once, and then, for each subrequest
+        set the callback and ensure "end" is called at least once, and then,
-        you start, call "begin" and for each subrequest you finish, call
+        for each subrequest you start, call "begin" and for each subrequest
-        "end".
+        you finish, call "end".
    METHODS FOR CONSUMERS
     These methods should only be used by the consuming side, i.e. the code
     awaits the condition.
            AnyEvent::Impl::Tk        based on Tk, very bad choice.
            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.
+           # warning, support for IO::Async is only partial, as it is too broken
+           # and limited toe ven support the AnyEvent API. See AnyEvent::Impl::Async.
+           AnyEvent::Impl::IOAsync   based on IO::Async, cannot be autoprobed (see its docs).
         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
     "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
     Glib uses "install_exception_handler" and so on.
 ENVIRONMENT VARIABLES
     The following environment variables are used by this module or its
-    submodules:
+    submodules.
+    Note that AnyEvent will remove *all* environment variables starting with
+    "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
+    enabled.
     "PERL_ANYEVENT_VERBOSE"
         By default, AnyEvent will be completely silent except in fatal
         conditions. You can set this environment variable to make AnyEvent
         more talkative.
     "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 "AnyEvent::Strict" and then to
         thoroughly check the arguments passed to most method calls. If it
-        finds any problems it will croak.
+        finds any problems, it will croak.
         In other words, enables "strict" mode.
-        Unlike "use strict", it is definitely recommended ot keep it off in
+        Unlike "use strict", it is definitely recommended to keep it off in
         production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment
         while developing programs can be very useful, however.
     "PERL_ANYEVENT_MODEL"
         This can be used to specify the event model to be used by AnyEvent,
         mentioned will be used, and preference will be given to protocols
         mentioned earlier in the list.
         This variable can effectively be used for denial-of-service attacks
         against local programs (e.g. when setuid), although the impact is
-        likely small, as the program has to handle connection errors
+        likely small, as the program has to handle conenction and other
-        already-
+        failures anyways.
         Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
         IPv6, but support both and try to use both.
         "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
         resolve or contact IPv6 addresses.
     *destroy* is the time, in microseconds, that it takes to destroy a
     single watcher.
    Results
               name watchers bytes create invoke destroy comment
-             EV/EV   400000   244   0.56   0.46    0.31 EV native interface
+             EV/EV   400000   224   0.47   0.35    0.27 EV native interface
-            EV/Any   100000   244   2.50   0.46    0.29 EV + AnyEvent watchers
+            EV/Any   100000   224   2.88   0.34    0.27 EV + AnyEvent watchers
-        CoroEV/Any   100000   244   2.49   0.44    0.29 coroutines + Coro::Signal
+        CoroEV/Any   100000   224   2.85   0.35    0.28 coroutines + Coro::Signal
-          Perl/Any   100000   513   4.92   0.87    1.12 pure perl implementation
+          Perl/Any   100000   452   4.13   0.73    0.95 pure perl implementation
-       Event/Event    16000   516  31.88  31.30    0.85 Event native interface
+       Event/Event    16000   517  32.20  31.80    0.81 Event native interface
-         Event/Any    16000   590  35.75  31.42    1.08 Event + AnyEvent watchers
+         Event/Any    16000   590  35.85  31.55    1.06 Event + AnyEvent watchers
+       IOAsync/Any    16000   989  38.10  32.77   11.13 via IO::Async::Loop::IO_Poll
+       IOAsync/Any    16000   990  37.59  29.50   10.61 via IO::Async::Loop::Epoll
-          Glib/Any    16000  1357  98.22  12.41   54.00 quadratic behaviour
+          Glib/Any    16000  1357 102.33  12.31   51.00 quadratic behaviour
-            Tk/Any     2000  1860  26.97  67.98   14.00 SEGV with >> 2000 watchers
+            Tk/Any     2000  1860  27.20  66.31   14.00 SEGV with >> 2000 watchers
-         POE/Event     2000  6644 108.64 736.02   14.73 via POE::Loop::Event
+         POE/Event     2000  6328 109.99 751.67   14.02 via POE::Loop::Event
-        POE/Select     2000  6343  94.13 809.12  565.96 via POE::Loop::Select
+        POE/Select     2000  6027  94.54 809.13  579.80 via POE::Loop::Select
    Discussion
     The benchmark does *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
     few of them active), of course, but this was not subject of this
     benchmark.
     The "Event" module has a relatively high setup and callback invocation
     cost, but overall scores in on the third place.
+    "IO::Async" performs admirably well, about on par with "Event", even
+    when using its pure perl backend.
     "Glib"'s memory usage is quite a bit higher, but it features a faster
     callback invocation and overall ends up in the same class as "Event".
     However, Glib scales extremely badly, doubling the number of watchers
     increases the processing time by more than a factor of four, making it
     single "request", that is, reading the token from the pipe and
     forwarding it to another server. This includes deleting the old timeout
     and creating a new one that moves the timeout into the future.
    Results
-        name sockets create  request
+         name sockets create  request
