--- AnyEvent/README 2008/07/29 10:20:33 1.29 +++ AnyEvent/README 2009/07/28 11:02:19 1.49 @@ -1,27 +1,34 @@ NAME - AnyEvent - provide framework for multiple event loops + AnyEvent - the DBI of event loop programming - EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - 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; - my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... }); + # file descriptor readable + 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 @@ -33,6 +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? @@ -134,6 +148,12 @@ 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). @@ -158,11 +178,17 @@ 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* (or a naked 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 @@ -304,6 +330,20 @@ 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 @@ -319,45 +359,76 @@ 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 }); + 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. AnyEvent will try to do it's best, + but 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. 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. This 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). With those, you just + have to suffer the delays. + CHILD PROCESS WATCHERS 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. + 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 + 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 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; - - 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) = @_; @@ -365,24 +436,60 @@ $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 will actively watch for new events and call your callbacks. - AnyEvent is different, it expects somebody else to run the event loop - and will only block when necessary (usually when told by the user). + AnyEvent is slightly different: it expects somebody else to run the + event loop and will only block when necessary (usually when told by the + user). The instrument to do that is called a "condition variable", so called because they represent a condition that must become true. + Now is probably a good time to look at the examples further below. + 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, with the condition variable as the first argument (but not the results). @@ -397,7 +504,8 @@ 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 @@ -441,11 +549,11 @@ ); # this "blocks" (while handling events) till the callback - # calls send + # calls -recv; Example: wait for a timer, but take advantage of the fact that condition - variables are also code references. + variables are also callable directly. my $done = AnyEvent->condvar; my $delay = AnyEvent->timer (after => 5, cb => $done); @@ -461,7 +569,7 @@ my @info = $couchdb->info->recv; - And this is how you would just ste a callback to be called whenever the + And this is how you would just set a callback to be called whenever the results are available: $couchdb->info->cb (sub { @@ -486,25 +594,22 @@ future "->recv" calls. Condition variables are overloaded so one can call them directly (as - a code reference). Calling them directly is the same as calling - "send". Note, however, that many C-based event loops do not handle - overloading, so as tempting as it may be, passing a condition - variable instead of a callback does not work. Both the pure perl and - EV loops support overloading, however, as well as all functions that - use perl to invoke a callback (as in AnyEvent::Socket and - AnyEvent::DNS for example). + if they were a code reference). Calling them directly is the same as + calling "send". $cv->croak ($error) Similar to send, but causes all call's to "->recv" to invoke "Carp::croak" with the given error message/object/scalar. This can be used to signal any errors to the condition variable - user/consumer. + user/consumer. Doing it this way instead of calling "croak" directly + delays the error detetcion, but has the overwhelmign advantage that + it diagnoses the error at the place where the result is expected, + and not deep in some event clalback without connection to the actual + code causing the problem. $cv->begin ([group callback]) $cv->end - These two methods are EXPERIMENTAL and MIGHT CHANGE. - These two methods can be used to combine many transactions/events into one. For example, a function that pings many hosts in parallel might want to use a condition variable for the whole process. @@ -515,7 +620,38 @@ *supposed* to call "->send", but that is not required. If no callback was set, "send" will be called without any arguments. - Let's clarify this with the ping example: + You can think of "$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; @@ -545,11 +681,11 @@ 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 - subrequests: use an outer "begin"/"end" pair to set the callback and - ensure "end" is called at least once, and then, for each subrequest - you start, call "begin" and for each subrequest you finish, call - "end". + This is the general pattern when you "fan out" into multiple (but + potentially none) subrequests: use an outer "begin"/"end" pair to + set the callback and ensure "end" is called at least once, and then, + for each subrequest you start, call "begin" and for each subrequest + you finish, call "end". METHODS FOR CONSUMERS These methods should only be used by the consuming side, i.e. the code @@ -568,25 +704,21 @@ In list context, all parameters passed to "send" will be returned, in scalar context only the first one will be returned. + Note that doing a blocking wait in a callback is not supported by + any event loop, that is, recursive invocation of a blocking "->recv" + is not allowed, and the "recv" call will "croak" if such a condition + is detected. This