--- AnyEvent/README 2008/04/28 08:02:14 1.19 +++ AnyEvent/README 2008/09/29 02:08:57 1.30 @@ -1,23 +1,37 @@ NAME AnyEvent - provide framework for multiple event loops - EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - - various supported event loops + EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event + loops SYNOPSIS use AnyEvent; - my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { - ... - }); + my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { ... }); + + my $w = AnyEvent->timer (after => $seconds, cb => sub { ... }); + my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ... + + print AnyEvent->now; # prints current event loop time + print AnyEvent->time; # think Time::HiRes::time or simply CORE::time. + + my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... }); - my $w = AnyEvent->timer (after => $seconds, cb => sub { + my $w = AnyEvent->child (pid => $pid, cb => sub { + my ($pid, $status) = @_; ... }); my $w = AnyEvent->condvar; # stores whether a condition was flagged - $w->wait; # enters "main loop" till $condvar gets ->broadcast - $w->broadcast; # wake up current and all future wait's + $w->send; # wake up current and all future recv's + $w->recv; # enters "main loop" till $condvar gets ->send + # use a condvar in callback mode: + $w->cb (sub { $_[0]->recv }); + +INTRODUCTION/TUTORIAL + This manpage is mainly a reference manual. If you are interested in a + tutorial or some gentle introduction, have a look at the AnyEvent::Intro + manpage. WHY YOU SHOULD USE THIS MODULE (OR NOT) Glib, POE, IO::Async, Event... CPAN offers event models by the dozen @@ -27,11 +41,12 @@ policy* and AnyEvent is *small and efficient*. First and foremost, *AnyEvent is not an event model* itself, it only - interfaces to whatever event model the main program happens to use in a + interfaces to whatever event model the main program happens to use, in a pragmatic way. For event models and certain classes of immortals alike, the statement "there can only be one" is a bitter reality: In general, only one event loop can be active at the same time in a process. - AnyEvent helps hiding the differences between those event loops. + AnyEvent cannot change this, but it can hide the differences between + those event loops. The goal of AnyEvent is to offer module authors the ability to do event programming (waiting for I/O or timer events) without subscribing to a @@ -42,27 +57,33 @@ For modules like POE or IO::Async (which is a total misnomer as it is actually doing all I/O *synchronously*...), using them in your module is like joining a cult: After you joined, you are dependent on them and you - cannot use anything else, as it is simply incompatible to everything - that isn't itself. What's worse, all the potential users of your module + cannot use anything else, as they are simply incompatible to everything + that isn't them. What's worse, all the potential users of your module are *also* forced to use the same event loop you use. AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works 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 + with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your module uses one of those, every user of your module has to use it, too. But if your module uses AnyEvent, it works transparently with all event - models it supports (including stuff like POE and IO::Async, as long as - those use one of the supported event loops. It is trivial to add new - event loops to AnyEvent, too, so it is future-proof). + models it supports (including stuff like IO::Async, as long as those use + one of the supported event loops. It is trivial to add new event loops + to AnyEvent, too, so it is future-proof). In addition to being free of having to use *the one and only true event model*, AnyEvent also is free of bloat and policy: with POE or similar - 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 + modules, you get an enormous 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 + Of course, AnyEvent comes with a big (and fully optional!) toolbox of + useful functionality, such as an asynchronous DNS resolver, 100% + non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms + such as Windows) and lots of real-world knowledge and workarounds for + platform bugs and differences. + + Now, if you *do 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 *not* use this module. @@ -77,9 +98,9 @@ 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: Coro::EV, Coro::Event, EV, Event, - Glib, AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found - is used. If none are found, the module tries to load these modules + following modules is already loaded: EV, Event, Glib, + AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. 