--- AnyEvent/README 2009/07/17 14:57:03 1.45 +++ AnyEvent/README 2010/01/05 10:45:25 1.59 @@ -1,8 +1,8 @@ NAME - AnyEvent - provide framework for multiple event loops + AnyEvent - the DBI of event loop programming - EV, Event, Glib, Tk, Perl, Event::Lib, Qt and POE are various supported - event loops. + EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async, + Qt and POE are various supported event loops/environments. SYNOPSIS use AnyEvent; @@ -40,6 +40,13 @@ tutorial or some gentle introduction, have a look at the AnyEvent::Intro manpage. +SUPPORT + There is a mailinglist for discussing all things AnyEvent, and an IRC + channel, too. + + See the AnyEvent project page at the Schmorpforge Ta-Sa Software + Repository, at , for more info. + WHY YOU SHOULD USE THIS MODULE (OR NOT) Glib, POE, IO::Async, Event... CPAN offers event models by the dozen nowadays. So what is different about AnyEvent? @@ -168,6 +175,12 @@ declared. I/O WATCHERS + $w = AnyEvent->io ( + fh => , + poll => <"r" or "w">, + cb => , + ); + You can create an I/O watcher by calling the "AnyEvent->io" method with the following mandatory key-value pairs as arguments: @@ -205,6 +218,14 @@ }); TIME WATCHERS + $w = AnyEvent->timer (after => , cb => ); + + $w = AnyEvent->timer ( + after => , + interval => , + cb => , + ); + You can create a time watcher by calling the "AnyEvent->timer" method with the following mandatory arguments: @@ -335,9 +356,19 @@ When this is the case, you can call this method, which will update the event loop's idea of "current time". + A typical example would be a script in a web server (e.g. + "mod_perl") - when mod_perl executes the script, then the event loop + will have the wrong idea about the "current time" (being potentially + far in the past, when the script ran the last time). In that case + you should arrange a call to "AnyEvent->now_update" each time the + web server process wakes up again (e.g. at the start of your script, + or in a handler). + Note that updating the time *might* cause some events to be handled. SIGNAL WATCHERS + $w = AnyEvent->signal (signal => , cb => ); + 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. @@ -352,22 +383,61 @@ process, but it is guaranteed not to interrupt any other callbacks. The main advantage of using these watchers is that you can share a - signal between multiple watchers. + signal between multiple watchers, and AnyEvent will ensure that signals + will not interrupt your program at bad times. - This watcher might use %SIG, so programs overwriting those signals - directly will likely not work correctly. + This watcher might use %SIG (depending on the event loop used), so + programs overwriting those signals directly will likely not work + correctly. Example: exit on SIGINT my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); + Restart Behaviour + While restart behaviour is up to the event loop implementation, most + will not restart syscalls (that includes Async::Interrupt and AnyEvent's + pure perl implementation). + + Safe/Unsafe Signals + Perl signals can be either "safe" (synchronous to opcode handling) or + "unsafe" (asynchronous) - the former might get delayed indefinitely, the + latter might corrupt your memory. + + AnyEvent signal handlers are, in addition, synchronous to the event + loop, i.e. they will not interrupt your running perl program but will + only be called as part of the normal event handling (just like timer, + I/O etc. callbacks, too). + + Signal Races, Delays and Workarounds + Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching + callbacks to signals in a generic way, which is a pity, as you cannot do + race-free signal handling in perl, requiring C libraries for this. + AnyEvent will try to do it's best, which means in some cases, signals + will be delayed. The maximum time a signal might be delayed is specified + in $AnyEvent::MAX_SIGNAL_LATENCY (default: 10 seconds). This variable + can be changed only before the first signal watcher is created, and + should be left alone otherwise. This variable determines how often + AnyEvent polls for signals (in case a wake-up was missed). Higher values + will cause fewer spurious wake-ups, which is better for power and CPU + saving. + + All these problems can be avoided by installing the optional + Async::Interrupt module, which works with most event loops. It will not + work with inherently broken event loops such as Event or Event::Lib (and + not with POE currently, as POE does it's own workaround with one-second + latency). For those, you just have to suffer the delays. + CHILD PROCESS WATCHERS + $w = AnyEvent->child (pid => , cb => ); + 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 triggered only - when the child process has finished and an exit status is available, not - on any trace events (stopped/continued). + The child process is specified by the "pid" argument (one some backends, + using 0 watches for any child process exit, on others this will croak). + The watcher will be 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 @@ -393,6 +463,10 @@ an AnyEvent program, you *have* to create at least one watcher before you "fork" the child (alternatively, you can call "AnyEvent::detect"). + As most event loops do not support waiting for child events, they will + be emulated by AnyEvent in most cases, in which the latency and race + problems mentioned in the description of signal watchers apply. + Example: fork a process and wait for it my $done = AnyEvent->condvar; @@ -412,18 +486,23 @@ $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". + $w = AnyEvent->idle (cb => ); + + Repeatedly invoke the callback after the process becomes idle, until + either the watcher is destroyed or new events have been detected. + + Idle watchers are useful when there is a need to do something, but it is + not so important (or wise) to do it instantly. The callback will be + invoked only when there is "nothing better to do", which is usually + defined as "all outstanding events have been handled and no new events + have been detected". That means that idle watchers ideally get invoked + when the event loop has just polled for new events but none have been + detected. Instead of blocking to wait for more events, the idle watchers + will be invoked. + + Unfortunately, most event loops 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: @@ -446,6 +525,11 @@ }); CONDITION VARIABLES + $cv = AnyEvent->condvar; + + $cv->send (); + my @res = $cv->recv; + 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. @@ -475,7 +559,8 @@ in time where multiple outstanding events have been processed. And yet another way to call them is transactions - each condition variable can be used to represent a transaction, which finishes at some point and - delivers a result. + delivers a result. And yet some people know them as "futures" - a + promise to compute/deliver something that you can wait for. Condition variables are very useful to signal that something has finished, for example, if you write a module that does asynchronous http @@ -519,7 +604,7 @@ ); # this "blocks" (while handling events) till the callback - # calls -send $result_ready->recv; Example: wait for a timer, but take advantage of the fact that condition @@ -586,9 +671,10 @@ Every call to "->begin" will increment a counter, and every call to "->end" will decrement it. If the counter reaches 0 in "->end", the - (last) callback passed to "begin" will be executed. That callback is - *supposed* to call "->send", but that is not required. If no - callback was set, "send" will be called without any arguments. + (last) callback passed to "begin" will be executed, passing the + condvar as first argument. That callback is *supposed* to call + "->send", but that is not required. If no group callback was set, + "send" will be called without any arguments. You can think of "$cv->send" giving you an OR condition (one call sends), while "$cv->begin" and "$cv->end" giving you an AND @@ -626,7 +712,7 @@ my $cv = AnyEvent->condvar; my %result; - $cv->begin (sub { $cv->send (\%result) }); + $cv->begin (sub { shift->send (\%result) }); for my $host (@list_of_hosts) { $cv->begin; @@ -703,22 +789,22 @@ This is a mutator function that returns the callback set and optionally replaces it before doing so. - The callback will be called when the condition becomes "true", i.e. - when "send" or "croak" are called, with the only argument being the - condition variable itself. Calling "recv" inside the callback or at - any later time is guaranteed not to block. + The callback will be called when the condition becomes (or already + was) "true", i.e. when "send" or "croak" are called (or were + called), with the only argument being the condition variable itself. + Calling "recv" inside the callback or at any later time is + guaranteed not to block. SUPPORTED EVENT LOOPS/BACKENDS The available backend classes are (every class has its own manpage): Backends that are autoprobed when no other event loop can be found. EV is the preferred backend when no other event loop seems to be in - use. If EV is not installed, then AnyEvent will try Event, and, - failing that, will fall back to its own pure-perl implementation, - which is available everywhere as it comes with AnyEvent itself. + use. If EV is not installed, then AnyEvent will fall back to its own + pure-perl implementation, which is available everywhere as it comes + with AnyEvent itself. AnyEvent::Impl::EV based on EV (interface to libev, best choice). - AnyEvent::Impl::Event based on Event, very stable, few glitches. AnyEvent::Impl::Perl pure-perl implementation, fast and portable. Backends that are transparently being picked up when they are used. @@ -729,10 +815,12 @@ anything starts to create watchers. Nothing special needs to be done by the main program. + AnyEvent::Impl::Event based on Event, very stable, few glitches. AnyEvent::Impl::Glib based on Glib, slow but very stable. AnyEvent::Impl::Tk based on Tk, very broken. AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. AnyEvent::Impl::POE based on POE, very slow, some limitations. + AnyEvent::Impl::Irssi used when running within irssi. Backends with special needs. Qt requires the Qt::Application to be instantiated first, but will @@ -807,7 +895,24 @@ If called in scalar or list context, then it creates and returns an object that automatically removes the callback again when it is - destroyed. See Coro::BDB for a case where this is useful. + destroyed (or "undef" when the hook was immediately executed). See + AnyEvent::AIO for a case where this is useful. + + Example: Create a watcher for the IO::AIO module and store it in + $WATCHER. Only do so after the event loop is initialised, though. + + our WATCHER; + + my $guard = AnyEvent::post_detect { + $WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb); + }; + + # the ||= is important in case post_detect immediately runs the block, + # as to not clobber the newly-created watcher. assigning both watcher and + # post_detect guard to the same variable has the advantage of users being + # able to just C if the