condition can be slightly loosened by using + Coro::AnyEvent, which allows you to do a blocking "->recv" from any + thread that doesn't run the event loop itself. + Not all event models support a blocking wait - some die in that case (programs might want to do that to stay interactive), so *if you are - using this from a module, never require a blocking wait*, but let - the caller decide whether the call will block or not (for example, - by coupling condition variables with some kind of request results - and supporting callbacks so the caller knows that getting the result - will not block, while still supporting blocking waits if the caller - so desires). - - Another reason *never* to "->recv" in a module is that you cannot - sensibly have two "->recv"'s in parallel, as that would require - multiple interpreters or coroutines/threads, none of which - "AnyEvent" can supply. - - The Coro module, however, *can* and *does* supply coroutines and, in - fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe - versions and also integrates coroutines into AnyEvent, making - blocking "->recv" calls perfectly safe as long as they are done from - another coroutine (one that doesn't run the event loop). + using this from a module, never require a blocking wait*. Instead, + let the caller decide whether the call will block or not (for + example, by coupling condition variables with some kind of request + results and supporting callbacks so the caller knows that getting + the result will not block, while still supporting blocking waits if + the caller so desires). You can ensure that "-recv" never blocks by setting a callback and only calling "->recv" from within that callback (or at a later @@ -606,48 +738,124 @@ condition variable itself. Calling "recv" inside the callback or at any later time is guaranteed not to block. -GLOBAL VARIABLES AND FUNCTIONS - $AnyEvent::MODEL - Contains "undef" until the first watcher is being created. Then it - contains the event model that is being used, which is the name of - the Perl class implementing the model. This class is usually one of - the "AnyEvent::Impl:xxx" modules, but can be any other class in the - case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). +SUPPORTED EVENT LOOPS/BACKENDS + The available backend classes are (every class has its own manpage): - The known classes so far are: + 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. - AnyEvent::Impl::EV based on EV (an interface to libev, best choice). - AnyEvent::Impl::Event based on Event, second best choice. + 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. - AnyEvent::Impl::Glib based on Glib, third-best choice. - AnyEvent::Impl::Tk based on Tk, very bad choice. - AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). + + Backends that are transparently being picked up when they are used. + These will be used when they are currently loaded when the first + watcher is created, in which case it is assumed that the application + is using them. This means that AnyEvent will automatically pick the + right backend when the main program loads an event module before + anything starts to create watchers. Nothing special needs to be done + by the main program. + + 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, not generic enough for full support. + 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 + otherwise be picked up automatically. As long as the main program + instantiates the application before any AnyEvent watchers are + created, everything should just work. + + AnyEvent::Impl::Qt based on Qt. - 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 - using it's adaptor. + Support for IO::Async can only be partial, as it is too broken and + architecturally limited to even support the AnyEvent API. It also is + the only event loop that needs the loop to be set explicitly, so it + can only be used by a main program knowing about AnyEvent. See + AnyEvent::Impl::Async for the gory details. - AnyEvent knows about Prima and Wx and will try to use POE when - autodetecting them. + AnyEvent::Impl::IOAsync based on IO::Async, cannot be autoprobed. + + Event loops that are indirectly supported via other backends. + Some event loops can be supported via other modules: + + There is no direct support for WxWidgets (Wx) or Prima. + + 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. + + Prima is not supported as nobody seems to be using it, but it has a + POE backend, so it can be supported through POE. + + AnyEvent knows about both Prima and Wx, however, and will try to + load POE when detecting them, in the hope that POE will pick them + up, in which case everything will be automatic. + +GLOBAL VARIABLES AND FUNCTIONS + These are not normally required to use AnyEvent, but can be useful to + write AnyEvent extension modules. + + $AnyEvent::MODEL + Contains "undef" until the first watcher is being created, before + the backend has been autodetected. + + Afterwards it contains the event model that is being used, which is + the name of the Perl class implementing the model. This class is + usually one of the "AnyEvent::Impl:xxx" modules, but can be any + other class in the case AnyEvent has been extended at runtime (e.g. + in *rxvt-unicode* it will be "urxvt::anyevent"). AnyEvent::detect Returns $AnyEvent::MODEL, forcing autodetection of the event model if necessary. You should only call this function right before you would have created an AnyEvent watcher anyway, that is, as late as - possible at runtime. + possible at runtime, and not e.g. while initialising of your module. + + If you need to do some initialisation before AnyEvent watchers are + created, use "post_detect". $guard = AnyEvent::post_detect { BLOCK } Arranges for the code