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1.1 |
NAME |
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1.19 |
Coro - the only real threads in perl |
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1.1 |
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SYNOPSIS |
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1.14 |
use Coro; |
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async { |
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# some asynchronous thread of execution |
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print "2\n"; |
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cede; # yield back to main |
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print "4\n"; |
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}; |
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print "1\n"; |
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cede; # yield to coroutine |
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print "3\n"; |
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cede; # and again |
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# use locking |
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use Coro::Semaphore; |
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my $lock = new Coro::Semaphore; |
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my $locked; |
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$lock->down; |
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$locked = 1; |
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$lock->up; |
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1.1 |
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DESCRIPTION |
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For a tutorial-style introduction, please read the Coro::Intro manpage. |
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This manpage mainly contains reference information. |
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1.1 |
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This module collection manages continuations in general, most often in |
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the form of cooperative threads (also called coroutines in the |
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documentation). They are similar to kernel threads but don't (in |
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general) run in parallel at the same time even on SMP machines. The |
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specific flavor of thread offered by this module also guarantees you |
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that it will not switch between threads unless necessary, at |
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easily-identified points in your program, so locking and parallel access |
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are rarely an issue, making thread programming much safer and easier |
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than using other thread models. |
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Unlike the so-called "Perl threads" (which are not actually real threads |
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but only the windows process emulation ported to unix), Coro provides a |
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full shared address space, which makes communication between threads |
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very easy. And threads are fast, too: disabling the Windows process |
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emulation code in your perl and using Coro can easily result in a two to |
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four times speed increase for your programs. |
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Coro achieves that by supporting multiple running interpreters that |
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share data, which is especially useful to code pseudo-parallel processes |
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and for event-based programming, such as multiple HTTP-GET requests |
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running concurrently. See Coro::AnyEvent to learn more on how to |
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integrate Coro into an event-based environment. |
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In this module, a thread is defined as "callchain + lexical variables + |
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@_ + $_ + $@ + $/ + C stack), that is, a thread has its own callchain, |
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its own set of lexicals and its own set of perls most important global |
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variables (see Coro::State for more configuration and background info). |
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See also the "SEE ALSO" section at the end of this document - the Coro |
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module family is quite large. |
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GLOBAL VARIABLES |
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$Coro::main |
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This variable stores the coroutine object that represents the main |
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program. While you cna "ready" it and do most other things you can |
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do to coroutines, it is mainly useful to compare again |
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1.15 |
$Coro::current, to see whether you are running in the main program |
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or not. |
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1.14 |
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$Coro::current |
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The coroutine object representing the current coroutine (the last |
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coroutine that the Coro scheduler switched to). The initial value is |
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$Coro::main (of course). |
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This variable is strictly *read-only*. You can take copies of the |
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value stored in it and use it as any other coroutine object, but you |
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must not otherwise modify the variable itself. |
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$Coro::idle |
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This variable is mainly useful to integrate Coro into event loops. |
