--- AnyEvent/lib/AnyEvent.pm 2007/11/02 19:12:02 1.30 +++ AnyEvent/lib/AnyEvent.pm 2008/04/25 06:58:12 1.65 @@ -2,7 +2,7 @@ AnyEvent - provide framework for multiple event loops -Event, Coro, Glib, Tk, Perl - various supported event loops +EV, Event, Coro::EV, Coro::Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event loops =head1 SYNOPSIS @@ -16,10 +16,59 @@ ... }); - my $w = AnyEvent->condvar; # stores wether a condition was flagged + 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 +=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 L provides an identical interface to multiple event loops. This @@ -27,19 +76,22 @@ 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, L, +L. The first one found is used. If none are found, the module tries +to load these modules (excluding 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 +99,10 @@ # .. 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 +114,50 @@ 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 +Many watchers either are used with "recursion" (repeating timers for +example), or need to refer to their watcher object in other ways. -You can create I/O watcher by calling the C<< AnyEvent->io >> method with -the following mandatory arguments: +An any way to achieve that is this pattern: -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 teh 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). + 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. -Filehandles will be kept alive, so as long as the watcher exists, the -filehandle exists, too. +=head2 IO 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. + +As long as the I/O watcher exists it will keep the file descriptor or a +copy of it alive/open. + +It is not allowed to 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 +173,9 @@ 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) should the timer activate. C the callback to invoke in that +case. 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 @@ -111,17 +189,107 @@ }); # to cancel the timer: - undef $w + undef $w; + +Example 2: + + # fire an event after 0.5 seconds, then roughly every second + my $w; + + my $cb = sub { + # cancel the old timer while creating a new one + $w = AnyEvent->timer (after => 1, cb => $cb); + }; + + # start the "loop" by creating the first watcher + $w = AnyEvent->timer (after => 0.5, cb => $cb); + +=head3 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 +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. + +AnyEvent always prefers relative timers, if available, matching the +AnyEvent API. + +=head2 SIGNAL WATCHERS + +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. + +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. + +The main advantage of using these watchers is that you can share a signal +between multiple watchers. + +This watcher might use C<%SIG>, so programs overwriting those signals +directly will likely not work correctly. + +Example: exit on SIGINT + + my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); + +=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). + +Example: wait for pid 1333 + + my $w = AnyEvent->child ( + pid => 1333, + cb => sub { + my ($pid, $status) = @_; + warn "pid $pid exited with status $status"; + }, + ); -=head2 CONDITION WATCHERS +=head2 CONDITION VARIABLES -Condition watchers can be created by calling the C<< AnyEvent->condvar >> +Condition variables can be created by calling the C<< AnyEvent->condvar >> method without any arguments. -A condition watcher watches for a condition - precisely that the C<< +A condition variable waits for a condition - precisely that the C<< ->broadcast >> method has been called. -The watcher has only two methods: +They are very useful to signal that a condition has been fulfilled, for +example, if you write a module that does asynchronous http requests, +then a condition variable would be the ideal candidate to signal the +availability of results. + +You can also use condition variables to block your main program until +an event occurs - for example, you could C<< ->wait >> in your main +program until the user clicks the Quit button in your app, which would C<< +->broadcast >> the "quit" event. + +Note that condition variables recurse into the event loop - if you have +two pirces of code that call C<< ->wait >> in a round-robbin fashion, you +lose. Therefore, condition variables are good to export to your caller, but +you should avoid making a blocking wait yourself, at least in callbacks, +as this asks for trouble. + +This object has two methods: =over 4 @@ -130,21 +298,31 @@ Wait (blocking if necessary) until the C<< ->broadcast >> method has been called on c<$cv>, while servicing other watchers normally. -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 only wait once on a condition - additional calls will return immediately. +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 coroutine-aware backends L and +L explicitly support concurrent C<< ->wait >>'s +from different coroutines, however). + =item $cv->broadcast 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.. +calls to C will (eventually) return after this method has been +called. If nobody is waiting the broadcast will be remembered.. + +=back Example: @@ -154,36 +332,17 @@ # 