--- AnyEvent/lib/AnyEvent.pm 2007/11/25 14:08:12 1.38 +++ AnyEvent/lib/AnyEvent.pm 2008/05/10 20:30:35 1.113 @@ -2,7 +2,7 @@ AnyEvent - provide framework for multiple event loops -Event, Coro, Glib, Tk, Perl - various supported event loops +EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops =head1 SYNOPSIS @@ -16,9 +16,57 @@ ... }); - my $w = AnyEvent->condvar; # stores wether a condition was flagged - $w->wait; # enters "main loop" till $condvar gets ->broadcast - $w->broadcast; # wake up current and all future wait's + my $w = AnyEvent->condvar; # stores whether a condition was flagged + $w->wait; # enters "main loop" till $condvar gets ->send + $w->send; # wake up current and all future wait's + +=head1 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? + +Executive Summary: AnyEvent is I, AnyEvent is I and AnyEvent is I. + +First and foremost, I itself, it only +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. + +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 +religion, a way of living, and most importantly: without forcing your +module users into the same thing by forcing them to use the same event +model you use. + +For modules like POE or IO::Async (which is a total misnomer as it is +actually doing all I/O I...), 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 are +I forced to use the same event loop you use. + +AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works +fine. AnyEvent + Tk works fine etc. etc. but none of these work together +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). + +In addition to being free of having to use I, AnyEvent also is free of bloat and policy: with POE or similar +modules, you get an enourmous amount of code and strict rules you have to +follow. AnyEvent, on the other hand, is lean and up to the point, by only +offering the functionality that is necessary, in as thin as a wrapper as +technically possible. + +Of course, if you want lots of policy (this can arguably be somewhat +useful) and you want to force your users to use the one and only event +model, you should I use this module. =head1 DESCRIPTION @@ -27,19 +75,22 @@ users to use the same event loop (as only a single event loop can coexist peacefully at any one time). -The interface itself is vaguely similar but not identical to the Event +The interface itself is vaguely similar, but not identical to the L module. -On the first call of any method, the module tries to detect the currently -loaded event loop by probing wether any of the following modules is -loaded: L, L, L, L. The first one found is -used. If none is found, the module tries to load these modules in the -order given. The first one that could be successfully loaded will be -used. If still none could be found, AnyEvent will fall back to a pure-perl -event loop, which is also not very efficient. +During the first call of any watcher-creation method, the module tries +to detect the currently loaded event loop by probing whether one of the +following modules is already loaded: L, +L, L, L, L, L, L, +L. The first one found is used. If none are found, the module tries +to load these modules (excluding Tk, Event::Lib, Qt and POE as the pure perl +adaptor should always succeed) in the order given. The first one that can +be successfully loaded will be used. If, after this, still none could be +found, AnyEvent will fall back to a pure-perl event loop, which is not +very efficient, but should work everywhere. Because AnyEvent first checks for modules that are already loaded, loading -an Event model explicitly before first using AnyEvent will likely make +an event model explicitly before first using AnyEvent will likely make that model the default. For example: use Tk; @@ -47,6 +98,10 @@ # .. AnyEvent will likely default to Tk +The I means that, if any module loads another event model and +starts using it, all bets are off. Maybe you should tell their authors to +use AnyEvent so their modules work together with others seamlessly... + The pure-perl implementation of AnyEvent is called C. Like other event modules you can load it explicitly. @@ -58,29 +113,52 @@ the callback to call, the filehandle to watch, etc. These watchers are normal Perl objects with normal Perl lifetime. After -creating a watcher it will immediately "watch" for events and invoke -the callback. To disable the watcher you have to destroy it (e.g. by -setting the variable that stores it to C or otherwise deleting all -references to it). +creating a watcher it will immediately "watch" for events and invoke the +callback when the event occurs (of course, only when the event model +is in control). + +To disable the watcher you have to destroy it (e.g. by setting the +variable you store it in to C or otherwise deleting all references +to it). All watchers are created by calling a method on the C class. -=head2 IO WATCHERS - -You can create I/O watcher by calling the C<< AnyEvent->io >> method with -the following mandatory arguments: +Many watchers either are used with "recursion" (repeating timers for +example), or need to refer to their watcher object in other ways. -C the Perl I (not filedescriptor) to watch for -events. C must be a string that is either C or C, that creates -a watcher waiting for "r"eadable or "w"ritable events. C the callback -to invoke everytime the filehandle becomes ready. - -Only one io watcher per C and C combination is allowed (i.e. on -a socket you can have one r + one w, not any more (limitation comes from -Tk - if you are sure you are not using Tk this limitation is gone). +An