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1.1 |
NAME |
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Coro - coroutine process abstraction |
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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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1.15 |
use Coro::Semaphore; |
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1.14 |
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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This module collection manages coroutines. Coroutines are similar to |
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1.14 |
threads but don't (in general) run in parallel at the same time even on |
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SMP machines. The specific flavor of coroutine used in this module also |
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guarantees you that it will not switch between coroutines unless |
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necessary, at easily-identified points in your program, so locking and |
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parallel access are rarely an issue, making coroutine programming much |
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safer and easier than threads programming. |
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Unlike a normal perl program, however, coroutines allow you to have |
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multiple running interpreters that share data, which is especially |
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useful to code pseudo-parallel processes and for event-based |
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programming, such as multiple HTTP-GET requests running concurrently. |
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See Coro::AnyEvent to learn more. |
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Coroutines are also useful because Perl has no support for threads (the |
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so called "threads" that perl offers are nothing more than the (bad) |
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process emulation coming from the Windows platform: On standard |
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operating systems they serve no purpose whatsoever, except by making |
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your programs slow and making them use a lot of memory. Best disable |
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them when building perl, or aks your software vendor/distributor to do |
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it for you). |
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1.1 |
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In this module, coroutines are defined as "callchain + lexical variables |
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1.5 |
+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own |
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callchain, its own set of lexicals and its own set of perls most |
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1.12 |
important global variables (see Coro::State for more configuration). |
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1.1 |
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1.14 |
$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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1.18 |
$Coro::main (of course). |
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1.14 |
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This variable is strictly *read-only*. You can take copies of the |
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value stored in it and use it as any other coroutine object, but you |
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must not otherwise modify the variable itself. |
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$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 L"Coro::EV", as |
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this is pretty low-level functionality. |
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This variable stores a callback that is called whenever the |
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scheduler finds no ready coroutines to run. The default |
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implementation prints "FATAL: deadlock detected" and exits, because |
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the program has no other way to continue. |
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This hook is overwritten by modules such as "Coro::Timer" 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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readying that coroutine in the idle handler. |
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1.4 |
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1.14 |
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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1.14 |
SIMPLE COROUTINE CREATION |
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async { ... } [@args...] |
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Create a new coroutine and return it's 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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1.14 |
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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1.14 |
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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1.14 |
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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1.14 |
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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1.1 |
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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1.14 |
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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1.14 |
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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1.14 |
grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also |
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be destroyed. |
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STATIC METHODS |
