1 |
NAME |
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Coro - the only real threads in perl |
3 |
|
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SYNOPSIS |
5 |
use Coro; |
6 |
|
7 |
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 coro |
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print "3\n"; |
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cede; # and again |
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|
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# use locking |
19 |
use Coro::Semaphore; |
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my $lock = new Coro::Semaphore; |
21 |
my $locked; |
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|
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$lock->down; |
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$locked = 1; |
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$lock->up; |
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|
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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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|
31 |
This module collection manages continuations in general, most often in |
32 |
the form of cooperative threads (also called coros, or simply "coro" in |
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the 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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|
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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, and as such act |
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as processes), Coro provides a full shared address space, which makes |
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communication between threads very easy. And Coro's threads are fast, |
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too: disabling the Windows process emulation code in your perl and using |
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Coro can easily result in a two to four times speed increase for your |
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programs. A parallel matrix multiplication benchmark runs over 300 times |
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faster on a single core than perl's pseudo-threads on a quad core using |
49 |
all four cores. |
50 |
|
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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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|
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In this module, a thread is defined as "callchain + lexical variables + |
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some package variables + C stack), that is, a thread has its own |
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callchain, its own set of lexicals and its own set of perls most |
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important global variables (see Coro::State for more configuration and |
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background info). |
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|
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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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|
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GLOBAL VARIABLES |
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$Coro::main |
68 |
This variable stores the Coro 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 coro, it is mainly useful to compare again $Coro::current, to |
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see whether you are running in the main program or not. |
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|
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$Coro::current |
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The Coro object representing the current coro (the last coro that |
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the Coro scheduler switched to). The initial value is $Coro::main |
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(of course). |
77 |
|
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This variable is strictly *read-only*. You can take copies of the |
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value stored in it and use it as any other Coro object, but you must |
80 |
not otherwise modify the variable itself. |
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|
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$Coro::idle |
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This variable is mainly useful to integrate Coro into event loops. |
84 |
It is usually better to rely on Coro::AnyEvent or Coro::EV, as this |
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is pretty low-level functionality. |
86 |
|
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This variable stores either a Coro object or a callback. |
88 |
|
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If it is a callback, the it is called whenever the scheduler finds |
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no ready coros to run. The default implementation prints "FATAL: |
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deadlock detected" and exits, because the program has no other way |
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to continue. |
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|
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If it is a coro object, then this object will be readied (without |
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invoking any ready hooks, however) when the scheduler finds no other |
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ready coros to run. |
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|
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This hook is overwritten by modules such as "Coro::EV" and |
99 |
"Coro::AnyEvent" to wait on an external event that hopefully wake up |
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a coro so the scheduler can run it. |
101 |
|
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Note that the callback *must not*, under any circumstances, block |
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the current coro. Normally, this is achieved by having an "idle |
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coro" that calls the event loop and then blocks again, and then |
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readying that coro in the idle handler, or by simply placing the |
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idle coro in this variable. |
107 |
|
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See Coro::Event or Coro::AnyEvent for examples of using this |
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technique. |
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|
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Please note that if your callback recursively invokes perl (e.g. for |
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event handlers), then it must be prepared to be called recursively |
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itself. |
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|