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It is usually better to rely on Coro::AnyEvent or Coro::EV, as this |
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is pretty low-level functionality. |
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This variable stores either a coroutine or a callback. |
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If it is a callback, the it is called whenever the scheduler finds |
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no ready coroutines to run. The default implementation prints |
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"FATAL: deadlock detected" and exits, because the program has no |
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other way to continue. |
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If it is a coroutine object, then this object will be readied |
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(without invoking any ready hooks, however) when the scheduler finds |
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no other ready coroutines to run. |
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|
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This hook is overwritten by modules such as "Coro::EV" and |
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"Coro::AnyEvent" to wait on an external event that hopefully wake up |
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a coroutine so the scheduler can run it. |
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1.1 |
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1.14 |
Note that the callback *must not*, under any circumstances, block |
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the current coroutine. Normally, this is achieved by having an "idle |
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coroutine" that calls the event loop and then blocks again, and then |
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1.19 |
readying that coroutine in the idle handler, or by simply placing |
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the idle coroutine in this variable. |
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1.4 |
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See Coro::Event or Coro::AnyEvent for examples of using this |
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technique. |
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1.4 |
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Please note that if your callback recursively invokes perl (e.g. for |
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1.12 |
event handlers), then it must be prepared to be called recursively |
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itself. |
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1.1 |
|
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1.19 |
SIMPLE COROUTINE CREATION |
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async { ... } [@args...] |
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1.20 |
Create a new coroutine and return its coroutine object (usually |
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unused). The coroutine will be put into the ready queue, so it will |
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start running automatically on the next scheduler run. |
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1.1 |
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The first argument is a codeblock/closure that should be executed in |
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the coroutine. When it returns argument returns the coroutine is |
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1.1 |
automatically terminated. |
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The remaining arguments are passed as arguments to the closure. |
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1.10 |
See the "Coro::State::new" constructor for info about the coroutine |
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environment in which coroutines are executed. |
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1.10 |
|
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1.7 |
Calling "exit" in a coroutine will do the same as calling exit |
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outside the coroutine. Likewise, when the coroutine dies, the |
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program will exit, just as it would in the main program. |
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1.3 |
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If you do not want that, you can provide a default "die" handler, or |
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simply avoid dieing (by use of "eval"). |
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Example: Create a new coroutine that just prints its arguments. |
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async { |
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print "@_\n"; |
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} 1,2,3,4; |
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1.6 |
async_pool { ... } [@args...] |
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Similar to "async", but uses a coroutine pool, so you should not |
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call terminate or join on it (although you are allowed to), and you |
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get a coroutine that might have executed other code already (which |
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can be good or bad :). |
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1.18 |
On the plus side, this function is about twice as fast as creating |
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(and destroying) a completely new coroutine, so if you need a lot of |
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1.14 |
generic coroutines in quick successsion, use "async_pool", not |
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"async". |
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1.6 |
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The code block is executed in an "eval" context and a warning will |
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1.6 |
be issued in case of an exception instead of terminating the |
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program, as "async" does. As the coroutine is being reused, stuff |
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like "on_destroy" will not work in the expected way, unless you call |
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1.14 |
terminate or cancel, which somehow defeats the purpose of pooling |