any way to achieve that is this pattern: -Filehandles will be kept alive, so as long as the watcher exists, the -filehandle exists, too. + my $w; $w = AnyEvent->type (arg => value ..., cb => sub { + # you can use $w here, for example to undef it + undef $w; + }); + +Note that C combination. This is necessary because in Perl, +my variables are only visible after the statement in which they are +declared. + +=head2 I/O WATCHERS + +You can create an I/O watcher by calling the C<< AnyEvent->io >> method +with the following mandatory key-value pairs as arguments: + +C the Perl I (I file descriptor) to watch +for events. C must be a string that is either C or C, +which creates a watcher waiting for "r"eadable or "w"ritable events, +respectively. C is the callback to invoke each time the file handle +becomes ready. + +Although the callback might get passed parameters, their value and +presence is undefined and you cannot rely on them. Portable AnyEvent +callbacks cannot use arguments passed to I/O watcher callbacks. + +The I/O watcher might use the underlying file descriptor or a copy of it. +You must not close a file handle as long as any watcher is active on the +underlying file descriptor. + +Some event loops issue spurious readyness notifications, so you should +always use non-blocking calls when reading/writing from/to your file +handles. Example: @@ -96,8 +174,13 @@ You can create a time watcher by calling the C<< AnyEvent->timer >> method with the following mandatory arguments: -C after how many seconds (fractions are supported) should the timer -activate. C the callback to invoke. +C specifies after how many seconds (fractional values are +supported) the callback should be invoked. C is the callback to invoke +in that case. + +Although the callback might get passed parameters, their value and +presence is undefined and you cannot rely on them. Portable AnyEvent +callbacks cannot use arguments passed to 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 @@ -113,38 +196,160 @@ # to cancel the timer: undef $w; -=head2 CONDITION WATCHERS +Example 2: + + # fire an event after 0.5 seconds, then roughly every second + my $w; -Condition watchers can be created by calling the C<< AnyEvent->condvar >> -method without any arguments. + my $cb = sub { + # cancel the old timer while creating a new one + $w = AnyEvent->timer (after => 1, cb => $cb); + }; -A condition watcher watches for a condition - precisely that the C<< -->broadcast >> method has been called. + # start the "loop" by creating the first watcher + $w = AnyEvent->timer (after => 0.5, cb => $cb); -The watcher has only two methods: +=head3 TIMING ISSUES -=over 4 +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 +o'clock"). + +While most event loops expect timers to specified in a relative way, they +use absolute time internally. This makes a difference when your clock +"jumps", for example, when ntp decides to set your clock backwards from +the wrong date of 2014-01-01 to 2008-01-01, a watcher that is supposed to +fire "after" a second might actually take six years to finally fire. + +AnyEvent cannot compensate for this. The only event loop that is conscious +about these issues is L, which offers both relative (ev_timer, based +on true relative time) and absolute (ev_periodic, based on wallclock time) +timers. -=item $cv->wait +AnyEvent always prefers relative timers, if available, matching the +AnyEvent API. -Wait (blocking if necessary) until the C<< ->broadcast >> method has been -called on c<$cv>, while servicing other watchers normally. +=head2 SIGNAL WATCHERS -Not all event models support a blocking wait - some die in that case, so -if you are using this from a module, never require a blocking wait, but -let the caller decide wether 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 suppporting blockign waits if the caller so desires). +You can watch for signals using a signal watcher, C is the signal +I without any C prefix, C 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 +callbacks cannot use arguments passed to signal watcher callbacks. + +Multiple signal occurances can be clumped together into one callback +invocation, and callback invocation will be synchronous. synchronous means +that it might take a while until the signal gets handled by the process, +but it is guarenteed not to interrupt any other callbacks. -You can only wait once on a condition - additional calls will return -immediately. +The main advantage of using these watchers is that you can share a signal +between multiple watchers. -=item $cv->broadcast +This watcher might use C<%SIG>, so programs overwriting those signals +directly will likely not work correctly. -Flag the condition as ready - a running C<< ->wait >> and all further -calls to C will return after this method has been called. If nobody -is waiting the broadcast will be remembered.. +Example: exit on SIGINT + + my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); + +=head2 CHILD PROCESS WATCHERS + +You can also watch on a child process exit and catch its exit status. + +The child process is specified by the C argument (if set to C<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 C. The callback will be called with the pid +and exit status (as returned by waitpid), so unlike other watcher types, +you I rely on child watcher callback arguments. + +There is a slight catch to child watchers, however: you usually start them +I 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 I handle this correctly, they usually need to be +loaded before