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SIMPLE CORO CREATION |
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async { ... } [@args...] |
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Create a new coro and return its Coro object (usually unused). The |
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coro will be put into the ready queue, so it will start running |
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automatically on the next scheduler run. |
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|
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The first argument is a codeblock/closure that should be executed in |
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the coro. When it returns argument returns the coro is automatically |
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terminated. |
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|
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The remaining arguments are passed as arguments to the closure. |
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|
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See the "Coro::State::new" constructor for info about the coro |
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environment in which coro are executed. |
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|
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Calling "exit" in a coro will do the same as calling exit outside |
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the coro. Likewise, when the coro dies, the program will exit, just |
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as it would in the main program. |
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|
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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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|
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Example: Create a new coro that just prints its arguments. |
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|
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async { |
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print "@_\n"; |
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} 1,2,3,4; |
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|
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async_pool { ... } [@args...] |
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Similar to "async", but uses a coro pool, so you should not call |
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terminate or join on it (although you are allowed to), and you get a |
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coro that might have executed other code already (which can be good |
147 |
or bad :). |
148 |
|
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On the plus side, this function is about twice as fast as creating |
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(and destroying) a completely new coro, so if you need a lot of |
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generic coros in quick successsion, use "async_pool", not "async". |
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|
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The code block is executed in an "eval" context and a warning will |
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be issued in case of an exception instead of terminating the |
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program, as "async" does. As the coro is being reused, stuff like |
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"on_destroy" will not work in the expected way, unless you call |
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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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|
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The priority will be reset to 0 after each run, tracing will be |
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disabled, the description will be reset and the default output |
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filehandle gets restored, so you can change all these. Otherwise the |
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coro will be re-used "as-is": most notably if you change other |
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per-coro 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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|
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The idle pool size is limited to 8 idle coros (this can be adjusted |
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by changing $Coro::POOL_SIZE), but there can be as many non-idle |
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coros as required. |
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|
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If you are concerned about pooled coros 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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the pool. In addition to that, when the stacks used by a handler |
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grows larger than 32kb (adjustable via $Coro::POOL_RSS) it will also |
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be destroyed. |
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|
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STATIC METHODS |
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Static methods are actually functions that implicitly operate on the |
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current coro. |
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|
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schedule |
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Calls the scheduler. The scheduler will find the next coro that is |
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to be run from the ready queue and switches to it. The next coro to |
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be run is simply the one with the highest priority that is longest |
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in its ready queue. If there is no coro ready, it will clal the |
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$Coro::idle hook. |
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|
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Please note that the current coro will *not* be put into the ready |
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queue, so calling this function usually means you will never be |
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called again unless something else (e.g. an event handler) calls |
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"->ready", thus waking you up. |
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|
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This makes "schedule" *the* generic method to use to block the |
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current coro and wait for events: first you remember the current |
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coro in a variable, then arrange for some callback of yours to call |
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"->ready" on that once some event happens, and last you call |