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 @@ -101,12 +122,12 @@ The pure-perl implementation of AnyEvent is called "AnyEvent::Impl::Perl". Like other event modules you can load it - explicitly. + explicitly and enjoy the high availability of that event loop :) WATCHERS AnyEvent has the central concept of a *watcher*, which is an object that stores relevant data for each kind of event you are waiting for, such as - the callback to call, the filehandle to watch, etc. + the callback to call, the file handle 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 @@ -124,10 +145,10 @@ An any way to achieve that is this pattern: - my $w; $w = AnyEvent->type (arg => value ..., cb => sub { - # you can use $w here, for example to undef it - undef $w; - }); + my $w; $w = AnyEvent->type (arg => value ..., cb => sub { + # you can use $w here, for example to undef it + undef $w; + }); Note that "my $w; $w =" combination. This is necessary because in Perl, my variables are only visible after the statement in which they are @@ -137,7 +158,8 @@ You can create an I/O watcher by calling the "AnyEvent->io" method with the following mandatory key-value pairs as arguments: - "fh" the Perl *file handle* (*not* file descriptor) to watch for events. + "fh" the Perl *file handle* (*not* file descriptor) to watch for events + (AnyEvent might or might not keep a reference to this file handle). "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. @@ -154,9 +176,9 @@ always use non-blocking calls when reading/writing from/to your file handles. - Example: + Example: wait for readability of STDIN, then read a line and disable the + watcher. - # wait for readability of STDIN, then read a line and disable the watcher my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { chomp (my $input = ); warn "read: $input\n"; @@ -175,13 +197,18 @@ presence is undefined and you cannot rely on them. Portable AnyEvent callbacks cannot use arguments passed to time watcher callbacks. - The timer callback will be invoked at most once: if you want a repeating - timer you have to create a new watcher (this is a limitation by both Tk - and Glib). + The callback will normally be invoked once only. If you specify another + parameter, "interval", as a strictly positive number (> 0), then the + callback will be invoked regularly at that interval (in fractional + seconds) after the first invocation. If "interval" is specified with a + false value, then it is treated as if it were missing. + + The callback will be rescheduled before invoking the callback, but no + attempt is done to avoid timer drift in most backends, so the interval + is only approximate. - Example: + Example: fire an event after 7.7 seconds. - # fire an event after 7.7 seconds my $w = AnyEvent->timer (after => 7.7, cb => sub { warn "timeout\n"; }); @@ -189,19 +216,12 @@ # to cancel the timer: undef $w; - Example 2: - - # fire an event after 0.5 seconds, then roughly every second - my $w; + Example 2: fire an event after 0.5 seconds, then roughly every second. - my $cb = sub { - # cancel the old timer while creating a new one - $w = AnyEvent->timer (after => 1, cb => $cb); + my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub { + warn "timeout\n"; }; - # start the "loop" by creating the first watcher - $w = AnyEvent->timer (after => 0.5, cb => $cb); - TIMING ISSUES There are two ways to handle timers: based on real time (relative, "fire in 10 seconds") and based on wallclock time (absolute, "fire at 12 @@ -222,19 +242,81 @@ AnyEvent always prefers relative timers, if available, matching the AnyEvent API. + AnyEvent has two additional methods that return the "current time": + + AnyEvent->time + This returns the "current wallclock time" as a fractional number of + seconds since the Epoch (the same thing as "time" or + "Time::HiRes::time" return, and the result is guaranteed to be + compatible with those). + + It progresses independently of any event loop processing, i.e. each + call will check the system clock, which usually gets updated + frequently. + + AnyEvent->now + This also returns the "current wallclock time", but unlike "time", + above, this value might change only once per event loop iteration, + depending on the event loop (most return the same time as "time", + above). This is the time that AnyEvent's timers get scheduled + against. + + *In almost all cases (in all cases if you don't care), this is the + function to call when you want to know the current time.* + + This function is also often faster then "AnyEvent->time", and thus + the preferred method if you want some timestamp (for example, + AnyEvent::Handle uses this to update it's activity timeouts). + + The rest of this section is only of relevance if you try to be very + exact with your timing, you can skip it without bad conscience. + + For a practical example of when these times differ, consider + Event::Lib and EV and the following set-up: + + The event loop is running and has just invoked one of your callback + at time=500 (assume no other callbacks delay processing). In your + callback, you wait a second by executing "sleep 1" (blocking the + process for a second) and then (at time=501) you create a relative + timer that fires after three seconds. + + With Event::Lib, "AnyEvent->time" and "AnyEvent->now" will both + return 501, because that is the current time, and the timer will be + scheduled to fire at time=504 (501 + 3). + + With EV, "AnyEvent->time" returns 501 (as that is the current time), + but "AnyEvent->now" returns 500, as that is the time the last event + processing phase started. With EV, your timer