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(but is fine in the exceptional case). |
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1.6 |
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1.14 |
The priority will be reset to 0 after each run, tracing will be |
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1.10 |
disabled, the description will be reset and the default output |
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1.14 |
filehandle gets restored, so you can change all these. Otherwise the |
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coroutine will be re-used "as-is": most notably if you change other |
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1.16 |
per-coroutine global stuff such as $/ you *must needs* revert that |
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change, which is most simply done by using local as in: "local $/". |
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The idle pool size is limited to 8 idle coroutines (this can be |
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adjusted by changing $Coro::POOL_SIZE), but there can be as many |
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non-idle coros as required. |
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1.6 |
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If you are concerned about pooled coroutines growing a lot because a |
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single "async_pool" used a lot of stackspace you can e.g. |
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"async_pool { terminate }" once per second or so to slowly replenish |
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1.9 |
the pool. In addition to that, when the stacks used by a handler |
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1.19 |
grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also |
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1.14 |
be destroyed. |
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1.19 |
STATIC METHODS |
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Static methods are actually functions that implicitly operate on the |
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current coroutine. |
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1.6 |
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1.1 |
schedule |
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Calls the scheduler. The scheduler will find the next coroutine that |
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is to be run from the ready queue and switches to it. The next |
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coroutine to be run is simply the one with the highest priority that |
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is longest in its ready queue. If there is no coroutine ready, it |
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will clal the $Coro::idle hook. |
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Please note that the current coroutine will *not* be put into the |
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ready queue, so calling this function usually means you will never |
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be called again unless something else (e.g. an event handler) calls |
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"->ready", thus waking you up. |
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This makes "schedule" *the* generic method to use to block the |
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current coroutine and wait for events: first you remember the |
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current coroutine in a variable, then arrange for some callback of |
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yours to call "->ready" on that once some event happens, and last |
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you call "schedule" to put yourself to sleep. Note that a lot of |
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1.15 |
things can wake your coroutine up, so you need to check whether the |
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1.14 |
event indeed happened, e.g. by storing the status in a variable. |
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1.4 |
|
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1.18 |
See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for |
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callbacks. |
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1.1 |
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cede |
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1.4 |
"Cede" to other coroutines. This function puts the current coroutine |
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1.1 |
into the ready queue and calls "schedule", which has the effect of |
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giving up the current "timeslice" to other coroutines of the same or |
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1.14 |
higher priority. Once your coroutine gets its turn again it will |
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automatically be resumed. |
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This function is often called "yield" in other languages. |
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1.1 |
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1.6 |
Coro::cede_notself |
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1.14 |
Works like cede, but is not exported by default and will cede to |
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*any* coroutine, regardless of priority. This is useful sometimes to |
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ensure progress is made. |
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1.6 |
|
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1.1 |
terminate [arg...] |
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1.4 |
Terminates the current coroutine with the given status values (see |
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1.1 |
cancel). |
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1.10 |
killall |
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Kills/terminates/cancels all coroutines except the currently running |
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one. This is useful after a fork, either in the child or the parent, |
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as usually only one of them should inherit the running coroutines. |
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1.14 |
Note that while this will try to free some of the main programs |
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1.15 |
