--- AnyEvent/README 2008/07/12 20:45:27 1.28 +++ AnyEvent/README 2009/06/26 06:33:17 1.41 @@ -1,23 +1,39 @@ NAME AnyEvent - provide framework for multiple event loops - EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event - loops + EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported + event loops. SYNOPSIS use AnyEvent; - my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { - ... - }); + # file descriptor readable + my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... }); - my $w = AnyEvent->timer (after => $seconds, 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: + $w->cb (sub { $_[0]->recv }); INTRODUCTION/TUTORIAL This manpage is mainly a reference manual. If you are interested in a @@ -125,6 +141,12 @@ 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). @@ -149,11 +171,17 @@ 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 - (AnyEvent might or might not keep a reference to this file handle). + "fh" is the Perl *file handle* (*not* file descriptor) to watch for + 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" - is the callback to invoke each time the file handle becomes ready. + watcher waiting for "r"eadable or "w"ritable events, respectively. + + "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 @@ -295,6 +323,20 @@ 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 @@ -323,20 +365,29 @@ You can also watch on a child process exit and catch its exit status. The child process is specified by the "pid" argument (if set to 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 "SIGCHLD". The callback will be called with the pid - and exit status (as returned by waitpid), so unlike other watcher types, - you *can* rely on child watcher callback arguments. + watches for any child process exit). The watcher will triggered only + when the child process has finished and an exit status is available, not + on any trace events (stopped/continued). + + The callback will be called with the pid and exit status (as returned by + waitpid), so unlike other watcher types, you *can* rely on child watcher + callback arguments. + + This watcher type works by installing a signal handler for "SIGCHLD", + and since it cannot be shared, nothing else should use SIGCHLD or reap + random child processes (waiting for specific child processes, e.g. + inside "system", is just fine). 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 - event models that *do* handle this correctly, they usually need to be - loaded before the process exits (i.e. before you fork in the first - place). + Not all event models handle this correctly (neither POE nor IO::Async + do, see their AnyEvent::Impl manpages for details), but even for event + models that *do* handle this correctly, they usually need to be loaded + before the process exits (i.e. before you fork in the first 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 @@ -345,10 +396,10 @@ Example: fork a process and wait for it my $done = AnyEvent->condvar; - - my $pid = fork or exit 5; - - my $w = AnyEvent->child ( + + my $pid = fork or exit 5; + + my $w = AnyEvent->child ( pid => $pid, cb => sub { my ($pid, $status) = @_; @@ -356,10 +407,44 @@ $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 ; + + # 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 @@ -373,8 +458,10 @@ Condition variables can be created by calling the "AnyEvent->condvar" method, usually without arguments. The only argument pair allowed is + "cb", which specifies a callback to be called when the condition - variable becomes true. + 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" by calling the "send" method (or calling the condition variable @@ -440,6 +527,23 @@ my $delay = AnyEvent->timer (after => 5, cb => $done); $done->recv; + Example: Imagine an API that returns a condvar and doesn't support + callbacks. This is how you make a synchronous call, for example from the + main program: + + use AnyEvent::CouchDB; + + ... + + my @info = $couchdb->info->recv; + + And this is how you would just ste a callback to be called whenever the + results are available: + + $couchdb->info->cb (sub { + my @info = $_[0]->recv; + }); + METHODS FOR PRODUCERS These methods should only be used by the producing side, i.e. the code/module that eventually sends the signal. Note that it is also the @@ -569,7 +673,7 @@ Returns true when the condition is "true", i.e. whether "send" or "croak" have been called. - $cb = $cv->cb ([new callback]) + $cb = $cv->cb ($cb->($cv)) This is a mutator function that returns the callback set and optionally replaces it before doing so. @@ -597,6 +701,10 @@ 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 @@ -744,8 +852,9 @@ A non-blocking interface to the Internet Go Server protocol (used by App::IGS). - Net::IRC3 - AnyEvent based IRC client module family. + AnyEvent::IRC + AnyEvent based IRC client module family (replacing the older + Net::IRC3). Net::XMPP2 AnyEvent based XMPP (Jabber protocol) module family. @@ -764,51 +873,29 @@ The lambda approach to I/O - don't ask, look there. Can use AnyEvent. -SUPPLYING YOUR OWN EVENT MODEL INTERFACE - This is an advanced topic that you do not normally need to use AnyEvent - in a module. This section is only of use to event loop authors who want - to provide AnyEvent compatibility. - - If you need to support another event library which isn't directly - supported by AnyEvent, you can supply your own interface to it by - pushing, before the first watcher gets created, the package name of the - event module and the package name of the interface to use onto - @AnyEvent::REGISTRY. You can do that before and even without loading - AnyEvent, so it is reasonably cheap. - - Example: - - push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; - - This tells AnyEvent to (literally) use the "urxvt::anyevent::" - package/class when it finds the "urxvt" package/module is already - loaded. - - When AnyEvent is loaded and asked to find a suitable event model, it - will first check for the presence of urxvt by trying to "use" the - "urxvt::anyevent" module. - - The class should provide implementations for all watcher types. See - AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and - so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see - the sources. - - If you don't provide "signal" and "child" watchers than AnyEvent