AnyEvent(3) User Contributed Perl Documentation AnyEvent(3)NAMECoro::AnyEvent - integrate threads into AnyEvent
SYNOPSIS
use Coro;
use AnyEvent;
# using both Coro and AnyEvent will automatically load Coro::AnyEvent
# or load it manually for it's utility functions:
use Coro::AnyEvent;
Coro::AnyEvent::sleep 5; # block current thread for 5s
Coro::AnyEvent::poll; # poll for new events once
Coro::AnyEvent::idle; # block until process no longer busy
Coro::AnyEvent::idle_upto 5; # same, but only up to 5 seconds
Coro::AnyEvent::readable $fh, 60
or die "fh didn't become readable within 60 seconds\n";
DESCRIPTION
When one naively starts to use threads in Perl, one will quickly run
into the problem that threads that block on a syscall (sleeping,
reading from a socket etc.) will block all threads.
If one then uses an event loop, the problem is that the event loop has
no knowledge of threads and will not run them before it polls for new
events, again blocking the whole process.
This module integrates threads into any event loop supported by
AnyEvent, combining event-based programming with coroutine-based
programming in a natural way.
As of Coro 5.21 and newer, this module gets loaded automatically when
AnyEvent initialises itself and Coro is used in the same process, thus
there is no need to load it manually if you just want your threads to
coexist with AnyEvent.
If you want to use any functions from this module, you of course still
need to "use Coro::AnyEvent", just as with other perl modules.
Also, this module autodetects the event loop used (by relying on
AnyEvent) and will either automatically defer to the high-performance
Coro::EV or Coro::Event modules, or will use a generic integration
method that should work with any event loop supported by AnyEvent.
USAGE
RUN AN EVENT LOOP - OR NOT?
For performance reasons, it is recommended that the main program or
something else runs the event loop of the event model you use, i.e.
use Gtk2; # <- the event model
use AnyEvent;
use Coro:
# initialise stuff
async { ... };
# now run mainloop of Gtk2
main Gtk2;
You can move the event loop into a thread as well, although this tends
to get confusing:
use Gtk2;
use AnyEvent;
use Coro:
async { main Gtk2 };
# do other things...
while () {
use Coro::AnyEvent;
Coro::AnyEvent::sleep 1;
print "ping...\n";
}
You can also do nothing, in which case Coro:AnyEvent will invoke the
event loop as needed, which is less efficient, but sometimes very
convenient.
What you MUST NOT DO EVER is to block inside an event loop callback.
The reason is that most event loops are not reentrant and this can
cause a deadlock at best and corrupt memory at worst.
Coro will try to catch you when you block in the event loop
("FATAL:$Coro::IDLE blocked itself"), but this is just best effort and
only works when you do not run your own event loop.
To avoid this problem, simply do not block inside an event callback -
start a new thread (e.g. with "Coro:async_pool") or use
"Coro::unblock_sub".
INVERSION OF CONTROL
If you need to wait for a single event, the rouse functions will come
in handy (see the Coro manpage for details):
# wait for single SIGINT
{
my $int_w = AnyEvent->signal (signal => "INT", cb => Coro::rouse_cb);
Coro::rouse_wait;
}
EVENT MODULES OTHER THEN ANYEVENT
Keep in mind that, as shipped, Coro and Coro::AnyEvent only work with
AnyEvent, and only when AnyEvent is actually used (i.e. initialised),
so this will not work:
# does not work: EV without AnyEvent is not recognised
use EV;
use Coro;
EV::loop;
And neither does this, unless you actually use AnyEvent for something:
# does not work: AnyEvent must be initialised (e.g. by creating watchers)
use EV;
use AnyEvent;
use Coro;
EV::loop;
This does work, however, because you create a watcher (condvars work,
too), thus forcing AnyEvent to initialise itself:
# does work: AnyEvent is actually used
use EV;
use AnyEvent;
use Coro;
my $timer = AE::timer 1, 1, sub { };
EV::loop;
And if you want to use AnyEvent just to bridge between Coro and your
event model of choice, you can simply force it to initialise itself,
like this:
# does work: AnyEvent is initialised manually
use POE;
use AnyEvent;
use Coro;
AnyEvent::detect; # force AnyEvent to integrate Coro into POE
POE::Kernel->run;
FUNCTIONSCoro::AnyEvent also offers a few functions that might be useful.
Coro::AnyEvent::poll
This call will block the current thread until the event loop has
polled for potential new events and instructs the event loop to
poll for new events once, without blocking.
Note that this call will not actually execute the poll, nor will it
wait until there are some events, just block until the event loop
has polled for new events, so other threads will have a chance to
run.