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; -=back - -=head2 SIGNAL WATCHERS - -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. - -These watchers might use C<%SIG>, so programs overwriting those signals -directly will likely not work correctly. - -Example: exit on SIGINT - - my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); - -=head2 CHILD PROCESS WATCHERS - -You can also listen for the status of a child process specified by the -C argument. The watcher will only trigger once. This works by -installing a signal handler for C. - -Example: wait for pid 1333 - - my $w = AnyEvent->child (pid => 1333, cb => sub { warn "exit status $?" }); - -=head1 GLOBALS +=head1 GLOBAL VARIABLES AND FUNCTIONS =over 4 @@ -197,50 +356,76 @@ The known classes so far are: - EV::AnyEvent based on EV (an interface to libev, best choice) - AnyEvent::Impl::Coro based on Coro::Event, second best choice. - AnyEvent::Impl::Event based on Event, also second best choice :) - AnyEvent::Impl::Glib based on Glib, second-best choice. + AnyEvent::Impl::CoroEV based on Coro::EV, best choice. + AnyEvent::Impl::CoroEvent based on Coro::Event, second best choice. + AnyEvent::Impl::EV based on EV (an interface to libev, best choice). + AnyEvent::Impl::Event based on Event, second best choice. + AnyEvent::Impl::Glib based on Glib, third-best choice. AnyEvent::Impl::Tk based on Tk, very bad choice. - AnyEvent::Impl::Perl pure-perl implementation, inefficient. + AnyEvent::Impl::Perl pure-perl implementation, inefficient but portable. + AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs). + AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse. + AnyEvent::Impl::POE based on POE, not generic enough for full support. + +There is no support for WxWidgets, as WxWidgets has no support for +watching file handles. However, you can use WxWidgets through the +POE Adaptor, as POE has a Wx backend that simply polls 20 times per +second, which was considered to be too horrible to even consider for +AnyEvent. Likewise, other POE backends can be used by AnyEvent by using +it's adaptor. + +AnyEvent knows about L and L and will try to use L when +autodetecting them. =item AnyEvent::detect -Returns C<$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. =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<< ->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. + +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. =cut @@ -251,7 +436,7 @@ use Carp; -our $VERSION = '2.55'; +our $VERSION = '3.3'; our $MODEL; our $AUTOLOAD; @@ -262,48 +447,67 @@ our @REGISTRY; my @models = ( - [Coro::Event:: => AnyEvent::Impl::Coro::], - [EV:: => EV::AnyEvent::], + [Coro::EV:: => AnyEvent::Impl::CoroEV::], + [Coro::Event:: => AnyEvent::Impl::CoroEvent::], + [EV:: => AnyEvent::Impl::EV::], [Event:: => AnyEvent::Impl::Event::], [Glib:: => AnyEvent::Impl::Glib::], [Tk:: => AnyEvent::Impl::Tk::], + [Wx:: => AnyEvent::Impl::POE::], + [Prima:: => AnyEvent::Impl::POE::], [AnyEvent::Impl::Perl:: => AnyEvent::Impl::Perl::], + # everything below here will not be autoprobed as the pureperl backend should work everywhere + [Event::Lib:: => AnyEvent::Impl::EventLib::], # too buggy + [Qt:: => AnyEvent::Impl::Qt::], # requires special main program + [POE::Kernel:: => AnyEvent::Impl::POE::], # lasciate ogni speranza ); -our %method = map +($_ => 1), qw(io timer condvar broadcast wait signal one_event DESTROY); +our %method = map +($_ => 1), qw(io timer signal child condvar broadcast wait one_event DESTROY); sub detect() { unless ($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; + } } } - $MODEL - or die "No event module selected for AnyEvent and autodetect failed. Install any one of these modules: Event (or Coro+Event), Glib or Tk."; + unless ($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 (or Coro+EV), Event (or Coro+Event) or Glib."; + } } unshift @ISA, $MODEL; @@ -351,7 +555,7 @@ my $signal = uc $arg{signal} or Carp::croak "required option 'signal' is missing"; - $SIG_CB{$signal}{$arg{cb} += 0} = $arg{cb}; + $SIG_CB{$signal}{$arg{cb}} = $arg{cb}; $SIG{$signal} ||= sub { $_->() for values %{ $SIG_CB{$signal} || {} }; }; @@ -371,21 +575,31 @@ our %PID_CB; our $CHLD_W; +our $CHLD_DELAY_W; our $PID_IDLE; our $WNOHANG; sub _child_wait { while (0 < (my $pid = waitpid -1, $WNOHANG)) { - $_->() for values %{ $PID_CB{$pid} || {} }, %{ $PID_CB{0} || {} }; + $_->($pid, $?) for (values %{ $PID_CB{$pid} || {} }), + (values %{ $PID_CB{0} || {} }); } undef $PID_IDLE; } +sub _sigchld { + # make sure we deliver these changes "synchronous" with the event loop. + $CHLD_DELAY_W ||= AnyEvent->timer (after => 0, cb => sub { + undef $CHLD_DELAY_W; + &_child_wait; + }); +} + sub child { my (undef, %arg) = @_; - my $pid = uc $arg{pid} + defined (my $pid = $arg{pid} + 0) or Carp::croak "required option 'pid' is missing"; $PID_CB{$pid}{$arg{cb}} = $arg{cb}; @@ -395,9 +609,9 @@ } unless ($CHLD_W) { - $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_child_wait); - # child could be a zombie already - $PID_IDLE ||= AnyEvent->timer (after => 0, cb => \&_child_wait); + $CHLD_W = AnyEvent->signal (signal => 'CHLD', cb => \&_sigchld); + # child could be a zombie already, so make at least one round + &_sigchld; } bless [$pid, $arg{cb}], "AnyEvent::Base::Child" @@ -414,61 +628,104 @@ =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 -=head1 EXAMPLE +=item C -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: +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: + + PERL_ANYEVENT_MODEL=Perl perl ... + +=back + +=head1 EXAMPLE PROGRAM + +The following program uses an IO 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 @@ -560,7 +817,7 @@ 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. @@ -571,7 +828,7 @@ my $data = $fcp->client_get ($url); -2. Blocking, but parallelizing: +2. Blocking, but running in parallel: my @datas = map $_->result, map $fcp->txn_client_get ($_), @@ -580,9 +837,9 @@ 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; @@ -590,7 +847,7 @@ ... }); - Event::loop; + EV::loop; 3b. The module user could use AnyEvent, too: @@ -605,15 +862,124 @@ $quit->wait; + +=head1 BENCHMARK + +To give you an idea of the performance and overheads that AnyEvent adds +over the backends directly, here is a benchmark of various supported event +models natively and with anyevent. The benchmark creates a lot of timers +(with a zero timeout) and io events (watching STDOUT, a pty, to become +writable), lets them fire exactly once and destroys them again. + +Explanation of the fields: + +I is the number of event watchers created/destroyed. Sicne +different event models have vastly different performance each backend was +handed a number of watchers so that overall runtime is acceptable and +similar to all backends (and keep them from crashing). + +I is the number of bytes (as measured by resident set size) used by +each watcher. + +I is the time, in microseconds, to create a single watcher. + +I is the time, in microseconds, used to invoke a simple callback +that simply counts down. + +I is the time, in microseconds, to destroy a single watcher. + + name watcher bytes create invoke destroy comment + EV/EV 400000 244 0.56 0.46 0.31 EV native interface + EV/Any 100000 610 3.52 0.91 0.75 + CoroEV/Any 100000 610 3.49 0.92 0.75 coroutines + Coro::Signal + Perl/Any 10000 654 4.64 1.22 0.77 pure perl implementation + Event/Event 10000 523 28.05 21.38 5.22 Event native interface + Event/Any 10000 943 34.43 20.48 1.39 + Glib/Any 16000 1357 96.99 12.55 55.51 quadratic behaviour + Tk/Any 2000 1855 27.01 66.61 14.03 SEGV with >> 2000 watchers + POE/Select 2000 6343 94.69 807.65 562.69 POE::Loop::Select + POE/Event 2000 6644 108.15 768.19 14.33 POE::Loop::Event + +Discussion: The benchmark does I bench scalability of the +backend. For example a select-based backend (such as the pureperl one) can +never compete with a backend using epoll. In this benchmark, only a single +filehandle is used. + +EV is the sole leader regarding speed and memory use, which are both +maximal/minimal. Even when going through AnyEvent, there is only one event +loop that uses less memory (the Event module natively), and no faster +event model. + +The pure perl implementation is hit in a few sweet spots (both the +zero timeout and the use of a single fd hit optimisations in the perl +interpreter and the backend itself), but it shows that it adds very little +overhead in itself. Like any select-based backend it's performance becomes +really bad with lots of file descriptors. + +The Event module has a relatively high setup and callback invocation cost, +but overall scores on the third place. + +Glib has a little higher memory cost, a bit fster callback invocation and +has a similar speed as Event. + +The Tk backend works relatively well, the fact that it crashes with +more than 2000 watchers is a big setback, however, as correctness takes +precedence over speed. + +POE, regardless of backend (wether it's pure perl select backend or the +Event backend) shows abysmal performance and memory usage: Watchers use +almost 30 times as much memory as EV watchers, and 10 times as much memory +as both Event or EV via AnyEvent. + +Summary: using EV through AnyEvent is faster than any other event +loop. The overhead AnyEvent adds can be very small, and you should avoid +POE like the plague if you want performance or reasonable memory usage. + + +=head1 FORK + +Most event libraries are not fork-safe. The ones who are usually are +because they are so inefficient. Only L is fully fork-aware. + +If you have to fork, you must either do so I creating your first +watcher OR you must not use AnyEvent at all in the child. + + +=head1 SECURITY CONSIDERATIONS + +AnyEvent can be forced to load any event model via +$ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used to +execute arbitrary code or directly gain access, it can easily be used to +make the program hang or malfunction in subtle ways, as AnyEvent watchers +will not be active when the program uses a different event model than +specified in the variable. + +You can make AnyEvent completely ignore this variable by deleting it +before the first watcher gets created, e.g. with a C block: + + BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } + + use AnyEvent; + + =head1 SEE ALSO -Event modules: L, L, L, L, L. +Event modules: L, L, L, L, +L, L, L, L, L, L, +L, L, L. + +Implementations: L, L, +L, L, L, +L, L, L, +L, L. + +Nontrivial usage examples: L, L. -Implementations: L, L, L, L. -Nontrivial usage example: L. +=head1 AUTHOR -=head1 + Marc Lehmann + http://home.schmorp.de/ =cut