--- AnyEvent/README 2008/06/03 09:02:46 1.25 +++ AnyEvent/README 2009/04/20 14:34:18 1.37 @@ -7,17 +7,26 @@ SYNOPSIS use AnyEvent; - my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { - ... - }); + my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... }); + + 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. + + my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... }); - my $w = AnyEvent->timer (after => $seconds, cb => sub { + my $w = AnyEvent->child (pid => $pid, cb => sub { + my ($pid, $status) = @_; ... }); 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 @@ -32,11 +41,12 @@ policy* and AnyEvent is *small and efficient*. First and foremost, *AnyEvent is not an event model* itself, it only - interfaces to whatever event model the main program happens to use in a + interfaces to whatever event model the main program happens to use, in a pragmatic way. For event models and certain classes of immortals alike, the statement "there can only be one" is a bitter reality: In general, only one event loop can be active at the same time in a process. - AnyEvent helps hiding the differences between those event loops. + AnyEvent cannot change this, but it can hide the differences between + those event loops. The goal of AnyEvent is to offer module authors the ability to do event programming (waiting for I/O or timer events) without subscribing to a @@ -47,8 +57,8 @@ For modules like POE or IO::Async (which is a total misnomer as it is actually doing all I/O *synchronously*...), using them in your module is like joining a cult: After you joined, you are dependent on them and you - cannot use anything else, as it is simply incompatible to everything - that isn't itself. What's worse, all the potential users of your module + cannot use anything else, as they are simply incompatible to everything + that isn't them. What's worse, all the potential users of your module are *also* forced to use the same event loop you use. AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works @@ -56,9 +66,9 @@ with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your module uses one of those, every user of your module has to use it, too. But if your module uses AnyEvent, it works transparently with all event - models it supports (including stuff like POE and IO::Async, as long as - those use one of the supported event loops. It is trivial to add new - event loops to AnyEvent, too, so it is future-proof). + models it supports (including stuff like IO::Async, as long as those use + one of the supported event loops. It is trivial to add new event loops + to AnyEvent, too, so it is future-proof). In addition to being free of having to use *the one and only true event model*, AnyEvent also is free of bloat and policy: with POE or similar @@ -124,6 +134,12 @@ 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). @@ -148,10 +164,17 @@ 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. + "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 @@ -165,9 +188,9 @@ always use non-blocking calls when reading/writing from/to your file handles. - Example: + Example: wait for readability of STDIN, then read a line and disable the + watcher. - # wait for readability of STDIN, then read a line and disable the watcher my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { chomp (my $input = ); warn "read: $input\n"; @@ -186,13 +209,18 @@ 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). + The callback will normally be invoked once only. If you specify another + parameter, "interval", as a strictly positive number (> 0), then the + callback will be invoked regularly at that interval (in fractional + seconds) after the first invocation. If "interval" is specified with a + false value, then it is treated as if it were missing. + + The callback will be rescheduled before invoking the callback, but no + attempt is done to avoid timer drift in most backends, so the interval + is only approximate. - Example: + Example: fire an event after 7.7 seconds. - # fire an event after 7.7 seconds my $w = AnyEvent->timer (after => 7.7, cb => sub { warn "timeout\n"; }); @@ -200,19 +228,12 @@ # to cancel the timer: undef $w; - Example 2: - - # fire an event after 0.5 seconds, then roughly every second - my $w; + Example 2: fire an event after 0.5 seconds, then roughly every second. - my $cb = sub { - # cancel the old timer while creating a new one - $w = AnyEvent->timer (after => 1, cb => $cb); + my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub { + warn "timeout\n"; }; - # start the "loop" by creating the first watcher - $w = AnyEvent->timer (after => 0.5, cb => $cb); - TIMING ISSUES There are two ways to handle timers: based on real time (relative, "fire in 10 seconds") and based on wallclock time (absolute, "fire at 12 @@ -295,10 +316,24 @@ 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* without any "SIG" prefix, "cb" is the Perl callback to be invoked - whenever a signal occurs. + *name* in uppercase and without any "SIG" prefix, "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 @@ -323,11 +358,18 @@ 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 @@ -373,8 +415,10 @@ 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 +484,23 @@ 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 +630,7 @@ 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. @@ -700,27 +761,53 @@ blocking functions such as "inet_aton" by event-/callback-based versions. - AnyEvent::Handle - Provide read and write buffers and manages watchers for reads and - writes. - AnyEvent::Socket Provides various utility functions for (internet protocol) sockets, addresses and name resolution. Also functions to create non-blocking tcp connections or tcp servers, with IPv6 and SRV record support and more. + AnyEvent::Handle + Provide read and write buffers, manages watchers for reads and + writes, supports raw and formatted I/O, I/O queued and fully + transparent and non-blocking SSL/TLS. + AnyEvent::DNS Provides rich asynchronous DNS resolver capabilities. + AnyEvent::HTTP + A simple-to-use HTTP library that is capable of making a lot of + concurrent HTTP requests. + AnyEvent::HTTPD Provides a simple web application server framework. AnyEvent::FastPing The fastest ping in the west. - Net::IRC3 - AnyEvent based IRC client module family. + AnyEvent::DBI + Executes DBI requests asynchronously in a proxy process. + + AnyEvent::AIO + Truly asynchronous I/O, should be in the toolbox of every event + programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent + together. + + AnyEvent::BDB + Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently + fuses BDB and AnyEvent together. + + AnyEvent::GPSD + A non-blocking interface to gpsd, a daemon delivering GPS + information. + + AnyEvent::IGS + A non-blocking interface to the Internet Go Server protocol (used by + App::IGS). + + AnyEvent::IRC + AnyEvent based IRC client module family (replacing the older + Net::IRC3). Net::XMPP2 AnyEvent based XMPP (Jabber protocol) module family. @@ -735,64 +822,29 @@ Coro Has special support for AnyEvent via Coro::AnyEvent. - AnyEvent::AIO, IO::AIO - Truly asynchronous I/O, should be in the toolbox of every event - programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent - together. - - AnyEvent::BDB, BDB - Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently - fuses IO::AIO and AnyEvent together. - IO::Lambda 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: "PERL_ANYEVENT_VERBOSE" By default, AnyEvent will be completely silent except in fatal @@ -806,6 +858,19 @@ When set to 2 or higher, cause AnyEvent to report to STDERR which event model it chooses. + "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. + + In other words, enables "strict" mode. + + Unlike "use strict", it is definitely recommended ot 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, before auto detection and -probing kicks in. It must be a string @@ -833,8 +898,8 @@ 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. @@ -856,6 +921,49 @@ 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 @@ -1051,16 +1159,16 @@ 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 + 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 @@ -1251,6 +1359,30 @@ * C-based event loops perform very well with small number of watchers, as the management overhead dominates. +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. + + 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. @@ -1276,7 +1408,15 @@ 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). + is probably even less useful to an attacker than PERL_ANYEVENT_MODEL), + and $ENV{PERL_ANYEGENT_STRICT}. + +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 memleaks, such as leaking on "map" and "grep" but it is usually + not as pronounced). SEE ALSO Utility functions: AnyEvent::Util.