the process exits (i.e. before you fork in the first place). + +This means you cannot create a child watcher as the very first thing in an +AnyEvent program, you I to create at least one watcher before you +C the child (alternatively, you can call C). + +Example: fork a process and wait for it + + my $done = AnyEvent->condvar; + + AnyEvent::detect; # force event module to be initialised + + my $pid = fork or exit 5; + + my $w = AnyEvent->child ( + pid => $pid, + cb => sub { + my ($pid, $status) = @_; + warn "pid $pid exited with status $status"; + $done->send; + }, + ); + + # do something else, then wait for process exit + $done->wait; + +=head2 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). + +The instrument to do that is called a "condition variable", so called +because they represent a condition that must become true. + +Condition variables can be created by calling the C<< AnyEvent->condvar +>> method, usually without arguments. The only argument pair allowed is +C, which specifies a callback to be called when the condition variable +becomes true. + +After creation, the conditon variable is "false" until it becomes "true" +by calling the C method. + +Condition variables are similar to callbacks, except that you can +optionally wait for them. They can also be called merge points - points +in time where multiple outstandign events have been processed. And yet +another way to call them is transations - each condition variable can be +used to represent a transaction, which finishes at some point and delivers +a result. + +Condition variables are very useful to signal that something has finished, +for example, if you write a module that does asynchronous http requests, +then a condition variable would be the ideal candidate to signal the +availability of results. The user can either act when the callback is +called or can synchronously C<< ->wait >> for the results. + +You can also use them to simulate traditional event loops - for example, +you can block your main program until an event occurs - for example, you +could C<< ->wait >> in your main program until the user clicks the Quit +button of your app, which would C<< ->send >> the "quit" event. + +Note that condition variables recurse into the event loop - if you have +two pieces of code that call C<< ->wait >> in a round-robbin fashion, you +lose. Therefore, condition variables are good to export to your caller, but +you should avoid making a blocking wait yourself, at least in callbacks, +as this asks for trouble. + +Condition variables are represented by hash refs in perl, and the keys +used by AnyEvent itself are all named C<_ae_XXX> to make subclassing +easy (it is often useful to build your own transaction class on top of +AnyEvent). To subclass, use C as base class and call +it's C method in your own C method. + +There are two "sides" to a condition variable - the "producer side" which +eventually calls C<< -> send >>, and the "consumer side", which waits +for the send to occur. Example: @@ -152,40 +357,161 @@ my $result_ready = AnyEvent->condvar; # do something such as adding a timer - # or socket watcher the calls $result_ready->broadcast + # or socket watcher the calls $result_ready->send # when the "result" is ready. + # in this case, we simply use a timer: + my $w = AnyEvent->timer ( + after => 1, + cb => sub { $result_ready->send }, + ); + # this "blocks" (while handling events) till the callback + # calls send $result_ready->wait; -=back +=head3 METHODS FOR PRODUCERS -=head2 SIGNAL WATCHERS +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 producer side which creates the condvar in most cases, but it isn't +uncommon for the consumer to create it as well. -You can listen for signals using a signal watcher, C is the signal -I without any C prefix. Multiple signals events can be clumped -together into one callback invocation, and callback invocation might or -might not be asynchronous. +=over 4 -These watchers might use C<%SIG>, so programs overwriting those signals -directly will likely not work correctly. +=item $cv->send (...) -Example: exit on SIGINT +Flag the condition as ready - a running C<< ->wait >> and all further +calls to C will (eventually) return after this method has been +called. If nobody is waiting the send will be remembered. - my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); +If a callback has been set on the condition variable, it is called +immediately from within send. -=head2 CHILD PROCESS WATCHERS +Any arguments passed to the C call will be returned by all +future C<< ->wait >> calls. -You can also listen for the status of a child process specified by the -C argument (or any child if the pid argument is 0). The watcher will -trigger as often as status change for the child are received. This works -by installing a signal handler for C. The callback will be called with -the pid and exit status (as returned by waitpid). +=item $cv->croak ($error) -Example: wait for pid 1333 +Similar to send, but causes all call's wait C<< ->wait >> to invoke +C with the given error message/object/scalar. - my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); +This can be used to signal any errors to the condition variable +user/consumer. -=head1 GLOBALS +=item $cv->begin ([group callback]) + +=item $cv->end + +These two methods can be used to combine many transactions/events into +one. For example, a function that pings many hosts in parallel might want +to use a condition variable for the whole process. + +Every call to C<< ->begin >> will increment a