resources, you cannot free all of them, so if a coroutine that is |
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1.14 |
not the main program calls this function, there will be some |
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one-time resource leak. |
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1.1 |
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1.19 |
COROUTINE OBJECT METHODS |
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1.14 |
These are the methods you can call on coroutine objects (or to create |
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them). |
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1.1 |
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new Coro \&sub [, @args...] |
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1.14 |
Create a new coroutine and return it. When the sub returns, the |
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1.4 |
coroutine automatically terminates as if "terminate" with the |
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returned values were called. To make the coroutine run you must |
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first put it into the ready queue by calling the ready method. |
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1.10 |
See "async" and "Coro::State::new" for additional info about the |
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coroutine environment. |
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1.4 |
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$success = $coroutine->ready |
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1.14 |
Put the given coroutine into the end of its ready queue (there is |
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one queue for each priority) and return true. If the coroutine is |
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already in the ready queue, do nothing and return false. |
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This ensures that the scheduler will resume this coroutine |
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automatically once all the coroutines of higher priority and all |
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coroutines of the same priority that were put into the ready queue |
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earlier have been resumed. |
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1.4 |
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$is_ready = $coroutine->is_ready |
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1.15 |
Return whether the coroutine is currently the ready queue or not, |
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1.4 |
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$coroutine->cancel (arg...) |
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Terminates the given coroutine and makes it return the given |
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1.6 |
arguments as status (default: the empty list). Never returns if the |
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coroutine is the current coroutine. |
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1.1 |
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1.18 |
$coroutine->schedule_to |
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Puts the current coroutine to sleep (like "Coro::schedule"), but |
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instead of continuing with the next coro from the ready queue, |
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always switch to the given coroutine object (regardless of priority |
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etc.). The readyness state of that coroutine isn't changed. |
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This is an advanced method for special cases - I'd love to hear |
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about any uses for this one. |
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$coroutine->cede_to |
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Like "schedule_to", but puts the current coroutine into the ready |
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queue. This has the effect of temporarily switching to the given |
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coroutine, and continuing some time later. |
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This is an advanced method for special cases - I'd love to hear |
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about any uses for this one. |
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1.17 |
$coroutine->throw ([$scalar]) |
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If $throw is specified and defined, it will be thrown as an |
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1.18 |
exception inside the coroutine at the next convenient point in time. |
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1.17 |
Otherwise clears the exception object. |
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1.18 |
Coro will check for the exception each time a schedule-like-function |
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returns, i.e. after each "schedule", "cede", |
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"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of |
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these functions detect this case and return early in case an |
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exception is pending. |
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1.17 |
The exception object will be thrown "as is" with the specified |
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scalar in $@, i.e. if it is a string, no line number or newline will |
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be appended (unlike with "die"). |
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This can be used as a softer means than "cancel" to ask a coroutine |
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to end itself, although there is no guarantee that the exception |
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will lead to termination, and if the exception isn't caught it might |
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well end the whole program. |
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You might also think of "throw" as being the moral equivalent of |
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"kill"ing a coroutine with a signal (in this case, a scalar). |
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1.4 |
$coroutine->join |
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1.1 |
Wait until the coroutine terminates and return any values given to |
304 |