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Static methods are actually functions that operate on the current |
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coroutine. |
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1.6 |
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1.1 |
schedule |
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1.14 |
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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1.4 |
COROUTINE 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 |
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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) |
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1.1 |
Similar to "prio", but subtract the given value from the priority |
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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 |
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1.4 |
this coroutine. This is just a free-form string you can associate |
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with a coroutine. |
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1.10 |
This method simply sets the "$coroutine->{desc}" member to the given |
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string. You can modify this member directly if you wish. |
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|
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1.5 |
GLOBAL FUNCTIONS |
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Coro::nready |
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Returns the number of coroutines that are currently in the ready |
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1.14 |
state, i.e. that can be switched to by calling "schedule" directory |
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or indirectly. The value 0 means that the only runnable coroutine is |
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the currently running one, so "cede" would have no effect, and |
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"schedule" would cause a deadlock unless there is an idle handler |
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that wakes up some coroutines. |
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1.5 |
|
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root |
1.6 |
my $guard = Coro::guard { ... } |
343 |
|
|
This creates and returns a guard object. Nothing happens until the |
344 |
root |
1.7 |
object gets destroyed, in which case the codeblock given as argument |
345 |
root |
1.6 |
will be executed. This is useful to free locks or other resources in |
346 |
|
|
case of a runtime error or when the coroutine gets canceled, as in |
347 |
|
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both cases the guard block will be executed. The guard object |
348 |
|
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supports only one method, "->cancel", which will keep the codeblock |
349 |
|
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from being executed. |
350 |
|
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|
351 |
|
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Example: set some flag and clear it again when the coroutine gets |
352 |
|
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canceled or the function returns: |
353 |
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|
354 |
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sub do_something { |
355 |
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my $guard = Coro::guard { $busy = 0 }; |
356 |
|
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$busy = 1; |
357 |
|
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|
358 |
|
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# do something that requires $busy to be true |
359 |
|
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} |
360 |
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|
361 |
root |
1.4 |
unblock_sub { ... } |
362 |
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This utility function takes a BLOCK or code reference and "unblocks" |
363 |
root |
1.14 |
it, returning a new coderef. Unblocking means that calling the new |
364 |
|
|
coderef will return immediately without blocking, returning nothing, |
365 |
|
|
while the original code ref will be called (with parameters) from |
366 |
|
|
within another coroutine. |
367 |
root |
1.4 |
|
368 |
root |
1.8 |
The reason this function exists is that many event libraries (such |
369 |
root |
1.4 |
as the venerable Event module) are not coroutine-safe (a weaker form |
370 |
|
|
of thread-safety). This means you must not block within event |
371 |
root |
1.14 |
callbacks, otherwise you might suffer from crashes or worse. The |
372 |
|
|
only event library currently known that is safe to use without |
373 |
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|
"unblock_sub" is EV. |
374 |
root |
1.4 |
|
375 |
|
|
This function allows your callbacks to block by executing them in |
376 |
|
|
another coroutine where it is safe to block. One example where |
377 |
|
|
blocking is handy is when you use the Coro::AIO functions to save |
378 |
root |
1.14 |
results to disk, for example. |
379 |
root |
1.4 |
|
380 |
|
|
In short: simply use "unblock_sub { ... }" instead of "sub { ... }" |
381 |
|
|
when creating event callbacks that want to block. |
382 |
root |
1.1 |
|
383 |
root |
1.14 |
If your handler does not plan to block (e.g. simply sends a message |
384 |
|
|
to another coroutine, or puts some other coroutine into the ready |
385 |
|
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queue), there is no reason to use "unblock_sub". |
386 |
|
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|
387 |
|
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Note that you also need to use "unblock_sub" for any other callbacks |
388 |
|
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that are indirectly executed by any C-based event loop. For example, |
389 |
|
|
when you use a module that uses AnyEvent (and you use |
390 |
|
|
Coro::AnyEvent) and it provides callbacks that are the result of |
391 |
|
|
some event callback, then you must not block either, or use |
392 |
|
|
"unblock_sub". |
393 |
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|