counter, and every call to +C<< ->end >> will decrement it. If the counter reaches C<0> in C<< ->end +>>, the (last) callback passed to C will be executed. That callback +is I to call C<< ->send >>, but that is not required. If no +callback was set, C will be called without any arguments. + +Let's clarify this with the ping example: + + my $cv = AnyEvent->condvar; + + my %result; + $cv->begin (sub { $cv->send (\%result) }); + + for my $host (@list_of_hosts) { + $cv->begin; + ping_host_then_call_callback $host, sub { + $result{$host} = ...; + $cv->end; + }; + } + + $cv->end; + +This code fragment supposedly pings a number of hosts and calls +C after results for all then have have been gathered - in any +order. To achieve this, the code issues a call to C when it starts +each ping request and calls C when it has received some result for +it. Since C and C only maintain a counter, the order in which +results arrive is not relevant. + +There is an additional bracketing call to C and C outside the +loop, which serves two important purposes: first, it sets the callback +to be called once the counter reaches C<0>, and second, it ensures that +C is called even when C 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 C/C pair to set the callback and ensure C +is called at least once, and then, for each subrequest you start, call +C and for eahc subrequest you finish, call C. + +=back + +=head3 METHODS FOR CONSUMERS + +These methods should only be used by the consuming side, i.e. the +code awaits the condition. + +=over 4 + +=item $cv->wait + +Wait (blocking if necessary) until the C<< ->send >> or C<< ->croak +>> methods have been called on c<$cv>, while servicing other watchers +normally. + +You can only wait once on a condition - additional calls are valid but +will return immediately. + +If an error condition has been set by calling C<< ->croak >>, then this +function will call C. + +In list context, all parameters passed to C will be returned, +in scalar context only the first one will be returned. + +Not all event models support a blocking wait - some die in that case +(programs might want to do that to stay interactive), so I, 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 suppporting blocking waits if the caller so desires). + +Another reason I to C<< ->wait >> in a module is that you cannot +sensibly have two C<< ->wait >>'s in parallel, as that would require +multiple interpreters or coroutines/threads, none of which C +can supply. + +The L module, however, I and I supply coroutines and, in +fact, L replaces AnyEvent's condvars by coroutine-safe +versions and also integrates coroutines into AnyEvent, making blocking +C<< ->wait >> calls perfectly safe as long as they are done from another +coroutine (one that doesn't run the event loop). + +You can ensure that C<< -wait >> never blocks by setting a callback and +only calling C<< ->wait >> from within that callback (or at a later +time). This will work even when the event loop does not support blocking +waits otherwise. + +=item $bool = $cv->ready + +Returns true when the condition is "true", i.e. whether C or +C have been called. + +=item $cb = $cv->cb ([new callback]) + +This is a mutator function that returns the callback set and optionally +replaces it before doing so. + +The callback will be called when the condition becomes "true", i.e. when +C or C are called. Calling C inside the callback +or at any later time is guaranteed not to block. + +=back + +=head1 GLOBAL VARIABLES AND FUNCTIONS =over 4 @@ -199,51 +525,164 @@ The known classes so far are: - AnyEvent::Impl::CoroEV based on Coro::EV, best choice. - AnyEvent::Impl::EV based on EV (an interface to libev, also best choice). - AnyEvent::Impl::Coro based on Coro::Event, second best choice. - AnyEvent::Impl::Event based on Event, also second best choice :) - AnyEvent::Impl::Glib based on Glib, second-best choice. + AnyEvent::Impl::EV based on EV (an interface to libev, best choice). + AnyEvent::Impl::Event based on Event, second best choice. + AnyEvent::Impl::Perl pure-perl implementation, fast and portable. + AnyEvent::Impl::Glib based on Glib, third-best choice. AnyEvent::Impl::Tk based on Tk, very bad choice. - AnyEvent::Impl::Perl pure-perl implementation, inefficient. + AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). + AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. + AnyEvent::Impl::POE based on POE, not generic enough for full support. + +There is no support for WxWidgets, as WxWidgets has no support for +watching file handles. However, you can use WxWidgets through the +POE Adaptor, as POE has a Wx backend that simply polls 20 times per +second, which was considered to be too horrible to even consider for +AnyEvent. Likewise, other POE backends can be used by AnyEvent by using +it's adaptor. + +AnyEvent knows about L and L and will try to use L when +autodetecting them. =item AnyEvent::detect -Returns C<$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, very late at runtime. +Returns C<$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. + +=item $guard = AnyEvent::post_detect { BLOCK } + +Arranges for the code block to be executed as soon as the event model is +autodetected (or immediately if this has already happened). + +If called in scalar or list context, then it creates and returns an object +that automatically removes the callback again when it is destroyed. See +L for a case where this is useful. + +=item @AnyEvent::post_detect + +If there are any code references in this array (you can C to it +before or