watcher causes them grief. + + $WATCHER ||= $guard; @AnyEvent::post_detect If there are any code references in this array (you can "push" to it @@ -819,7 +924,7 @@ detected, and the array will be ignored. Best use "AnyEvent::post_detect { BLOCK }" when your application - allows it,as it takes care of these details. + allows it, as it takes care of these details. This variable is mainly useful for modules that can do something useful when AnyEvent is used and thus want to know when it is @@ -827,6 +932,19 @@ provides the means to hook into AnyEvent passively, without loading it. + Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used + together, you could put this into Coro (this is the actual code used + by Coro to accomplish this): + + if (defined $AnyEvent::MODEL) { + # AnyEvent already initialised, so load Coro::AnyEvent + require Coro::AnyEvent; + } else { + # AnyEvent not yet initialised, so make sure to load Coro::AnyEvent + # as soon as it is + push @AnyEvent::post_detect, sub { require Coro::AnyEvent }; + } + WHAT TO DO IN A MODULE As a module author, you should "use AnyEvent" and call AnyEvent methods freely, but you should not load a specific event module or rely on it. @@ -957,6 +1075,13 @@ Coro Has special support for AnyEvent via Coro::AnyEvent. +SIMPLIFIED AE API + Starting with version 5.0, AnyEvent officially supports a second, much + simpler, API that is designed to reduce the calling, typing and memory + overhead. + + See the AE manpage for details. + 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 @@ -993,6 +1118,10 @@ When set to 2 or higher, cause AnyEvent to report to STDERR which event model it chooses. + When set to 8 or higher, then AnyEvent will report extra information + on which optional modules it loads and how it implements certain + features. + "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 @@ -1002,9 +1131,10 @@ In other words, enables "strict" mode. - 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. + Unlike "use strict" (or it's modern cousin, "use common::sense", 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, @@ -1072,6 +1202,10 @@ variables exist, they will be used to specify CA certificate locations instead of a system-dependent default. + "PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT" + When these are set to 1, then the respective modules are not loaded. + Mostly good for testing AnyEvent itself. + 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 @@ -1135,16 +1269,9 @@ }, ); - my $time_watcher; # can only be used once - - sub new_timer { - $timer = AnyEvent->timer (after => 1, cb => sub { - warn "timeout\n"; # print 'timeout' about every second - &new_timer; # and restart the time - }); - } - - new_timer; # create first timer + my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub { + warn "timeout\n"; # print 'timeout' at most every second + }); $cv->recv; # wait until user enters /^q/i @@ -1281,7 +1408,8 @@ which it is), lets them fire exactly once and destroys them again. Source code for this benchmark is found as eg/bench in the AnyEvent - distribution. + distribution. It uses the AE interface, which makes a real difference + for the EV and Perl backends only. Explanation of the columns *watcher* is the number of event watchers created/destroyed. Since @@ -1310,18 +1438,18 @@ Results name watchers bytes create invoke destroy comment - 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 + EV/EV 100000 223 0.47 0.43 0.27 EV native interface + EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers + Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal + Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation + Event/Event 16000 516 31.16 31.84 0.82 Event native interface + Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers + IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll + IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll + Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour + Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers + POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event + POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select Discussion The benchmark does *not* measure scalability of the event loop very @@ -1342,9 +1470,10 @@ CPU cycles with POE. "EV" is the sole leader regarding speed and memory use, which are both - maximal/minimal, respectively. Even when going through AnyEvent, it uses - far less memory than any other event loop and is still faster than Event - natively. + maximal/minimal, respectively. When using the AE API there is zero + overhead (when going through the AnyEvent API create is about 5-6 times + slower, with other times being equal, so still uses far less memory than + any other event loop and is still faster than Event natively). The pure perl implementation is hit in a few sweet spots (both the constant timeout and the use of a single fd hit optimisations in the @@ -1424,7 +1553,8 @@ many connections, most of which are idle at any one point in time. Source code for this benchmark is found as eg/bench2 in the AnyEvent - distribution. + distribution. It uses the AE interface, which makes a real difference + for the EV and Perl backends only. Explanation of the columns *sockets* is the number of sockets, and twice the number of "servers" @@ -1440,13 +1570,13 @@ Results 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 + EV 20000 62.66 7.99 + Perl 20000 68.32 32.64 + IOAsync 20000 174.06 101.15 epoll + IOAsync 20000 174.67 610.84 poll + Event 20000 202.69 242.91 + Glib 20000 557.01 