gets scheduled to run + at time=503 (500 + 3). + + In one sense, Event::Lib is more exact, as it uses the current time + regardless of any delays introduced by event processing. However, + most callbacks do not expect large delays in processing, so this + causes a higher drift (and a lot more system calls to get the + current time). + + In another sense, EV is more exact, as your timer will be scheduled + at the same time, regardless of how long event processing actually + took. + + In either case, if you care (and in most cases, you don't), then you + can get whatever behaviour you want with any event loop, by taking + the difference between "AnyEvent->time" and "AnyEvent->now" into + account. + SIGNAL WATCHERS You can watch for signals using a signal watcher, "signal" is the signal - *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked - whenever a signal occurs. + *name* in uppercase and without any "SIG" prefix, "cb" is the Perl + callback to be invoked whenever a signal occurs. Although the callback might get passed parameters, their value and presence is undefined and you cannot rely on them. Portable AnyEvent 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 + Multiple signal occurrences 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. + 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. @@ -250,11 +332,18 @@ You can also watch on a child process exit and catch its exit status. The child process is specified by the "pid" argument (if set to 0, it - watches for any child process exit). The watcher will trigger as often - as status change for the child are received. This works by installing a - signal handler for "SIGCHLD". The callback will be called with the pid - and exit status (as returned by waitpid), so unlike other watcher types, - you *can* rely on child watcher callback arguments. + watches for any child process exit). The watcher will triggered only + when the child process has finished and an exit status is available, not + on any trace events (stopped/continued). + + The callback will be called with the pid and exit status (as returned by + waitpid), so unlike other watcher types, you *can* rely on child watcher + callback arguments. + + This watcher type works by installing a signal handler for "SIGCHLD", + and since it cannot be shared, nothing else should use SIGCHLD or reap + random child processes (waiting for specific child processes, e.g. + inside "system", is just fine). There is a slight catch to child watchers, however: you usually start them *after* the child process was created, and this means the process @@ -271,55 +360,220 @@ Example: fork a process and wait for it - my $done = AnyEvent->condvar; - - AnyEvent::detect; # force event module to be initialised + my $done = AnyEvent->condvar; + + 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->recv; - my $pid = fork or exit 5; + 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. - my $w = AnyEvent->child ( - pid => $pid, - cb => sub { - my ($pid, $status) = @_; - warn "pid $pid exited with status $status"; - $done->broadcast; - }, - ); + AnyEvent is different, it expects somebody else to run the event loop + and will only block when necessary (usually when told by the user). - # do something else, then wait for process exit - $done->wait; + The instrument to do that is called a "condition variable", so called + because they represent a condition that must become true. - CONDITION VARIABLES Condition variables can be created by calling the "AnyEvent->condvar" - method without any arguments. + method, usually without arguments. The only argument pair allowed is - A condition variable waits for a condition - precisely that the - "->broadcast" method has been called. - - They are very useful to signal that a condition has been fulfilled, 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. - - You can also use condition variables to block your main program until an - event occurs - for example, you could "->wait" in your main program - until the user clicks the Quit button in your app, which would - "->broadcast" the "quit" event. + "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). + + After creation, the condition variable is "false" until it becomes + "true" by calling the "send" method (or calling the condition variable + as if it were a callback, read about the caveats in the description for + the "->send" 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 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. + + 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 "->recv" 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 "->recv" in your main program until the user clicks the Quit + button of your app, which would "->send" the "quit" event. Note that condition variables recurse into the event loop - if you have - two pirces of code that call "->wait" in a round-robbin fashion, you + two pieces of code that call "->recv" in a round-robin 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. - This object has two methods: + Condition variables are represented by hash refs in perl, and the keys + used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy + (it is