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"schedule" to put yourself to sleep. Note that a lot of things can |
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wake your coro up, so you need to check whether the event indeed |
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happened, e.g. by storing the status in a variable. |
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|
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See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for |
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callbacks. |
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|
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cede |
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"Cede" to other coros. This function puts the current coro into the |
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ready queue and calls "schedule", which has the effect of giving up |
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the current "timeslice" to other coros of the same or higher |
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priority. Once your coro gets its turn again it will automatically |
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be resumed. |
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|
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This function is often called "yield" in other languages. |
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|
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Coro::cede_notself |
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Works like cede, but is not exported by default and will cede to |
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*any* coro, regardless of priority. This is useful sometimes to |
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ensure progress is made. |
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|
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terminate [arg...] |
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Terminates the current coro with the given status values (see |
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cancel). |
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|
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Coro::on_enter BLOCK, Coro::on_leave BLOCK |
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These function install enter and leave winders in the current scope. |
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The enter block will be executed when on_enter is called and |
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whenever the current coro is re-entered by the scheduler, while the |
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leave block is executed whenever the current coro is blocked by the |
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scheduler, and also when the containing scope is exited (by whatever |
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means, be it exit, die, last etc.). |
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|
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*Neither invoking the scheduler, nor exceptions, are allowed within |
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those BLOCKs*. That means: do not even think about calling "die" |
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without an eval, and do not even think of entering the scheduler in |
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any way. |
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|
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Since both BLOCKs are tied to the current scope, they will |
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automatically be removed when the current scope exits. |
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|
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These functions implement the same concept as "dynamic-wind" in |
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scheme does, and are useful when you want to localise some resource |
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to a specific coro. |
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|
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They slow down coro switching considerably for coros that use them |
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(But coro switching is still reasonably fast if the handlers are |
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fast). |
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|
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These functions are best understood by an example: The following |
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function will change the current timezone to |
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"Antarctica/South_Pole", which requires a call to "tzset", but by |
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using "on_enter" and "on_leave", which remember/change the current |
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timezone and restore the previous value, respectively, the timezone |
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is only changes for the coro that installed those handlers. |
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|
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use POSIX qw(tzset); |
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|
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async { |
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my $old_tz; # store outside TZ value here |
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|
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Coro::on_enter { |
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$old_tz = $ENV{TZ}; # remember the old value |
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|
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$ENV{TZ} = "Antarctica/South_Pole"; |
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tzset; # enable new value |
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}; |
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|
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Coro::on_leave { |
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$ENV{TZ} = $old_tz; |
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tzset; # restore old value |
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}; |
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|
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# at this place, the timezone is Antarctica/South_Pole, |
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# without disturbing the TZ of any other coro. |
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}; |
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|
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This can be used to localise about any resource (locale, uid, |
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current working directory etc.) to a block, despite the existance of |
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other coros. |
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|
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killall |
