--- AnyEvent/README 2008/05/10 22:30:28 1.20 +++ AnyEvent/README 2008/06/22 12:17:47 1.27 @@ -19,6 +19,11 @@ $w->send; # wake up current and all future recv's $w->recv; # enters "main loop" till $condvar gets ->send +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 nowadays. So what is different about AnyEvent? @@ -48,7 +53,7 @@ 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 @@ -57,12 +62,18 @@ 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. @@ -101,12 +112,12 @@ 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 +135,10 @@ 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 @@ -222,6 +233,68 @@ 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 @@ -231,10 +304,10 @@ 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. @@ -271,21 +344,21 @@ Example: fork a process and wait for it - 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 $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; CONDITION VARIABLES If you are familiar with some event loops you will know that all of them @@ -303,14 +376,16 @@ "cb", 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 "send" method. + 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 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 + 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 @@ -325,7 +400,7 @@ button of your app, which would "->send" the "quit" event. Note that condition variables recurse into the event loop - if you have - two pieces of code that call "->recv" 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. @@ -340,7 +415,7 @@ which eventually calls "-> send", and the "consumer side", which waits for the send to occur. - Example: + Example: wait for a timer. # wait till the result is ready my $result_ready = AnyEvent->condvar; @@ -358,6 +433,13 @@ # calls send $result_ready->recv; + Example: wait for a timer, but take advantage of the fact that condition + variables are also code references. + + my $done = AnyEvent->condvar; + my $delay = AnyEvent->timer (after => 5, cb => $done); + $done->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 @@ -375,6 +457,15 @@ 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. @@ -429,7 +520,7 @@ 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 eahc subrequest you finish, call + you start, call "begin" and for each subrequest you finish, call "end". METHODS FOR CONSUMERS @@ -455,7 +546,7 @@ 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 "->recv" in a module is that you cannot @@ -483,8 +574,9 @@ optionally replaces it before doing so. The callback will be called when the condition becomes "true", i.e. - when "send" or "croak" are called. Calling "recv" inside the - callback or at any later time is guaranteed not to block. + 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 @@ -568,8 +660,8 @@ 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 @@ -577,9 +669,25 @@ 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 @@ -596,16 +704,28 @@ Provide read and write buffers and manages watchers for reads and writes. - AnyEvent::HTTPD - Provides a simple web application server framework. + 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::DNS - Provides asynchronous DNS resolver capabilities, beyond what - AnyEvent::Util offers. + 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::FastPing The fastest ping in the west. + AnyEvent::DBI + Executes DBI requests asynchronously in a proxy process. + Net::IRC3 AnyEvent based IRC client module family. @@ -695,18 +815,53 @@ "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 + 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 autodetection and -probing. + 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_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. EXAMPLE PROGRAM The following program uses an I/O watcher to read data from STDIN, a @@ -724,7 +879,7 @@ 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 }, ); @@ -739,7 +894,7 @@ 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 @@ -798,13 +953,13 @@ $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 } @@ -812,11 +967,11 @@ 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, @@ -857,10 +1012,10 @@ $fcp->txn_client_get ($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 @@ -869,7 +1024,7 @@ 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. @@ -895,8 +1050,8 @@ *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. @@ -994,8 +1149,8 @@ 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 @@ -1003,11 +1158,11 @@ 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. @@ -1018,7 +1173,7 @@ *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 @@ -1092,7 +1247,7 @@ 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. @@ -1122,15 +1277,24 @@ 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). +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 + Utility functions: AnyEvent::Util. + Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, Event::Lib, Qt, POE. @@ -1138,11 +1302,16 @@ 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. + 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/