often useful to build your own transaction class on top of + AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call + it's "new" method in your own "new" method. + + There are two "sides" to a condition variable - the "producer side" + which eventually calls "-> send", and the "consumer side", which waits + for the send to occur. + + Example: wait for a timer. + + # wait till the result is ready + my $result_ready = AnyEvent->condvar; + + # do something such as adding a timer + # 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->recv; + + Example: wait for a timer, but take advantage of the fact that condition + variables are also code references. - $cv->wait - Wait (blocking if necessary) until the "->broadcast" method has been - called on c<$cv>, while servicing other watchers normally. + my $done = AnyEvent->condvar; + my $delay = AnyEvent->timer (after => 5, cb => $done); + $done->recv; - You can only wait once on a condition - additional calls will return - immediately. + Example: Imagine an API that returns a condvar and doesn't support + callbacks. This is how you make a synchronous call, for example from the + main program: + + use AnyEvent::CouchDB; + + ... + + my @info = $couchdb->info->recv; + + And this is how you would just ste a callback to be called whenever the + results are available: + + $couchdb->info->cb (sub { + my @info = $_[0]->recv; + }); + + METHODS FOR PRODUCERS + These methods should only be used by the producing side, i.e. the + code/module that eventually sends the signal. Note that it is also the + producer side which creates the condvar in most cases, but it isn't + uncommon for the consumer to create it as well. + + $cv->send (...) + Flag the condition as ready - a running "->recv" and all further + calls to "recv" will (eventually) return after this method has been + called. If nobody is waiting the send will be remembered. + + If a callback has been set on the condition variable, it is called + immediately from within send. + + Any arguments passed to the "send" call will be returned by all + 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). + + $cv->croak ($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. + + $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. + + Every call to "->begin" will increment a counter, and every call to + "->end" will decrement it. If the counter reaches 0 in "->end", the + (last) callback passed to "begin" will be executed. That callback is + *supposed* to call "->send", but that is not required. If no + callback was set, "send" will be called without any arguments. + + 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 + "send" after results for all then have have been gathered - in any + order. To achieve this, the code issues a call to "begin" when it + starts each ping request and calls "end" when it has received some + result for it. Since "begin" and "end" only maintain a counter, the + order in which results arrive is not relevant. + + There is an additional bracketing call to "begin" and "end" outside + the loop, which serves two important purposes: first, it sets the + callback to be called once the counter reaches 0, and second, it + 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". + + METHODS FOR CONSUMERS + These methods should only be used by the consuming side, i.e. the code + awaits the condition. + + $cv->recv + Wait (blocking if necessary) until the "->send" or "->croak" methods + have been called on c<$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 "->croak", then this + function will call "croak". + + In list context, all parameters passed to "send" 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 *if you are @@ -327,38 +581,37 @@ 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 + will not block, while still supporting blocking waits if the caller so desires). - Another reason *never* to "->wait" in a module is that you cannot - sensibly have two "->wait"'s in parallel, as that would require + 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 coroutine-aware backends - AnyEvent::Impl::CoroEV and AnyEvent::Impl::CoroEvent explicitly - support concurrent "->wait"'s from different coroutines, however). - - $cv->broadcast - Flag the condition as ready - a running "->wait" and all further - calls to "wait" will (eventually) return after this method has been - called. If nobody is waiting the broadcast will be remembered.. - - Example: + "AnyEvent" can supply. - # wait till the result is ready - my $result_ready = AnyEvent->condvar; - - # do something such as adding a timer - # or socket watcher the calls $result_ready->broadcast - # when the "result" is ready. - # in this case, we simply use a timer: - my $w = AnyEvent->timer ( - after => 1, - cb => sub { $result_ready->broadcast }, - ); - - # this "blocks" (while handling events) till the watcher - # calls broadcast - $result_ready->wait; + 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). + + You can ensure that "-recv" never blocks by setting a callback and + only calling "->recv" from within that callback (or at a later + time). This will work even when the event loop does not support + blocking