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Kills/terminates/cancels all coros except the currently running one. |
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|
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Note that while this will try to free some of the main interpreter |
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resources if the calling coro isn't the main coro, but one cannot |
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free all of them, so if a coro that is not the main coro calls this |
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function, there will be some one-time resource leak. |
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|
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CORO OBJECT METHODS |
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These are the methods you can call on coro objects (or to create them). |
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|
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new Coro \&sub [, @args...] |
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Create a new coro and return it. When the sub returns, the coro |
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automatically terminates as if "terminate" with the returned values |
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were called. To make the coro run you must first put it into the |
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ready queue by calling the ready method. |
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|
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See "async" and "Coro::State::new" for additional info about the |
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coro environment. |
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|
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$success = $coro->ready |
300 |
Put the given coro into the end of its ready queue (there is one |
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queue for each priority) and return true. If the coro is already in |
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the ready queue, do nothing and return false. |
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|
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This ensures that the scheduler will resume this coro automatically |
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once all the coro of higher priority and all coro of the same |
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priority that were put into the ready queue earlier have been |
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resumed. |
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|
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$coro->suspend |
310 |
Suspends the specified coro. A suspended coro works just like any |
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other coro, except that the scheduler will not select a suspended |
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coro for execution. |
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|
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Suspending a coro can be useful when you want to keep the coro from |
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running, but you don't want to destroy it, or when you want to |
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temporarily freeze a coro (e.g. for debugging) to resume it later. |
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|
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A scenario for the former would be to suspend all (other) coros |
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after a fork and keep them alive, so their destructors aren't |
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called, but new coros can be created. |
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|
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$coro->resume |
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If the specified coro was suspended, it will be resumed. Note that |
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when the coro was in the ready queue when it was suspended, it might |
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have been unreadied by the scheduler, so an activation might have |
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been lost. |
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|
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To avoid this, it is best to put a suspended coro into the ready |
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queue unconditionally, as every synchronisation mechanism must |
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protect itself against spurious wakeups, and the one in the Coro |
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family certainly do that. |
332 |
|
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$is_ready = $coro->is_ready |
334 |
Returns true iff the Coro object is in the ready queue. Unless the |
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Coro object gets destroyed, it will eventually be scheduled by the |
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scheduler. |
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|
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$is_running = $coro->is_running |
339 |
Returns true iff the Coro object is currently running. Only one Coro |
340 |
object can ever be in the running state (but it currently is |
341 |
possible to have multiple running Coro::States). |
342 |
|
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$is_suspended = $coro->is_suspended |
344 |
Returns true iff this Coro object has been suspended. Suspended |
345 |
Coros will not ever be scheduled. |
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|
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$coro->cancel (arg...) |
348 |
Terminates the given Coro and makes it return the given arguments as |
349 |
status (default: the empty list). Never returns if the Coro is the |
350 |
current Coro. |
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|
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$coro->schedule_to |
353 |
Puts the current coro to sleep (like "Coro::schedule"), but instead |
354 |
of continuing with the next coro from the ready queue, always switch |
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to the given coro object (regardless of priority etc.). The |
356 |
readyness state of that coro isn't changed. |
357 |
|
358 |
This is an advanced method for special cases - I'd love to hear |
359 |
about any uses for this one. |
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|
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$coro->cede_to |
362 |
Like "schedule_to", but puts the current coro into the ready queue. |
363 |
This has the effect of temporarily switching to the given coro, and |
364 |
continuing some time later. |
365 |
|
366 |
This is an advanced method for special cases - I'd love to hear |
367 |
about any uses for this one. |
368 |
|
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$coro->throw ([$scalar]) |
370 |
If $throw is specified and defined, it will be thrown as an |
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exception inside the coro at the next convenient point in time. |