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1.10 |
the "terminate" or "cancel" functions. "join" can be called |
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1.14 |
concurrently from multiple coroutines, and all will be resumed and |
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given the status return once the $coroutine terminates. |
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1.1 |
|
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1.6 |
$coroutine->on_destroy (\&cb) |
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Registers a callback that is called when this coroutine gets |
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destroyed, but before it is joined. The callback gets passed the |
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1.14 |
terminate arguments, if any, and *must not* die, under any |
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circumstances. |
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1.6 |
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1.4 |
$oldprio = $coroutine->prio ($newprio) |
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1.1 |
Sets (or gets, if the argument is missing) the priority of the |
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1.4 |
coroutine. Higher priority coroutines get run before lower priority |
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coroutines. Priorities are small signed integers (currently -4 .. |
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1.1 |
+3), that you can refer to using PRIO_xxx constants (use the import |
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tag :prio to get then): |
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PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
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3 > 1 > 0 > -1 > -3 > -4 |
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# set priority to HIGH |
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current->prio(PRIO_HIGH); |
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The idle coroutine ($Coro::idle) always has a lower priority than |
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any existing coroutine. |
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1.4 |
Changing the priority of the current coroutine will take effect |
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immediately, but changing the priority of coroutines in the ready |
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1.1 |
queue (but not running) will only take effect after the next |
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1.4 |
schedule (of that coroutine). This is a bug that will be fixed in |
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some future version. |
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1.1 |
|
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1.4 |
$newprio = $coroutine->nice ($change) |
337 |
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1.1 |
Similar to "prio", but subtract the given value from the priority |
338 |
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(i.e. higher values mean lower priority, just as in unix). |
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1.4 |
$olddesc = $coroutine->desc ($newdesc) |
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1.1 |
Sets (or gets in case the argument is missing) the description for |
342 |
root |
1.4 |
this coroutine. This is just a free-form string you can associate |
343 |
|
|
with a coroutine. |
344 |
|
|
|
345 |
root |
1.10 |
This method simply sets the "$coroutine->{desc}" member to the given |
346 |
|
|
string. You can modify this member directly if you wish. |
347 |
|
|
|
348 |
root |
1.19 |
GLOBAL FUNCTIONS |
349 |
root |
1.5 |
Coro::nready |
350 |
|
|
Returns the number of coroutines that are currently in the ready |
351 |
root |
1.14 |
state, i.e. that can be switched to by calling "schedule" directory |
352 |
|
|
or indirectly. The value 0 means that the only runnable coroutine is |
353 |
|
|
the currently running one, so "cede" would have no effect, and |
354 |
|
|
"schedule" would cause a deadlock unless there is an idle handler |
355 |
|
|
that wakes up some coroutines. |
356 |
root |
1.5 |
|
357 |
root |
1.6 |
my $guard = Coro::guard { ... } |
358 |
|
|
This creates and returns a guard object. Nothing happens until the |
359 |
root |
1.7 |
object gets destroyed, in which case the codeblock given as argument |
360 |
root |
1.6 |
will be executed. This is useful to free locks or other resources in |
361 |
|
|
case of a runtime error or when the coroutine gets canceled, as in |
362 |
|
|
both cases the guard block will be executed. The guard object |
363 |
|
|
supports only one method, "->cancel", which will keep the codeblock |
364 |
|
|
from being executed. |
365 |
|
|
|
366 |
|
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Example: set some flag and clear it again when the coroutine gets |
367 |
|
|
canceled or the function returns: |
368 |
|
|
|
369 |
|
|
sub do_something { |
370 |
|
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my $guard = Coro::guard { $busy = 0 }; |
371 |
|
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$busy = 1; |
372 |
|
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|
373 |
|
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# do something that requires $busy to be true |
374 |
|
|
} |
375 |
|
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|
376 |
root |
1.4 |
unblock_sub { ... } |
377 |
|
|
This utility function takes a BLOCK or code reference and "unblocks" |
378 |
root |
1.14 |
it, returning a new coderef. Unblocking means that calling the new |
379 |
|
|
coderef will return immediately without blocking, returning nothing, |
380 |
|
|
while the original code ref will be called (with parameters) from |
381 |
|
|
within another coroutine. |
382 |
root |
1.4 |
|
383 |
root |
1.8 |
The reason this function exists is that many event libraries (such |
384 |
root |
1.4 |
as the venerable Event module) are not coroutine-safe (a weaker form |
385 |
root |
1.19 |
of reentrancy). This means you must not block within event |
386 |
root |
1.14 |
callbacks, otherwise you might suffer from crashes or worse. The |
387 |
|
|
only event library currently known that is safe to use without |
388 |
|
|
"unblock_sub" is EV. |
389 |
root |
1.4 |
|
390 |
|
|
This function allows your callbacks to block by executing them in |
391 |
|
|
another coroutine where it is safe to block. One example where |
392 |
|
|
blocking is handy is when you use the Coro::AIO functions to save |
393 |
root |
1.14 |
results to disk, for example. |
394 |
root |
1.4 |
|
395 |
|
|
In short: simply use "unblock_sub { ... }" instead of "sub { ... }" |