after loading AnyEvent), then they will called directly after +the event loop has been chosen. + +You should check C<$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. + +Best use C instead. =back =head1 WHAT TO DO IN A MODULE -As a module author, you should "use AnyEvent" and call AnyEvent methods +As a module author, you should C and call AnyEvent methods freely, but you should not load a specific event module or rely on it. -Be careful when you create watchers in the module body - Anyevent will +Be careful when you create watchers in the module body - AnyEvent will decide which event module to use as soon as the first method is called, so by calling AnyEvent in your module body you force the user of your module to load the event module first. +Never call C<< ->wait >> on a condition variable unless you I that +the C<< ->send >> method has been called on it already. This is +because it will stall the whole program, and the whole point of using +events is to stay interactive. + +It is fine, however, to call C<< ->wait >> when the user of your module +requests it (i.e. if you create a http request object ad have a method +called C that returns the results, it should call C<< ->wait >> +freely, as the user of your module knows what she is doing. always). + =head1 WHAT TO DO IN THE MAIN PROGRAM There will always be a single main program - the only place that should dictate which event model to use. If it doesn't care, it can just "use AnyEvent" and use it itself, or not -do anything special and let AnyEvent decide which implementation to chose. +do anything special (it does not need to be event-based) and let AnyEvent +decide which implementation to chose if some module relies on it. -If the main program relies on a specific event model (for example, in Gtk2 -programs you have to rely on either Glib or Glib::Event), you should load -it before loading AnyEvent or any module that uses it, generally, as early -as possible. The reason is that modules might create watchers when they -are loaded, and AnyEvent will decide on the event model to use as soon as -it creates watchers, and it might chose the wrong one unless you load the -correct one yourself. +If the main program relies on a specific event model. For example, in +Gtk2 programs you have to rely on the Glib module. You should load the +event module before loading AnyEvent or any module that uses it: generally +speaking, you should load it as early as possible. The reason is that +modules might create watchers when they are loaded, and AnyEvent will +decide on the event model to use as soon as it creates watchers, and it +might chose the wrong one unless you load the correct one yourself. You can chose to use a rather inefficient pure-perl implementation by -loading the C module, but letting AnyEvent chose is -generally better. +loading the C module, which gives you similar +behaviour everywhere, but letting AnyEvent chose is generally better. + +=head1 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. + +=over 4 + +=item L + +Contains various utility functions that replace often-used but blocking +functions such as C by event-/callback-based versions. + +=item L + +Provide read and write buffers and manages watchers for reads and writes. + +=item L + +Provides a simple web application server framework. + +=item L + +Provides asynchronous DNS resolver capabilities, beyond what +L offers. + +=item L + +The fastest ping in the west. + +=item L + +AnyEvent based IRC client module family. + +=item L + +AnyEvent based XMPP (Jabber protocol) module family. + +=item L + +AnyEvent-based implementation of the Freenet Client Protocol, birthplace +of AnyEvent. + +=item L + +High level API for event-based execution flow control. + +=item L + +Has special support for AnyEvent via L. + +=item L, L + +Truly asynchronous I/O, should be in the toolbox of every event +programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent +together. + +=item L, L + +Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently fuses +IO::AIO and AnyEvent together. + +=item L + +The lambda approach to I/O - don't ask, look there. Can use AnyEvent. + +=back =cut @@ -254,7 +693,7 @@ use Carp; -our $VERSION = '2.8'; +our $VERSION = '3.4'; our $MODEL; our $AUTOLOAD; @@ -265,53 +704,93 @@ our @REGISTRY; my @models = ( - [Coro::EV:: => AnyEvent::Impl::CoroEV::], [EV:: => AnyEvent::Impl::EV::], - [Coro::Event:: => AnyEvent::Impl::Coro::], [Event:: => AnyEvent::Impl::Event::], - [Glib:: => AnyEvent::Impl::Glib::], [Tk:: => AnyEvent::Impl::Tk::], + [Wx:: => AnyEvent::Impl::POE::], + [Prima:: => AnyEvent::Impl::POE::], [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], + # everything below here will not be autoprobed as the pureperl backend should work everywhere + [Glib:: => AnyEvent::Impl::Glib::], + [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy + [Qt:: => AnyEvent::Impl::Qt::], # requires special main program + [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza ); -our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY); +our %method = map +($_ => 1), qw(io timer signal child condvar one_event DESTROY); + +our @post_detect; + +sub post_detect(&) { + my ($cb) = @_; + + if ($MODEL) { + $cb->(); + + 1 + } else { + push @post_detect, $cb; + + defined wantarray + ? bless \$cb, "AnyEvent::Util::Guard" + : () + } +} + +sub AnyEvent::Util::Guard::DESTROY { + @post_detect = grep $_ != ${$_[0]}, @post_detect; +} sub detect() { unless ($MODEL) { no strict 'refs'; - # check for already loaded models - for (@REGISTRY, @models) { - my ($package, $model) = @$_; - if (${"$package\::VERSION"} > 0) { - if (eval "require $model") { - $MODEL = $model; - warn "AnyEvent: found model '$model', using it.