This is useful when you have a thread that does some computations,
but you still want to poll for new events from time to time. Simply
call "poll" from time to time:
my $long_calc = async {
for (1..10000) {
Coro::AnyEvent::poll:
# do some stuff, make sure it takes at least 0.001s or so
}
}
Although you should also consider "idle" or "idle_upto" in such
cases.
Coro::AnyEvent::sleep $seconds
This blocks the current thread for at least the given number of
seconds.
Coro::AnyEvent::idle
This call is similar to "poll" in that it will also poll for
events. Unlike "poll", it will only resume the thread once there
are no events to handle anymore, i.e. when the process is otherwise
idle.
This is good for background threads that shouldn't use CPU time
when foreground jobs are ready to run.
Coro::AnyEvent::idle_upto $seconds
Like "idle", but with a maximum waiting time.
If your process is busy handling events, calling "idle" can mean
that your thread will never be resumed. To avoid this, you can use
"idle_upto" and specify a timeout, after which your thread will be
resumed even if the process is completely busy.
Coro::AnyEvent::readable $fh_or_fileno[, $timeout]
Coro::AnyEvent::writable $fh_or_fileno[, $timeout]
Blocks the current thread until the given file handle (or file
descriptor) becomes readable (or writable), or the given timeout
has elapsed, whichever happens first. No timeout counts as infinite
timeout.
Returns true when the file handle became ready, false when a
timeout occured.
Note that these functions are quite inefficient as compared to
using a single watcher (they recreate watchers on every invocation)
or compared to using Coro::Handle.
Note also that they only work for sources that have reasonable non-
blocking behaviour (e.g. not files).
Example: wait until STDIN becomes readable, then quit the program.
use Coro::AnyEvent;
print "press enter to quit...\n";
Coro::AnyEvent::readable *STDIN;
exit 0;
IMPLEMENTATION DETAILS
Unfortunately, few event loops (basically only EV and Event) support
the kind of integration required for smooth operations well, and
consequently, AnyEvent cannot completely offer the functionality
required by this module, so we need to improvise.
Here is what this module does when it has to work with other event
loops:
· run ready threads before blocking the process
Each time a thread is put into the ready queue (and there are no
other threads in the ready queue), a timer with an "after" value of
0 is registered with AnyEvent.
This creates something similar to an idle watcher, i.e. a watcher
that keeps the event loop from blocking but still polls for new
events. (Unfortunately, some badly designed event loops (e.g.
Event::Lib) don't support a timeout of 0 and will always block for
a bit).
The callback for that timer will "cede" to other threads of the
same or higher priority for as long as such threads exists. This
has the effect of running all threads that have work to do until
all threads block to wait for external events.
If no threads of equal or higher priority are ready, it will cede
to any thread, but only once. This has the effect of running lower-
priority threads as well, but it will not keep higher priority
threads from receiving new events.
The priority used is simply the priority of the thread that runs
the event loop, usually the main program, which usually has a
priority of 0. Note that Coro::AnyEvent does not run an event loop
for you, so unless the main program runs one, there will simply be
no event loop to "cede" to (event handling will still work,
somewhat inefficiently, but any thread will have a higher priority
than event handling in that case).
· provide a suitable idle callback.
In addition to hooking into "ready", this module will also provide
a $Coro::idle handler that runs the event loop. It is best not to
take advantage of this too often, as this is rather inefficient,
but it should work perfectly fine.
· provide overrides for AnyEvent's condvars
This module installs overrides for AnyEvent's condvars. That is,
when the module is loaded it will provide its own condition
variables. This makes them coroutine-safe, i.e. you can safely
block on them from within a coroutine.
· lead to data corruption or worse
As "unblock_sub" cannot be used by this module (as it is the module
that implements it, basically), you must not call into the event
loop recursively from any coroutine. This is not usually a
difficult restriction to live with, just use condvars,
"unblock_sub" or other means of inter-coroutine-communications.
If you use a module that supports AnyEvent (or uses the same event
loop as AnyEvent, making the compatible), and it offers callbacks
of any kind, then you must not block in them, either (or use e.g.
"unblock_sub"), see the description of "unblock_sub" in the Coro
module.
This also means that you should load the module as early as
possible, as only condvars created after this module has been
loaded will work correctly.
SEE ALSO
AnyEvent, to see which event loops are supported, Coro::EV and
Coro::Event for more efficient and more correct solutions (they will be
used automatically if applicable).
AUTHOR
Marc Lehmann <schmorp@schmorp.de>
http://home.schmorp.de/
perl v5.14.2 2011-11-11 AnyEvent(3)