waits otherwise. + + $bool = $cv->ready + Returns true when the condition is "true", i.e. whether "send" or + "croak" have been called. + + $cb = $cv->cb ($cb->($cv)) + This is a mutator function that returns the callback set and + optionally replaces it before doing so. + + The callback will be called when the condition becomes "true", i.e. + when "send" or "croak" are called, with the only argument being the + condition variable itself. Calling "recv" inside the callback or at + any later time is guaranteed not to block. GLOBAL VARIABLES AND FUNCTIONS $AnyEvent::MODEL @@ -370,12 +623,10 @@ The known classes so far are: - AnyEvent::Impl::CoroEV based on Coro::EV, best choice. - AnyEvent::Impl::CoroEvent based on Coro::Event, 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::Perl pure-perl implementation, inefficient but portable. AnyEvent::Impl::Tk based on Tk, very bad choice. AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. @@ -397,6 +648,25 @@ would have created an AnyEvent watcher anyway, that is, as late as possible at runtime. + $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 Coro::BDB for a case where this is useful. + + @AnyEvent::post_detect + If there are any code references in this array (you can "push" to it + before or after loading AnyEvent), then they will called directly + 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. + + Best use "AnyEvent::post_detect { BLOCK }" instead. + WHAT TO DO IN A MODULE As a module author, you should "use AnyEvent" and call AnyEvent methods freely, but you should not load a specific event module or rely on it. @@ -406,14 +676,14 @@ so by calling AnyEvent in your module body you force the user of your module to load the event module first. - Never call "->wait" on a condition variable unless you *know* that the - "->broadcast" 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. + Never call "->recv" on a condition variable unless you *know* that the + "->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 "->wait" when the user of your module + It is fine, however, to call "->recv" when the user of your module requests it (i.e. if you create a http request object ad have a method - called "results" that returns the results, it should call "->wait" + called "results" that returns the results, it should call "->recv" freely, as the user of your module knows what she is doing. always). WHAT TO DO IN THE MAIN PROGRAM @@ -425,8 +695,8 @@ 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 the Glib module. You should load the + 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 @@ -434,9 +704,25 @@ 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 "AnyEvent::Impl::Perl" module, which gives you similar - behaviour everywhere, but letting AnyEvent chose is generally better. + You can chose to use a pure-perl implementation by loading the + "AnyEvent::Impl::Perl" module, which gives you similar behaviour + everywhere, but letting AnyEvent chose the model is generally better. + + MAINLOOP EMULATION + Sometimes (often for short test scripts, or even standalone programs who + only want to use AnyEvent), you do not want to run a specific event + loop. + + In that case, you can use a condition variable like this: + + AnyEvent->condvar->recv; + + This has the effect of entering the event loop and looping forever. + + Note that usually your program has some exit condition, in which case it + is better to use the "traditional" approach of storing a condition + variable somewhere, waiting for it, and sending it when the program + should exit cleanly. OTHER MODULES The following is a non-exhaustive list of additional modules that use @@ -449,23 +735,50 @@ blocking functions such as "inet_aton" by event-/callback-based versions. + AnyEvent::Socket + Provides various utility functions for (internet protocol) sockets, + addresses and name resolution. Also functions to create non-blocking + tcp connections or tcp servers, with IPv6 and SRV record support and + more. + AnyEvent::Handle - Provide read and write buffers and manages watchers for reads and - writes. + Provide read and write buffers, manages watchers for reads and + writes, supports raw and formatted I/O, I/O queued and fully + transparent and non-blocking SSL/TLS. - AnyEvent::Socket - Provides a means to do non-blocking connects, accepts etc. + AnyEvent::DNS + Provides rich asynchronous DNS resolver capabilities. + + AnyEvent::HTTP + A simple-to-use HTTP library that is capable of making a lot of + concurrent HTTP requests. AnyEvent::HTTPD Provides a simple web application server framework. - AnyEvent::DNS - Provides asynchronous DNS resolver capabilities, beyond what - AnyEvent::Util offers. - AnyEvent::FastPing The fastest ping in the west. + AnyEvent::DBI + Executes DBI requests asynchronously in a proxy process. + + AnyEvent::AIO + Truly asynchronous I/O, should be in the toolbox of every event + programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent + together. + + AnyEvent::BDB + Truly asynchronous Berkeley DB access. AnyEvent::BDB transparently + fuses BDB and AnyEvent together. + + AnyEvent::GPSD + A non-blocking interface to gpsd, a daemon delivering