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root |
1.18 |
$cb = Coro::rouse_cb |
395 |
|
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Create and return a "rouse callback". That's a code reference that, |
396 |
|
|
when called, will save its arguments and notify the owner coroutine |
397 |
|
|
of the callback. |
398 |
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|
399 |
|
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See the next function. |
400 |
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|
401 |
|
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@args = Coro::rouse_wait [$cb] |
402 |
|
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Wait for the specified rouse callback (or the last one tht was |
403 |
|
|
created in this coroutine). |
404 |
|
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|
405 |
|
|
As soon as the callback is invoked (or when the calback was invoked |
406 |
|
|
before "rouse_wait"), it will return a copy of the arguments |
407 |
|
|
originally passed to the rouse callback. |
408 |
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|
409 |
|
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See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
410 |
|
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example. |
411 |
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|
412 |
|
|
HOW TO WAIT FOR A CALLBACK |
413 |
|
|
It is very common for a coroutine to wait for some callback to be |
414 |
|
|
called. This occurs naturally when you use coroutines in an otherwise |
415 |
|
|
event-based program, or when you use event-based libraries. |
416 |
|
|
|
417 |
|
|
These typically register a callback for some event, and call that |
418 |
|
|
callback when the event occured. In a coroutine, however, you typically |
419 |
|
|
want to just wait for the event, simplyifying things. |
420 |
|
|
|
421 |
|
|
For example "AnyEvent->child" registers a callback to be called when a |
422 |
|
|
specific child has exited: |
423 |
|
|
|
424 |
|
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my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... }); |
425 |
|
|
|
426 |
|
|
But from withina coroutine, you often just want to write this: |
427 |
|
|
|
428 |
|
|
my $status = wait_for_child $pid; |
429 |
|
|
|
430 |
|
|
Coro offers two functions specifically designed to make this easy, |
431 |
|
|
"Coro::rouse_cb" and "Coro::rouse_wait". |
432 |
|
|
|
433 |
|
|
The first function, "rouse_cb", generates and returns a callback that, |
434 |
|
|
when invoked, will save it's arguments and notify the coroutine that |
435 |
|
|
created the callback. |
436 |
|
|
|
437 |
|
|
The second function, "rouse_wait", waits for the callback to be called |
438 |
|
|
(by calling "schedule" to go to sleep) and returns the arguments |
439 |
|
|
originally passed to the callback. |
440 |
|
|
|
441 |
|
|
Using these functions, it becomes easy to write the "wait_for_child" |
442 |
|
|
function mentioned above: |
443 |
|
|
|
444 |
|
|
sub wait_for_child($) { |
445 |
|
|
my ($pid) = @_; |
446 |
|
|
|
447 |
|
|
my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb); |
448 |
|
|
|
449 |
|
|
my ($rpid, $rstatus) = Coro::rouse_wait; |
450 |
|
|
$rstatus |
451 |
|
|
} |
452 |
|
|
|
453 |
|
|
In the case where "rouse_cb" and "rouse_wait" are not flexible enough, |
454 |
|
|
you can roll your own, using "schedule": |
455 |
|
|
|
456 |
|
|
sub wait_for_child($) { |
457 |
|
|
my ($pid) = @_; |
458 |
|
|
|
459 |
|
|
# store the current coroutine in $current, |
460 |
|
|
# and provide result variables for the closure passed to ->child |
461 |
|
|
my $current = $Coro::current; |
462 |
|
|
my ($done, $rstatus); |
463 |
|
|
|
464 |
|
|
# pass a closure to ->child |
465 |
|
|
my $watcher = AnyEvent->child (pid => $pid, cb => sub { |
466 |
|
|
$rstatus = $_[1]; # remember rstatus |
467 |
|
|
$done = 1; # mark $rstatus as valud |
468 |
|
|
}); |
469 |
|
|
|
470 |
|
|
# wait until the closure has been called |
471 |
|
|
schedule while !$done; |
472 |
|
|
|
473 |
|
|
$rstatus |
474 |
|
|
} |
475 |
|
|
|
476 |
root |
1.1 |
BUGS/LIMITATIONS |
477 |
root |
1.18 |
fork with pthread backend |
478 |
|
|
When Coro is compiled using the pthread backend (which isn't |
479 |
|
|
recommended but required on many BSDs as their libcs are completely |
480 |
|
|
broken), then coroutines will not survive a fork. There is no known |
481 |
|
|
workaround except to fix your libc and use a saner backend. |
482 |
|
|
|
483 |
|
|
perl process emulation ("threads") |
484 |
|
|
This module is not perl-pseudo-thread-safe. You should only ever use |
485 |
|
|
this module from the same thread (this requirement might be removed |
486 |
|
|
in the future to allow per-thread schedulers, but Coro::State does |
487 |
|
|
not yet allow this). I recommend disabling thread support and using |
488 |
|
|
processes, as having the windows process emulation enabled under |
489 |
|
|
unix roughly halves perl performance, even when not used. |
490 |
|
|
|
491 |
|
|
coroutine switching not signal safe |
492 |
|
|
You must not switch to another coroutine from within a signal |
493 |
|
|
handler (only relevant with %SIG - most event libraries provide safe |
494 |
|
|
signals). |
495 |
|
|
|
496 |
|
|
That means you *MUST NOT* call any function that might "block" the |
497 |
|
|
current coroutine - "cede", "schedule" "Coro::Semaphore->down" or |
498 |
|
|
anything that calls those. Everything else, including calling |
499 |
|
|
"ready", works. |
500 |
root |
1.1 |
|
501 |
|
|
SEE ALSO |
502 |
root |
1.14 |
Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
503 |
root |
1.12 |
|
504 |
|
|
Debugging: Coro::Debug. |
505 |
|
|
|
506 |
|
|
Support/Utility: Coro::Specific, Coro::Util. |
507 |
root |
1.2 |
|
508 |
|
|
Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, |
509 |
|
|
Coro::SemaphoreSet, Coro::RWLock. |
510 |
|
|
|
511 |
root |
1.14 |
IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO. |
512 |
|
|
|
513 |
|
|
Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select. |
514 |
root |
1.12 |
|
515 |
root |
1.14 |
XS API: Coro::MakeMaker. |
516 |
root |
1.2 |
|
517 |
root |
1.14 |
Low level Configuration, Coroutine Environment: Coro::State. |
518 |
root |
1.1 |
|
519 |
|
|
AUTHOR |
520 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
521 |
|
|
http://home.schmorp.de/ |
522 |
|
|
|