will - provide suitable (hopefully) replacements. - - The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) - terminal emulator uses the above line as-is. An interface isn't included - in AnyEvent because it doesn't make sense outside the embedded - interpreter inside *rxvt-unicode*, and it is updated and maintained as - part of the *rxvt-unicode* distribution. - - *rxvt-unicode* also cheats a bit by not providing blocking access to - condition variables: code blocking while waiting for a condition will - "die". This still works with most modules/usages, and blocking calls - must not be done in an interactive application, so it makes sense. +ERROR AND EXCEPTION HANDLING + In general, AnyEvent does not do any error handling - it relies on the + caller to do that if required. The AnyEvent::Strict module (see also the + "PERL_ANYEVENT_STRICT" environment variable, below) provides strict + checking of all AnyEvent methods, however, which is highly useful during + development. + + As for exception handling (i.e. runtime errors and exceptions thrown + while executing a callback), this is not only highly event-loop + specific, but also not in any way wrapped by this module, as this is the + job of the main program. + + The pure perl event loop simply re-throws the exception (usually within + "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: + The following environment variables are used by this module or its + 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 @@ -827,12 +914,13 @@ 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 - production. + 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, @@ -861,8 +949,8 @@ 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 - already- + likely small, as the program has to handle conenction and other + failures anyways. Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over IPv6, but support both and try to use both. @@ -884,6 +972,49 @@ The maximum number of child processes that "AnyEvent::Util::fork_call" will create in parallel. +SUPPLYING YOUR OWN EVENT MODEL INTERFACE + This is an advanced topic that you do not normally need to use AnyEvent + in a module. This section is only of use to event loop authors who want + to provide AnyEvent compatibility. + + If you need to support another event library which isn't directly + supported by AnyEvent, you can supply your own interface to it by + pushing, before the first watcher gets created, the package name of the + event module and the package name of the interface to use onto + @AnyEvent::REGISTRY. You can do that before and even without loading + AnyEvent, so it is reasonably cheap. + + Example: + + push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; + + This tells AnyEvent to (literally) use the "urxvt::anyevent::" + package/class when it finds the "urxvt" package/module is already + loaded. + + When AnyEvent is loaded and asked to find a suitable event model, it + will first check for the presence of urxvt by trying to "use" the + "urxvt::anyevent" module. + + The class should provide implementations for all watcher types. See + AnyEvent::Impl::EV (source code), AnyEvent::Impl::Glib (Source code) and + so on for actual examples. Use "perldoc -m AnyEvent::Impl::Glib" to see + the sources. + + If you don't provide "signal" and "child" watchers than AnyEvent will + provide suitable (hopefully) replacements. + + The above example isn't fictitious, the *rxvt-unicode* (a.k.a. urxvt) + terminal emulator uses the above line as-is. An interface isn't included + in AnyEvent because it doesn't make sense outside the embedded + interpreter inside *rxvt-unicode*, and it is updated and maintained as + part of the *rxvt-unicode* distribution. + + *rxvt-unicode* also cheats a bit by not providing blocking access to + condition variables: code blocking while waiting for a condition will + "die". This still works with most modules/usages, and blocking calls + must not be done in an interactive application, so it makes sense. + EXAMPLE PROGRAM 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 @@ -1079,16 +1210,18 @@ 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 590 35.75 31.42 1.08 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 + EV/EV 400000 224 0.47 0.35 0.27 EV native interface + EV/Any 100000 224 2.88 0.34 0.27 EV + AnyEvent watchers + CoroEV/Any 100000 224 2.85 0.35 0.28 coroutines + Coro::Signal + Perl/Any 100000 452 4.13 0.73 0.95 pure perl implementation + Event/Event 16000 517 32.20 31.80 0.81 Event native interface + 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 102.33 12.31 51.00 quadratic behaviour + Tk/Any 2000 1860 27.20 66.31 14.00 SEGV with >> 2000 watchers + POE/Event 2000 6328 109.99 751.67 14.02 via POE::Loop::Event + 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 @@ -1124,6 +1257,9 @@ 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 @@ -1203,12 +1339,14 @@ and creating a new one that moves the timeout into the future. Results - name sockets create request - EV 20000 69.01 11.16 - Perl 20000 73.32 35.87 - Event 20000 212.62 257.32 - Glib 20000 651.16 1896.30 - POE 20000 349.67 12317.24 uses POE::Loop::Event + name sockets create request + EV 20000 69.01 11.16 + 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 + Glib 20000 651.16 1896.30 + POE 20000 349.67 12317.24 uses POE::Loop::Event Discussion This benchmark *does* measure scalability and overall performance of the @@ -1220,6 +1358,9 @@ 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 @@ -1279,6 +1420,90 @@ * 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. + + The rationale for this is that AnyEvent users usually do not really + depend on SIGPIPE delivery (which is purely an optimisation for + shell use, or badly-written programs), but "SIGPIPE" can cause + spurious and rare program exits as a lot of people do not expect + "SIGPIPE" when writing to some random socket. + + The rationale for installing a no-op handler as opposed to ignoring + it is that this way, the handler will be restored to defaults on + exec. + + Feel free to install your own handler, or reset it to defaults. + FORK Most event libraries are not fork-safe. The ones who are usually are because they rely on inefficient but fork-safe "select" or "poll" calls. @@ -1299,19 +1524,23 @@ 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