GPS + information. + + AnyEvent::IGS + A non-blocking interface to the Internet Go Server protocol (used by + App::IGS). + Net::IRC3 AnyEvent based IRC client module family. @@ -480,18 +793,106 @@ High level API for event-based execution flow control. Coro - Has special support for AnyEvent. + Has special support for AnyEvent via Coro::AnyEvent. IO::Lambda The lambda approach to I/O - don't ask, look there. Can use AnyEvent. - IO::AIO - Truly asynchronous I/O, should be in the toolbox of every event - programmer. Can be trivially made to use AnyEvent. +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. - BDB Truly asynchronous Berkeley DB access. Can be trivially made to use - AnyEvent. +ENVIRONMENT VARIABLES + The following environment variables are used by this module or its + submodules: + + "PERL_ANYEVENT_VERBOSE" + By default, AnyEvent will be completely silent except in fatal + conditions. You can set this environment variable to make AnyEvent + more talkative. + + When set to 1 or higher, causes AnyEvent to warn about unexpected + conditions, such as not being able to load the event model specified + by "PERL_ANYEVENT_MODEL". + + When set to 2 or higher, cause AnyEvent to report to STDERR which + event model it chooses. + + "PERL_ANYEVENT_STRICT" + AnyEvent does not do much argument checking by default, as thorough + argument checking is very costly. Setting this variable to a true + value will cause AnyEvent to load "AnyEvent::Strict" and then to + thoroughly check the arguments passed to most method calls. If it + finds any problems it will croak. + + In other words, enables "strict" mode. + + Unlike "use strict", it is definitely recommended ot keep it off in + production. Keeping "PERL_ANYEVENT_STRICT=1" in your environment + while developing programs can be very useful, however. + + "PERL_ANYEVENT_MODEL" + This can be used to specify the event model to be used by AnyEvent, + before auto detection and -probing kicks in. It must be a string + consisting entirely of ASCII letters. The string "AnyEvent::Impl::" + 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 auto detection and -probing. + + This functionality might change in future versions. + + For example, to force the pure perl model (AnyEvent::Impl::Perl) you + could start your program like this: + + PERL_ANYEVENT_MODEL=Perl perl ... + + "PERL_ANYEVENT_PROTOCOLS" + Used by both AnyEvent::DNS and AnyEvent::Socket to determine + preferences for IPv4 or IPv6. The default is unspecified (and might + change, or be the result of auto probing). + + Must be set to a comma-separated list of protocols or address + families, current supported: "ipv4" and "ipv6". Only protocols + mentioned will be used, and preference will be given to protocols + mentioned earlier in the list. + + 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- + + Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over + IPv6, but support both and try to use both. + "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to + resolve or contact IPv6 addresses. + "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but + prefer IPv6 over IPv4. + + "PERL_ANYEVENT_EDNS0" + Used by AnyEvent::DNS to decide whether to use the EDNS0 extension + for DNS. This extension is generally useful to reduce DNS traffic, + but some (broken) firewalls drop such DNS packets, which is why it + is off by default. + + Setting this variable to 1 will cause AnyEvent::DNS to announce + EDNS0 in its DNS requests. + + "PERL_ANYEVENT_MAX_FORKS" + The maximum number of child processes that + "AnyEvent::Util::fork_call" will create in parallel. SUPPLYING YOUR OWN EVENT MODEL INTERFACE This is an advanced topic that you do not normally need to use AnyEvent @@ -536,36 +937,6 @@ "die". This still works with most modules/usages, and blocking calls must not be done in an interactive application, so it makes sense. -ENVIRONMENT VARIABLES - The following environment variables are used by this module: - - "PERL_ANYEVENT_VERBOSE" - 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 1 or higher, causes AnyEvent to warn about unexpected - conditions, such as not being able to load the event model specified - by "PERL_ANYEVENT_MODEL". - - When set to 2 or higher, cause AnyEvent to report to STDERR which - event model it chooses. - - "PERL_ANYEVENT_MODEL" - 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 "AnyEvent::Impl::" - 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 (AnyEvent::Impl::Perl) you - could start your program like this: - - PERL_ANYEVENT_MODEL=Perl perl ... - 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 @@ -582,7 +953,7 @@ 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 + $cv->send if $input =~ /^q/i; # quit program if /^q/i }, ); @@ -597,7 +968,7 @@ new_timer; # create first timer - $cv->wait; # wait until user enters /^q/i + $cv->recv; # wait until user enters /^q/i REAL-WORLD EXAMPLE Consider the Net::FCP module. It features (among others) the following @@ -656,13 +1027,13 @@ $txn->{w} = AnyEvent->io (fh => $txn->{fh}, poll => 'r', cb => sub { $txn->fh_ready_r }); Again, "fh_ready_r" waits till all data has arrived, and then stores the - result