-          EV   20000  69.01    11.16
+           EV   20000  69.01    11.16
-        Perl   20000  73.32    35.87
+         Perl   20000  73.32    35.87
+      IOAsync   20000 157.00    98.14 epoll
+      IOAsync   20000 159.31   616.06 poll
-       Event   20000 212.62   257.32
+        Event   20000 212.62   257.32
-        Glib   20000 651.16  1896.30
+         Glib   20000 651.16  1896.30
-         POE   20000 349.67 12317.24 uses POE::Loop::Event
+          POE   20000 349.67 12317.24 uses POE::Loop::Event
    Discussion
     This benchmark *does* measure scalability and overall performance of the
     particular event loop.
     EV is again fastest. Since it is using epoll on my system, the setup
     time is relatively high, though.
     Perl surprisingly comes second. It is much faster than the C-based event
     loops Event and Glib.
+    IO::Async performs very well when using its epoll backend, and still
+    quite good compared to Glib when using its pure perl backend.
     Event suffers from high setup time as well (look at its code and you
     will understand why). Callback invocation also has a high overhead
     compared to the "$_->() for .."-style loop that the Perl event loop
     uses. Event uses select or poll in basically all documented
    Summary
     *   C-based event loops perform very well with small number of watchers,
         as the management overhead dominates.
+  THE IO::Lambda BENCHMARK
+    Recently I was told about the benchmark in the IO::Lambda manpage, which
+    could be misinterpreted to make AnyEvent look bad. In fact, the
+    benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
+    better (which shouldn't come as a surprise to anybody). As such, the
+    benchmark is fine, and mostly shows that the AnyEvent backend from
+    IO::Lambda isn't very optimal. But how would AnyEvent compare when used
+    without the extra baggage? To explore this, I wrote the equivalent
+    benchmark for AnyEvent.
+    The benchmark itself creates an echo-server, and then, for 500 times,
+    connects to the echo server, sends a line, waits for the reply, and then
+    creates the next connection. This is a rather bad benchmark, as it
+    doesn't test the efficiency of the framework or much non-blocking I/O,
+    but it is a benchmark nevertheless.
+       name                    runtime
+       Lambda/select           0.330 sec
+          + optimized          0.122 sec
+       Lambda/AnyEvent         0.327 sec
+          + optimized          0.138 sec
+       Raw sockets/select      0.077 sec
+       POE/select, components  0.662 sec
+       POE/select, raw sockets 0.226 sec
+       POE/select, optimized   0.404 sec
+       AnyEvent/select/nb      0.085 sec
+       AnyEvent/EV/nb          0.068 sec
+          +state machine       0.134 sec
+    The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
+    benchmarks actually make blocking connects and use 100% blocking I/O,
+    defeating the purpose of an event-based solution. All of the newly
+    written AnyEvent benchmarks use 100% non-blocking connects (using
+    AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
+    resolver), so AnyEvent is at a disadvantage here, as non-blocking
+    connects generally require a lot more bookkeeping and event handling
+    than blocking connects (which involve a single syscall only).
+    The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
+    offers similar expressive power as POE and IO::Lambda, using
+    conventional Perl syntax. This means that both the echo server and the
+    client are 100% non-blocking, further placing it at a disadvantage.
+    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 :) AnyEvent::Handle abstraction beats both POE and IO::Lambda by a
+    large margin, even though 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 eg/ae0.pl and
+    eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
+    part of the IO::lambda distribution and were used without any changes.
 SIGNALS
     AnyEvent currently installs handlers for these signals:
     SIGCHLD
         A handler for "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 reset it to default, to avoid losing child exit statuses.
     SIGPIPE
         A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
         "undef" when AnyEvent gets loaded.
     You can make AnyEvent completely ignore this variable by deleting it
     before the first watcher gets created, e.g. with a "BEGIN" block:
        BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
-   use AnyEvent;
+       use AnyEvent;
     Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
     be used to probe what backend is used and gain other information (which
     is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
-    and $ENV{PERL_ANYEGENT_STRICT}.
+    and $ENV{PERL_ANYEVENT_STRICT}.
+    Note that AnyEvent will remove *all* environment variables starting with
+    "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
+    enabled.
 BUGS
     Perl 5.8 has numerous memleaks that sometimes hit this module and are
     hard to work around. If you suffer from memleaks, first upgrade to Perl
     5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
-    annoying mamleaks, such as leaking on "map" and "grep" but it is usually
+    annoying memleaks, such as leaking on "map" and "grep" but it is usually
     not as pronounced).
 SEE ALSO
     Utility functions: AnyEvent::Util.

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Comparing AnyEvent/README (file contents): Revision 1.32 by root, Fri Oct 3 07:19:23 2008 UTC vs. Revision 1.42 by root, Mon Jun 29 21:00:32 2009 UTC

Diff Legend

Comparing AnyEvent/README (file contents):
Revision 1.32 by root, Fri Oct 3 07:19:23 2008 UTC vs.
Revision 1.42 by root, Mon Jun 29 21:00:32 2009 UTC