\n" if $verbose > 1; - last; - } + if ($ENV{PERL_ANYEVENT_MODEL} =~ /^([a-zA-Z]+)$/) { + my $model = "AnyEvent::Impl::$1"; + if (eval "require $model") { + $MODEL = $model; + warn "AnyEvent: loaded model '$model' (forced by \$PERL_ANYEVENT_MODEL), using it.\n" if $verbose > 1; + } else { + warn "AnyEvent: unable to load model '$model' (from \$PERL_ANYEVENT_MODEL):\n$@" if $verbose; } } + # check for already loaded models unless ($MODEL) { - # try to load a model - for (@REGISTRY, @models) { my ($package, $model) = @$_; - if (eval "require $package" - and ${"$package\::VERSION"} > 0 - and eval "require $model") { - $MODEL = $model; - warn "AnyEvent: autoprobed and loaded model '$model', using it.\n" if $verbose > 1; - last; + if (${"$package\::VERSION"} > 0) { + if (eval "require $model") { + $MODEL = $model; + warn "AnyEvent: autodetected model '$model', using it.\n" if $verbose > 1; + last; + } } } - $MODEL - or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV (or Coro+EV), Event (or Coro+Event), Glib or Tk."; + unless ($MODEL) { + # try to load a model + + for (@REGISTRY, @models) { + my ($package, $model) = @$_; + if (eval "require $package" + and ${"$package\::VERSION"} > 0 + and eval "require $model") { + $MODEL = $model; + warn "AnyEvent: autoprobed model '$model', using it.\n" if $verbose > 1; + last; + } + } + + $MODEL + or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: EV, Event or Glib."; + } } unshift @ISA, $MODEL; push @{"$MODEL\::ISA"}, "AnyEvent::Base"; + + (shift @post_detect)->() while @post_detect; } $MODEL @@ -428,61 +907,104 @@ =head1 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 C<@AnyEvent::REGISTRY>. You can do that before and even without loading -AnyEvent. +AnyEvent, so it is reasonably cheap. Example: push @AnyEvent::REGISTRY, [urxvt => urxvt::anyevent::]; This tells AnyEvent to (literally) use the C -package/class when it finds the C package/module is loaded. When -AnyEvent is loaded and asked to find a suitable event model, it will -first check for the presence of urxvt. - -The class should provide implementations for all watcher types (see -L (source code), L -(Source code) and so on for actual examples, use C to see the sources). - -The above isn't fictitious, the I (a.k.a. urxvt) -uses the above line as-is. An interface isn't included in AnyEvent -because it doesn't make sense outside the embedded interpreter inside -I, and it is updated and maintained as part of the +package/class when it finds the C 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 C the +C module. + +The class should provide implementations for all watcher types. See +L (source code), L (Source code) +and so on for actual examples. Use C to +see the sources. + +If you don't provide C and C watchers than AnyEvent will +provide suitable (hopefully) replacements. + +The above example isn't fictitious, the I (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 I, and it is updated and maintained as part of the I distribution. I also cheats a bit by not providing blocking access to condition variables: code blocking while waiting for a condition will C. This still works with most modules/usages, and blocking calls must -not be in an interactive application, so it makes sense. +not be done in an interactive application, so it makes sense. =head1 ENVIRONMENT VARIABLES The following environment variables are used by this module: -C when set to C<2> or higher, reports which event -model gets used. +=over 4 + +=item C + +By default, AnyEvent will be completely silent except in fatal +conditions. You can set this environment variable to make AnyEvent more +talkative. + +When set to C<1> or higher, causes AnyEvent to warn about unexpected +conditions, such as not being able to load the event model specified by +C. + +When set to C<2> or higher, cause AnyEvent to report to STDERR which event +model it chooses. + +=item C + +This can be used to specify the event model to be used by AnyEvent, before +autodetection and -probing kicks in. It must be a string consisting +entirely of ASCII letters. The string C gets prepended +and the resulting module name is loaded and if the load was successful, +used as event model. If it fails to load AnyEvent will proceed with +autodetection and -probing. + +This functionality might change in future versions. + +For example, to force the pure perl model (L) you +could start your program like this: -=head1 EXAMPLE + PERL_ANYEVENT_MODEL=Perl perl ... -The following program uses an io watcher to read data from stdin, a timer -to display a message once per second, and a condvar to exit the program -when the user enters quit: +=back + +=head1 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 quit the +program when the user enters quit: use AnyEvent; my $cv = AnyEvent->condvar; - my $io_watcher = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { - warn "io event <$_[0]>\n"; # will always output - chomp (my $input = ); # read a line - warn "read: $input\n"; # output what has been read - $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i - }); + my $io_watcher = AnyEvent->io ( + fh => \*STDIN, + poll => 'r', + cb => sub { + warn "io event <$_[0]>\n"; # will always output + chomp (my $input = ); # read a line + warn "read: $input\n"; # output what has been read + $cv->broadcast if $input =~ /^q/i; # quit program if /^q/i + }, + ); my $time_watcher; # can only be used once @@ -574,7 +1096,7 @@ The actual code goes further and collects all errors (Cs, exceptions) that occured during request processing. The C method detects -wether an exception as thrown (it is stored inside the $txn object) +whether an exception as thrown (it is stored inside the $txn object) and just throws the exception, which means connection errors and other problems get reported tot he code that tries to use the result, not in a random callback. @@ -585,7 +1107,7 @@ my $data = $fcp->client_get ($url); -2. Blocking, but parallelizing: +2. Blocking, but running in parallel: my @datas = map $_->result, map $fcp->txn_client_get ($_), @@ -594,9 +1116,9 @@ Both blocking examples work without the module user having to know anything about events. -3a. Event-based in a main program, using any support Event module: +3a. Event-based in a main program, using any supported event module: - use Event; + use EV; $fcp->txn_client_get ($url)->cb (sub { my $txn = shift; @@ -604,7 +1126,7 @@ ... }); - Event::loop; + EV::loop; 3b. The module user could use AnyEvent, too: @@ -619,15 +1141,323 @@ $quit->wait; + +=head1 BENCHMARKS + +To give you an idea of the performance and overheads that AnyEvent adds +over the event loops themselves and to give you an impression of the speed +of various event loops I prepared some benchmarks. + +=head2 BENCHMARKING ANYEVENT OVERHEAD + +Here is a benchmark of various supported event models used natively and +through anyevent. The benchmark creates a lot of timers (with a zero +timeout) and I/O watchers (watching STDOUT, a pty, to become writable, +which it is), lets them fire exactly once and destroys them again. + +Source code for this benchmark is found as F in the AnyEvent +distribution. + +=head3 Explanation of the columns + +I is the number of event watchers created/destroyed. Since +different event models feature vastly different performances, each event +loop was given a number of watchers so that overall runtime is acceptable +and similar between tested event loop (and keep them from crashing): Glib +would probably take thousands of years if asked to process the same number +of watchers as EV in this benchmark. + +I is the number of bytes (as measured by the resident set size, +RSS) consumed by each watcher. This method of measuring captures both C +and Perl-based overheads. + +I is the time, in microseconds (millionths of seconds), that it +takes to create a single watcher. The callback is a closure shared between +all watchers, to avoid adding memory overhead. That means closure creation +and memory usage is not included in the figures. + +I is the time, in microseconds, used to invoke a simple +callback. The callback simply counts down a Perl variable and after it was +invoked "watcher" times, it would C<< ->broadcast >> a condvar once to +signal the end of this phase. + +I is the time, in microseconds, that it takes to destroy a single +watcher. + +=head3 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 + +=head3 Discussion + +The benchmark does I measure scalability of the event loop very +well. For example, a select-based event loop (such as the pure perl one) +can never compete with an event loop that uses epoll when the number of +file descriptors grows high. In this benchmark, all events become ready at +the same time, so select/poll-based implementations get an unnatural speed +boost. + +Also, note that the number of watchers usually has a nonlinear effect on +overall speed, that is, creating twice as many watchers doesn't take twice +the time - usually it takes longer. This puts event loops tested with a +higher number of watchers at a disadvantage. + +To put the range of results into perspective, consider that on the +benchmark machine, handling an event takes roughly 1600 CPU cycles with +EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 CPU +cycles with POE. + +C 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. + +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 perl +interpreter and the backend itself). Nevertheless this shows that it +adds very little overhead in itself. Like any select-based backend its +performance becomes really bad with lots of file descriptors (and few of +them active), of course, but this was not subject of this benchmark. + +The C module has a relatively high setup and callback invocation +cost, but overall scores in on the third place. + +C's memory usage is quite a bit higher, but it features a +faster callback invocation and overall ends up in the same class as +C. However, Glib scales extremely badly, doubling the number of +watchers increases the processing time by more than a factor of four, +making it completely unusable when using larger numbers of watchers +(note that only a single file descriptor was used in the benchmark, so +inefficiencies of C do not account for this). + +The C adaptor works relatively well. The fact that it crashes with +more than 2000 watchers is a big setback, however, as correctness takes +precedence over speed. Nevertheless, its performance is surprising, as the +file descriptor is dup()ed for each watcher. This shows that the dup() +employed by some adaptors is not a big performance issue (it does incur a +hidden memory cost inside the kernel which is not reflected in the figures +above). + +C, regardless of underlying event loop (whether using its pure perl +select-based backend or the Event module, the POE-EV backend couldn't +be tested because it wasn't working) shows abysmal performance and +memory