1689.52 + POE 20000 341.54 12086.32 uses POE::Loop::Event Discussion This benchmark *does* measure scalability and overall performance of the @@ -1569,13 +1699,13 @@ 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. + slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda + higher level ("unoptimised") abstractions 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. + part of the IO::Lambda distribution and were used without any changes. SIGNALS AnyEvent currently installs handlers for these signals: @@ -1605,13 +1735,100 @@ Feel free to install your own handler, or reset it to defaults. +RECOMMENDED/OPTIONAL MODULES + One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and + it's built-in modules) are required to use it. + + That does not mean that AnyEvent won't take advantage of some additional + modules if they are installed. + + This section explains which additional modules will be used, and how + they affect AnyEvent's operation. + + Async::Interrupt + This slightly arcane module is used to implement fast signal + handling: To my knowledge, there is no way to do completely + race-free and quick signal handling in pure perl. To ensure that + signals still get delivered, AnyEvent will start an interval timer + to wake up perl (and catch the signals) with some delay (default is + 10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY). + + If this module is available, then it will be used to implement + signal catching, which means that signals will not be delayed, and + the event loop will not be interrupted regularly, which is more + efficient (and good for battery life on laptops). + + This affects not just the pure-perl event loop, but also other event + loops that have no signal handling on their own (e.g. Glib, Tk, Qt). + + Some event loops (POE, Event, Event::Lib) offer signal watchers + natively, and either employ their own workarounds (POE) or use + AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY). + Installing Async::Interrupt does nothing for those backends. + + EV This module isn't really "optional", as it is simply one of the + backend event loops that AnyEvent can use. However, it is simply the + best event loop available in terms of features, speed and stability: + It supports the AnyEvent API optimally, implements all the watcher + types in XS, does automatic timer adjustments even when no monotonic + clock is available, can take avdantage of advanced kernel interfaces + such as "epoll" and "kqueue", and is the fastest backend *by far*. + You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and + Glib::EV). + + Guard + The guard module, when used, will be used to implement + "AnyEvent::Util::guard". This speeds up guards considerably (and + uses a lot less memory), but otherwise doesn't affect guard + operation much. It is purely used for performance. + + JSON and JSON::XS + One of these modules is required when you want to read or write JSON + data via AnyEvent::Handle. It is also written in pure-perl, but can + take advantage of the ultra-high-speed JSON::XS module when it is + installed. + + In fact, AnyEvent::Handle will use JSON::XS by default if it is + installed. + + Net::SSLeay + Implementing TLS/SSL in Perl is certainly interesting, but not very + worthwhile: If this module is installed, then AnyEvent::Handle (with + the help of AnyEvent::TLS), gains the ability to do TLS/SSL. + + Time::HiRes + This module is part of perl since release 5.008. It will be used + when the chosen event library does not come with a timing source on + it's own. The pure-perl event loop (AnyEvent::Impl::Perl) will + additionally use it to try to use a monotonic clock for timing + stability. + 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. - Only EV is fully fork-aware. + because they rely on inefficient but fork-safe "select" or "poll" calls + - higher performance APIs such as BSD's kqueue or the dreaded Linux + epoll are usually badly thought-out hacks that are incompatible with + fork in one way or another. Only EV is fully fork-aware and ensures that + you continue event-processing in both parent and child (or both, if you + know what you are doing). + + This means that, in general, you cannot fork and do event processing in + the child if the event library was initialised before the fork (which + usually happens when the first AnyEvent watcher is created, or the + library is loaded). If you have to fork, you must either do so *before* creating your first - watcher OR you must not use AnyEvent at all in the child. + watcher OR you must not use AnyEvent at all in the child OR you must do + something completely out of the scope of AnyEvent. + + The problem of doing event processing in the parent *and* the child is + much more complicated: even for backends that *are* fork-aware or + fork-safe, their behaviour is not usually what you want: fork clones all + watchers, that means all timers, I/O watchers etc. are active in both + parent and child, which is almost never what you want. USing "exec" to + start worker children from some kind of manage rprocess is usually + preferred, because it is much easier and cleaner, at the expense of + having to have another binary. SECURITY CONSIDERATIONS AnyEvent can be forced to load any event model via @@ -1653,7 +1870,7 @@ Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE, - AnyEvent::Impl::IOAsync. + AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi. Non-blocking file handles, sockets, TCP clients and servers: AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.