396 |
|
|
when creating event callbacks that want to block. |
397 |
root |
1.1 |
|
398 |
root |
1.14 |
If your handler does not plan to block (e.g. simply sends a message |
399 |
|
|
to another coroutine, or puts some other coroutine into the ready |
400 |
|
|
queue), there is no reason to use "unblock_sub". |
401 |
|
|
|
402 |
|
|
Note that you also need to use "unblock_sub" for any other callbacks |
403 |
|
|
that are indirectly executed by any C-based event loop. For example, |
404 |
|
|
when you use a module that uses AnyEvent (and you use |
405 |
|
|
Coro::AnyEvent) and it provides callbacks that are the result of |
406 |
|
|
some event callback, then you must not block either, or use |
407 |
|
|
"unblock_sub". |
408 |
|
|
|
409 |
root |
1.18 |
$cb = Coro::rouse_cb |
410 |
|
|
Create and return a "rouse callback". That's a code reference that, |
411 |
root |
1.19 |
when called, will remember a copy of its arguments and notify the |
412 |
|
|
owner coroutine of the callback. |
413 |
root |
1.18 |
|
414 |
|
|
See the next function. |
415 |
|
|
|
416 |
|
|
@args = Coro::rouse_wait [$cb] |
417 |
root |
1.19 |
Wait for the specified rouse callback (or the last one that was |
418 |
root |
1.18 |
created in this coroutine). |
419 |
|
|
|
420 |
root |
1.19 |
As soon as the callback is invoked (or when the callback was invoked |
421 |
|
|
before "rouse_wait"), it will return the arguments originally passed |
422 |
|
|
to the rouse callback. |
423 |
root |
1.18 |
|
424 |
|
|
See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
425 |
|
|
example. |
426 |
|
|
|
427 |
|
|
HOW TO WAIT FOR A CALLBACK |
428 |
|
|
It is very common for a coroutine to wait for some callback to be |
429 |
|
|
called. This occurs naturally when you use coroutines in an otherwise |
430 |
|
|
event-based program, or when you use event-based libraries. |
431 |
|
|
|
432 |
|
|
These typically register a callback for some event, and call that |
433 |
|
|
callback when the event occured. In a coroutine, however, you typically |
434 |
|
|
want to just wait for the event, simplyifying things. |
435 |
|
|
|
436 |
|
|
For example "AnyEvent->child" registers a callback to be called when a |
437 |
|
|
specific child has exited: |
438 |
|
|
|
439 |
|
|
my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... }); |
440 |
|
|
|
441 |
|
|
But from withina coroutine, you often just want to write this: |
442 |
|
|
|
443 |
|
|
my $status = wait_for_child $pid; |
444 |
|
|
|
445 |
|
|
Coro offers two functions specifically designed to make this easy, |
446 |
|
|
"Coro::rouse_cb" and "Coro::rouse_wait". |
447 |
|
|
|
448 |
|
|
The first function, "rouse_cb", generates and returns a callback that, |
449 |
root |
1.20 |
when invoked, will save its arguments and notify the coroutine that |
450 |
root |
1.18 |
created the callback. |
451 |
|
|
|
452 |
|
|
The second function, "rouse_wait", waits for the callback to be called |
453 |
|
|
(by calling "schedule" to go to sleep) and returns the arguments |
454 |
|
|
originally passed to the callback. |
455 |
|
|
|
456 |
|
|
Using these functions, it becomes easy to write the "wait_for_child" |
457 |
|
|
function mentioned above: |
458 |
|
|
|
459 |
|
|
sub wait_for_child($) { |
460 |
|
|
my ($pid) = @_; |
461 |
|
|
|
462 |
|
|
my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb); |
463 |
|
|
|
464 |
|
|
my ($rpid, $rstatus) = Coro::rouse_wait; |
465 |
|
|
$rstatus |
466 |
|
|
} |
467 |
|
|
|
468 |
|
|
In the case where "rouse_cb" and "rouse_wait" are not flexible enough, |
469 |
|
|
you can roll your own, using "schedule": |
470 |
|
|
|
471 |
|
|
sub wait_for_child($) { |
472 |
|
|
my ($pid) = @_; |
473 |
|
|
|
474 |
|
|
# store the current coroutine in $current, |
475 |
|
|
# and provide result variables for the closure passed to ->child |
476 |
|
|
my $current = $Coro::current; |
477 |
|
|
my ($done, $rstatus); |
478 |
|
|
|
479 |
|
|
# pass a closure to ->child |
480 |
|
|
my $watcher = AnyEvent->child (pid => $pid, cb => sub { |
481 |
|
|
$rstatus = $_[1]; # remember rstatus |
482 |
|
|
$done = 1; # mark $rstatus as valud |
483 |
|
|
}); |
484 |
|
|
|
485 |
|
|
# wait until the closure has been called |
486 |
|
|
schedule while !$done; |
487 |
|
|
|
488 |
|
|
$rstatus |
489 |
|
|
} |
490 |
|
|
|
491 |
root |
1.1 |
BUGS/LIMITATIONS |
492 |
root |
1.18 |
fork with pthread backend |
493 |
|
|
When Coro is compiled using the pthread backend (which isn't |
494 |
|
|
recommended but required on many BSDs as their libcs are completely |
495 |
|
|
broken), then coroutines will not survive a fork. There is no known |
496 |
|
|
workaround except to fix your libc and use a saner backend. |
497 |
|
|
|
498 |
|
|
perl process emulation ("threads") |
499 |
|
|
This module is not perl-pseudo-thread-safe. You should only ever use |
500 |
root |
1.19 |
this module from the first thread (this requirement might be removed |
501 |
root |
1.18 |
in the future to allow per-thread schedulers, but Coro::State does |
502 |
|
|
not yet allow this). I recommend disabling thread support and using |
503 |
|
|
processes, as having the windows process emulation enabled under |
504 |
|
|
unix roughly halves perl performance, even when not used. |
505 |
|
|
|
506 |
|
|
coroutine switching not signal safe |
507 |
|
|
You must not switch to another coroutine from within a signal |
508 |
|
|
handler (only relevant with %SIG - most event libraries provide safe |
509 |
|
|
signals). |
510 |
|
|
|
511 |
|
|
That means you *MUST NOT* call any function that might "block" the |
512 |
|
|
current coroutine - "cede", "schedule" "Coro::Semaphore->down" or |
513 |
|
|
anything that calls those. Everything else, including calling |
514 |
|
|
"ready", works. |
515 |
root |
1.1 |
|
516 |
|
|
SEE ALSO |
517 |
root |
1.14 |
Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
518 |
root |
1.12 |
|
519 |
|
|
Debugging: Coro::Debug. |
520 |
|
|
|
521 |
|
|
Support/Utility: Coro::Specific, Coro::Util. |
522 |
root |
1.2 |
|
523 |
root |
1.19 |
Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, |
524 |
root |
1.2 |
Coro::SemaphoreSet, Coro::RWLock. |
525 |
|
|
|
526 |
root |
1.19 |
I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO. |
527 |
root |
1.14 |
|
528 |
root |
1.19 |
Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP |
529 |
|
|
for a better-working alternative), Coro::BDB, Coro::Storable, |
530 |
|
|
Coro::Select. |
531 |
root |
1.12 |
|
532 |
root |
1.14 |
XS API: Coro::MakeMaker. |
533 |
root |
1.2 |
|
534 |
root |
1.19 |
Low level Configuration, Thread Environment, Continuations: Coro::State. |
535 |
root |
1.1 |
|
536 |
|
|
AUTHOR |
537 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
538 |
|
|
http://home.schmorp.de/ |
539 |
|
|
|