and signals any possible waiters that the request ahs finished: + result and signals any possible waiters that the request has finished: sysread $txn->{fh}, $txn->{buf}, length $txn->{$buf}; if (end-of-file or data complete) { $txn->{result} = $txn->{buf}; - $txn->{finished}->broadcast; + $txn->{finished}->send; $txb->{cb}->($txn) of $txn->{cb}; # also call callback } @@ -670,11 +1041,11 @@ request was already finished, it doesn't wait, of course, and returns the data: - $txn->{finished}->wait; + $txn->{finished}->recv; return $txn->{result}; The actual code goes further and collects all errors ("die"s, - exceptions) that occured during request processing. The "result" method + exceptions) that occurred during request processing. The "result" method detects 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, @@ -715,10 +1086,10 @@ $fcp->txn_client_get ($url)->cb (sub { ... - $quit->broadcast; + $quit->send; }); - $quit->wait; + $quit->recv; BENCHMARKS To give you an idea of the performance and overheads that AnyEvent adds @@ -727,7 +1098,7 @@ 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 + 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. @@ -753,8 +1124,8 @@ *invoke* 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 "->broadcast" a condvar once to signal the end - of this phase. + "watcher" times, it would "->send" a condvar once to signal the end of + this phase. *destroy* is the time, in microseconds, that it takes to destroy a single watcher. @@ -825,14 +1196,19 @@ "POE", 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: 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 this, as session creation overhead is small compared - to execution of the state machine, which is coded pretty optimally - within AnyEvent::Impl::POE. POE simply seems to be abysmally slow. + 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 AnyEvent::Impl::POE (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). Summary * Using EV through AnyEvent is faster than any other event loop (even @@ -847,8 +1223,8 @@ reasonable memory usage. 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 + This benchmark actually benchmarks the event loop itself. It works by + creating a number of "servers": each server consists of a socket pair, 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 @@ -856,11 +1232,11 @@ 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). + active fds for each loop iteration, 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 + In this benchmark, we use 10000 socket pairs (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. @@ -871,7 +1247,7 @@ *sockets* is the number of sockets, and twice the number of "servers" (as each server has a read and write socket end). - *create* is the time it takes to create a socketpair (which is + *create* is the time it takes to create a socket pair (which is nontrivial) and two watchers: an I/O watcher and a timeout watcher. *request*, the most important value, is the time it takes to handle a @@ -911,8 +1287,7 @@ though it uses a C-based event loop in this case. Summary - * The pure perl implementation performs extremely well, considering - that it uses select. + * The pure perl implementation performs extremely well. * Avoid Glib or POE in large projects where performance matters. @@ -946,7 +1321,7 @@ EV is again fastest. - Perl again comes second. It is noticably faster than the C-based event + Perl again comes second. It is noticeably faster than the C-based event loops Event and Glib, although the difference is too small to really matter. @@ -959,7 +1334,8 @@ FORK Most event libraries are not fork-safe. The ones who are usually are - because they are so inefficient. Only EV is fully fork-aware. + 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. @@ -975,22 +1351,42 @@ You can make AnyEvent completely ignore this variable by deleting it before the first watcher gets created, e.g. with a "BEGIN" block: - BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } - - use AnyEvent; + BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } + + 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}. + +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 + not as pronounced). SEE ALSO - Event modules: Coro::EV, EV, EV::Glib, Glib::EV, Coro::Event, Event, - Glib::Event, Glib, Coro, Tk, Event::Lib, Qt, POE. + Utility functions: AnyEvent::Util. + + Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, + Event::Lib, Qt, POE. + + 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. + + Non-blocking file handles, sockets, TCP clients and servers: + AnyEvent::Handle, AnyEvent::Socket. + + Asynchronous DNS: AnyEvent::DNS. - Implementations: AnyEvent::Impl::CoroEV, AnyEvent::Impl::EV, - AnyEvent::Impl::CoroEvent, AnyEvent::Impl::Event, AnyEvent::Impl::Glib, - AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, AnyEvent::Impl::EventLib, - AnyEvent::Impl::Qt, AnyEvent::Impl::POE. + Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, - Nontrivial usage examples: Net::FCP, Net::XMPP2. + Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS. AUTHOR - Marc Lehmann - http://home.schmorp.de/ + Marc Lehmann + http://home.schmorp.de/