--- AnyEvent/README 2009/12/20 22:49:52 1.58 +++ AnyEvent/README 2010/04/28 14:15:55 1.61 @@ -7,7 +7,10 @@ SYNOPSIS use AnyEvent; - # file descriptor readable + # if you prefer function calls, look at the L manpage for + # an alternative API. + + # file handle or descriptor readable my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... }); # one-shot or repeating timers @@ -470,10 +473,10 @@ Example: fork a process and wait for it my $done = AnyEvent->condvar; - - my $pid = fork or exit 5; - - my $w = AnyEvent->child ( + + my $pid = fork or exit 5; + + my $w = AnyEvent->child ( pid => $pid, cb => sub { my ($pid, $status) = @_; @@ -481,25 +484,28 @@ $done->send; }, ); - - # do something else, then wait for process exit + + # do something else, then wait for process exit $done->recv; IDLE WATCHERS $w = AnyEvent->idle (cb => ); - Sometimes there is a need to do something, but it is not so important to - do it instantly, but only when there is nothing better to do. This - "nothing better to do" is usually defined to be "no other events need - attention by the event loop". - - Idle watchers ideally get invoked when the event loop has nothing better - to do, just before it would block the process to wait for new events. - Instead of blocking, the idle watcher is invoked. - - Most event loops unfortunately do not really support idle watchers (only - EV, Event and Glib do it in a usable fashion) - for the rest, AnyEvent - will simply call the callback "from time to time". + Repeatedly invoke the callback after the process becomes idle, until + either the watcher is destroyed or new events have been detected. + + Idle watchers are useful when there is a need to do something, but it is + not so important (or wise) to do it instantly. The callback will be + invoked only when there is "nothing better to do", which is usually + defined as "all outstanding events have been handled and no new events + have been detected". That means that idle watchers ideally get invoked + when the event loop has just polled for new events but none have been + detected. Instead of blocking to wait for more events, the idle watchers + will be invoked. + + Unfortunately, most event loops do not really support idle watchers + (only EV, Event and Glib do it in a usable fashion) - for the rest, + AnyEvent will simply call the callback "from time to time". Example: read lines from STDIN, but only process them when the program is otherwise idle: @@ -588,21 +594,21 @@ Example: wait for a timer. - # wait till the result is ready - my $result_ready = AnyEvent->condvar; + # condition: "wait till the timer is fired" + my $timer_fired = AnyEvent->condvar; - # do something such as adding a timer - # or socket watcher the calls $result_ready->send - # when the "result" is ready. + # create the timer - we could wait for, say + # a handle becomign ready, or even an + # AnyEvent::HTTP request to finish, but # in this case, we simply use a timer: my $w = AnyEvent->timer ( after => 1, - cb => sub { $result_ready->send }, + cb => sub { $timer_fired->send }, ); # this "blocks" (while handling events) till the callback # calls ->send - $result_ready->recv; + $timer_fired->recv; Example: wait for a timer, but take advantage of the fact that condition variables are also callable directly. @@ -1075,7 +1081,7 @@ SIMPLIFIED AE API Starting with version 5.0, AnyEvent officially supports a second, much simpler, API that is designed to reduce the calling, typing and memory - overhead. + overhead by using function call syntax and a fixed number of parameters. See the AE manpage for details. @@ -1350,7 +1356,7 @@ 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, + other problems get reported to the code that tries to use the result, not in a random callback. All of this enables the following usage styles: @@ -1773,6 +1779,9 @@ You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and Glib::EV). + If you only use backends that rely on another event loop (e.g. + "Tk"), then this module will do nothing for you. + Guard The guard module, when used, will be used to implement "AnyEvent::Util::guard". This speeds up guards considerably (and @@ -1781,12 +1790,9 @@ JSON and JSON::XS One of these modules is required when you want to read or write JSON - data via AnyEvent::Handle. It is also written in pure-perl, but can - take advantage of the ultra-high-speed JSON::XS module when it is - installed. - - In fact, AnyEvent::Handle will use JSON::XS by default if it is - installed. + data via AnyEvent::Handle. JSON is also written in pure-perl, but + can take advantage of the ultra-high-speed JSON::XS module when it + is installed. Net::SSLeay Implementing TLS/SSL in Perl is certainly interesting, but not very @@ -1802,12 +1808,17 @@ FORK Most event libraries are not fork-safe. The ones who are usually are - because they rely on inefficient but fork-safe "select" or "poll" calls. - Only EV is fully fork-aware. + because they rely on inefficient but fork-safe "select" or "poll" calls + - higher performance APIs such as BSD's kqueue or the dreaded Linux + epoll are usually badly thought-out hacks that are incompatible with + fork in one way or another. Only EV is fully fork-aware and ensures that + you continue event-processing in both parent and child (or both, if you + know what you are doing). This means that, in general, you cannot fork and do event processing in - the child if a watcher was created before the fork (which in turn - initialises the event library). + the child if the event library was initialised before the fork (which + usually happens when the first AnyEvent watcher is created, or the + library is loaded). 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 OR you must do @@ -1817,7 +1828,10 @@ much more complicated: even for backends that *are* fork-aware or fork-safe, their behaviour is not usually what you want: fork clones all watchers, that means all timers, I/O watchers etc. are active in both - parent and child, which is almost never what you want. + parent and child, which is almost never what you want. USing "exec" to + start worker children from some kind of manage rprocess is usually + preferred, because it is much easier and cleaner, at the expense of + having to have another binary. SECURITY CONSIDERATIONS AnyEvent can be forced to load any event model via @@ -1831,8 +1845,8 @@ before the first watcher gets created, e.g. with a "BEGIN" block: BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } - - use AnyEvent; + + use AnyEvent; Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can be used to probe what backend is used and gain other information (which