usage with AnyEvent: Watchers use almost 30 times as much memory +as EV watchers, and 10 times as much memory as Event (the high memory +requirements are caused by requiring a session for each watcher). Watcher +invocation speed is almost 900 times slower than with AnyEvent's pure perl +implementation. + +The design of the POE adaptor class in AnyEvent can not really account +for the performance issues, though, as session creation overhead is +small compared to execution of the state machine, which is coded pretty +optimally within L (and while everybody agrees that +using multiple sessions is not a good approach, especially regarding +memory usage, even the author of POE could not come up with a faster +design). + +=head3 Summary + +=over 4 + +=item * Using EV through AnyEvent is faster than any other event loop +(even when used without AnyEvent), but most event loops have acceptable +performance with or without AnyEvent. + +=item * The overhead AnyEvent adds is usually much smaller than the overhead of +the actual event loop, only with extremely fast event loops such as EV +adds AnyEvent significant overhead. + +=item * You should avoid POE like the plague if you want performance or +reasonable memory usage. + +=back + +=head2 BENCHMARKING THE LARGE SERVER CASE + +This benchmark atcually benchmarks the event loop itself. It works by +creating a number of "servers": each server consists of a socketpair, a +timeout watcher that gets reset on activity (but never fires), and an I/O +watcher waiting for input on one side of the socket. Each time the socket +watcher reads a byte it will write that byte to a random other "server". + +The effect is that there will be a lot of I/O watchers, only part of which +are active at any one point (so there is a constant number of active +fds for each loop iterstaion, but which fds these are is random). The +timeout is reset each time something is read because that reflects how +most timeouts work (and puts extra pressure on the event loops). + +In this benchmark, we use 10000 socketpairs (20000 sockets), of which 100 +(1%) are active. This mirrors the activity of large servers with many +connections, most of which are idle at any one point in time. + +Source code for this benchmark is found as F in the AnyEvent +distribution. + +=head3 Explanation of the columns + +I is the number of sockets, and twice the number of "servers" (as +each server has a read and write socket end). + +I is the time it takes to create a socketpair (which is +nontrivial) and two watchers: an I/O watcher and a timeout watcher. + +I, the most important value, is the time it takes to handle a +single "request", that is, reading the token from the pipe and forwarding +it to another server. This includes deleting the old timeout and creating +a new one that moves the timeout into the future. + +=head3 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 + +=head3 Discussion + +This benchmark I measure scalability and overall performance of the +particular event loop. + +EV is again fastest. Since it is using epoll on my system, the setup time +is relatively high, though. + +Perl surprisingly comes second. It is much faster than the C-based event +loops Event and Glib. + +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 C<< $_->() for .. >>-style loop that the Perl event loop uses. Event +uses select or poll in basically all documented configurations. + +Glib is hit hard by its quadratic behaviour w.r.t. many watchers. It +clearly fails to perform with many filehandles or in busy servers. + +POE is still completely out of the picture, taking over 1000 times as long +as EV, and over 100 times as long as the Perl implementation, even though +it uses a C-based event loop in this case. + +=head3 Summary + +=over 4 + +=item * The pure perl implementation performs extremely well. + +=item * Avoid Glib or POE in large projects where performance matters. + +=back + +=head2 BENCHMARKING SMALL SERVERS + +While event loops should scale (and select-based ones do not...) even to +large servers, most programs we (or I :) actually write have only a few +I/O watchers. + +In this benchmark, I use the same benchmark program as in the large server +case, but it uses only eight "servers", of which three are active at any +one time. This should reflect performance for a small server relatively +well. + +The columns are identical to the previous table. + +=head3 Results + + name sockets create request + EV 16 20.00 6.54 + Perl 16 25.75 12.62 + Event 16 81.27 35.86 + Glib 16 32.63 15.48 + POE 16 261.87 276.28 uses POE::Loop::Event + +=head3 Discussion + +The benchmark tries to test the performance of a typical small +server. While knowing how various event loops perform is interesting, keep +in mind that their overhead in this case is usually not as important, due +to the small absolute number of watchers (that is, you need efficiency and +speed most when you have lots of watchers, not when you only have a few of +them). + +EV is again fastest. + +Perl again comes second. It is noticably faster than the C-based event +loops Event and Glib, although the difference is too small to really +matter. + +POE also performs much better in this case, but is is still far behind the +others. + +=head3 Summary + +=over 4 + +=item * C-based event loops perform very well with small number of +watchers, as the management overhead dominates. + +=back + + +=head1 FORK + +Most event libraries are not fork-safe. The ones who are usually are +because they rely on inefficient but fork-safe C