block to be executed as soon as the event model is autodetected (or immediately if this has already happened). + The block will be executed *after* the actual backend has been + detected ($AnyEvent::MODEL is set), but *before* any watchers have + been created, so it is possible to e.g. patch @AnyEvent::ISA or do + other initialisations - see the sources of AnyEvent::Strict or + AnyEvent::AIO to see how this is used. + + The most common usage is to create some global watchers, without + forcing event module detection too early, for example, AnyEvent::AIO + creates and installs the global IO::AIO watcher in a "post_detect" + block to avoid autodetecting the event module at load time. + 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 @@ -655,10 +863,17 @@ after the event loop has been chosen. You should check $AnyEvent::MODEL before adding to this array, - though: if it contains a true value then the event loop has already - been detected, and the array will be ignored. + though: if it is defined then the event loop has already been + 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. - Best use "AnyEvent::post_detect { BLOCK }" instead. + This variable is mainly useful for modules that can do something + useful when AnyEvent is used and thus want to know when it is + initialised, but do not need to even load it by default. This array + provides the means to hook into AnyEvent passively, without loading + it. WHAT TO DO IN A MODULE As a module author, you should "use AnyEvent" and call AnyEvent methods @@ -719,9 +934,9 @@ OTHER MODULES The following is a non-exhaustive list of additional modules that use - AnyEvent and can therefore be mixed easily with other AnyEvent modules - in the same program. Some of the modules come with AnyEvent, some are - available via CPAN. + AnyEvent as a client and can therefore be mixed easily with other + AnyEvent modules and other event loops in the same program. Some of the + modules come with AnyEvent, most are available via CPAN. AnyEvent::Util Contains various utility functions that replace often-used but @@ -737,7 +952,7 @@ 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. + transparent and non-blocking SSL/TLS (via AnyEvent::TLS. AnyEvent::DNS Provides rich asynchronous DNS resolver capabilities. @@ -768,16 +983,18 @@ A non-blocking interface to gpsd, a daemon delivering GPS information. + AnyEvent::IRC + AnyEvent based IRC client module family (replacing the older + Net::IRC3). + + AnyEvent::XMPP + AnyEvent based XMPP (Jabber protocol) module family (replacing the + older Net::XMPP2>. + AnyEvent::IGS A non-blocking interface to the Internet Go Server protocol (used by App::IGS). - Net::IRC3 - AnyEvent based IRC client module family. - - Net::XMPP2 - AnyEvent based XMPP (Jabber protocol) module family. - Net::FCP AnyEvent-based implementation of the Freenet Client Protocol, birthplace of AnyEvent. @@ -788,55 +1005,29 @@ Coro Has special support for AnyEvent via Coro::AnyEvent. - 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. + + 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 @@ -850,17 +1041,23 @@ 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 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" (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, @@ -889,8 +1086,8 @@ 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. @@ -912,6 +1109,69 @@ The maximum number of child processes that "AnyEvent::Util::fork_call" will create in parallel. + "PERL_ANYEVENT_MAX_OUTSTANDING_DNS" + The default value for the "max_outstanding" parameter for the + default DNS resolver - this is the maximum number of parallel DNS + requests that are sent to the DNS server. + + "PERL_ANYEVENT_RESOLV_CONF" + The file to use instead of /etc/resolv.conf (or OS-specific + configuration) in the default resolver. When set to the empty + string, no default config will be used. + + "PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH". + When neither "ca_file" nor "ca_path" was specified during + AnyEvent::TLS context creation, and either of these environment + 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 + 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 @@ -1107,16 +1367,18 @@ 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 @@ -1152,6 +1414,9 @@ 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 @@ -1231,12 +1496,14 @@ 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 @@ -1248,6 +1515,9 @@ 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 @@ -1307,13 +1577,167 @@ * 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. + + Additionally, when AnyEvent is loaded and 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. + +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 epxlains which additional modules will be used, and how + they affect AnyEvent's operetion. + + 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 + This module 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. 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. SECURITY CONSIDERATIONS AnyEvent can be forced to load any event model via @@ -1327,19 +1751,23 @@ 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 @@ -1350,16 +1778,18 @@ 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::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE, + AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi. Non-blocking file handles, sockets, TCP clients and servers: - AnyEvent::Handle, AnyEvent::Socket. + AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS. Asynchronous DNS: AnyEvent::DNS. Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, - Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS. + Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::XMPP, + AnyEvent::HTTP. AUTHOR Marc Lehmann