372 |
Otherwise clears the exception object. |
373 |
|
374 |
Coro will check for the exception each time a schedule-like-function |
375 |
returns, i.e. after each "schedule", "cede", |
376 |
"Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of |
377 |
these functions detect this case and return early in case an |
378 |
exception is pending. |
379 |
|
380 |
The exception object will be thrown "as is" with the specified |
381 |
scalar in $@, i.e. if it is a string, no line number or newline will |
382 |
be appended (unlike with "die"). |
383 |
|
384 |
This can be used as a softer means than "cancel" to ask a coro to |
385 |
end itself, although there is no guarantee that the exception will |
386 |
lead to termination, and if the exception isn't caught it might well |
387 |
end the whole program. |
388 |
|
389 |
You might also think of "throw" as being the moral equivalent of |
390 |
"kill"ing a coro with a signal (in this case, a scalar). |
391 |
|
392 |
$coro->join |
393 |
Wait until the coro terminates and return any values given to the |
394 |
"terminate" or "cancel" functions. "join" can be called concurrently |
395 |
from multiple coro, and all will be resumed and given the status |
396 |
return once the $coro terminates. |
397 |
|
398 |
$coro->on_destroy (\&cb) |
399 |
Registers a callback that is called when this coro gets destroyed, |
400 |
but before it is joined. The callback gets passed the terminate |
401 |
arguments, if any, and *must not* die, under any circumstances. |
402 |
|
403 |
$oldprio = $coro->prio ($newprio) |
404 |
Sets (or gets, if the argument is missing) the priority of the coro. |
405 |
Higher priority coro get run before lower priority coro. Priorities |
406 |
are small signed integers (currently -4 .. +3), that you can refer |
407 |
to using PRIO_xxx constants (use the import tag :prio to get then): |
408 |
|
409 |
PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
410 |
3 > 1 > 0 > -1 > -3 > -4 |
411 |
|
412 |
# set priority to HIGH |
413 |
current->prio (PRIO_HIGH); |
414 |
|
415 |
The idle coro ($Coro::idle) always has a lower priority than any |
416 |
existing coro. |
417 |
|
418 |
Changing the priority of the current coro will take effect |
419 |
immediately, but changing the priority of coro in the ready queue |
420 |
(but not running) will only take effect after the next schedule (of |
421 |
that coro). This is a bug that will be fixed in some future version. |
422 |
|
423 |
$newprio = $coro->nice ($change) |
424 |
Similar to "prio", but subtract the given value from the priority |
425 |
(i.e. higher values mean lower priority, just as in unix). |
426 |
|
427 |
$olddesc = $coro->desc ($newdesc) |
428 |
Sets (or gets in case the argument is missing) the description for |
429 |
this coro. This is just a free-form string you can associate with a |
430 |
coro. |
431 |
|
432 |
This method simply sets the "$coro->{desc}" member to the given |
433 |
string. You can modify this member directly if you wish. |
434 |
|
435 |
GLOBAL FUNCTIONS |
436 |
Coro::nready |
437 |
Returns the number of coro that are currently in the ready state, |
438 |
i.e. that can be switched to by calling "schedule" directory or |
439 |
indirectly. The value 0 means that the only runnable coro is the |
440 |
currently running one, so "cede" would have no effect, and |
441 |
"schedule" would cause a deadlock unless there is an idle handler |
442 |
that wakes up some coro. |
443 |
|
444 |
my $guard = Coro::guard { ... } |
445 |
This function still exists, but is deprecated. Please use the |
446 |
"Guard::guard" function instead. |
447 |
|
448 |
unblock_sub { ... } |
449 |
This utility function takes a BLOCK or code reference and "unblocks" |
450 |
it, returning a new coderef. Unblocking means that calling the new |
451 |
coderef will return immediately without blocking, returning nothing, |
452 |
while the original code ref will be called (with parameters) from |
453 |
within another coro. |
454 |
|
455 |
The reason this function exists is that many event libraries (such |
456 |
as the venerable Event module) are not thread-safe (a weaker form of |
457 |
reentrancy). This means you must not block within event callbacks, |
458 |
otherwise you might suffer from crashes or worse. The only event |
459 |
library currently known that is safe to use without "unblock_sub" is |
460 |
EV. |
461 |
|
462 |
This function allows your callbacks to block by executing them in |
463 |
another coro where it is safe to block. One example where blocking |
464 |
is handy is when you use the Coro::AIO functions to save results to |
465 |
disk, for example. |
466 |
|
467 |
In short: simply use "unblock_sub { ... }" instead of "sub { ... }" |
468 |
when creating event callbacks that want to block. |
469 |
|
470 |
If your handler does not plan to block (e.g. simply sends a message |
471 |
to another coro, or puts some other coro into the ready queue), |
472 |
there is no reason to use "unblock_sub". |
473 |
|
474 |
Note that you also need to use "unblock_sub" for any other callbacks |
475 |
that are indirectly executed by any C-based event loop. For example, |
476 |
when you use a module that uses AnyEvent (and you use |
477 |
Coro::AnyEvent) and it provides callbacks that are the result of |
478 |
some event callback, then you must not block either, or use |
479 |
"unblock_sub". |
480 |
|
481 |
$cb = Coro::rouse_cb |
482 |
Create and return a "rouse callback". That's a code reference that, |
483 |
when called, will remember a copy of its arguments and notify the |
484 |
owner coro of the callback. |
485 |
|
486 |
See the next function. |
487 |
|
488 |
@args = Coro::rouse_wait [$cb] |
489 |
Wait for the specified rouse callback (or the last one that was |
490 |
created in this coro). |
491 |
|
492 |
As soon as the callback is invoked (or when the callback was invoked |
493 |
before "rouse_wait"), it will return the arguments originally passed |
494 |
to the rouse callback. |
495 |
|
496 |
See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
497 |
example. |
498 |
|
499 |
HOW TO WAIT FOR A CALLBACK |
500 |
It is very common for a coro to wait for some callback to be called. |
501 |
This occurs naturally when you use coro in an otherwise event-based |
502 |
program, or when you use event-based libraries. |
503 |
|
504 |
These typically register a callback for some event, and call that |
505 |
callback when the event occured. In a coro, however, you typically want |
506 |
to just wait for the event, simplyifying things. |
507 |
|
508 |
For example "AnyEvent->child" registers a callback to be called when a |
509 |
specific child has exited: |
510 |
|
511 |
my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... }); |
512 |
|
513 |
But from within a coro, you often just want to write this: |
514 |
|
515 |
my $status = wait_for_child $pid; |
516 |
|
517 |
Coro offers two functions specifically designed to make this easy, |
518 |
"Coro::rouse_cb" and "Coro::rouse_wait". |
519 |
|
520 |
The first function, "rouse_cb", generates and returns a callback that, |
521 |
when invoked, will save its arguments and notify the coro that created |
522 |
the callback. |
523 |
|
524 |
The second function, "rouse_wait", waits for the callback to be called |
525 |
(by calling "schedule" to go to sleep) and returns the arguments |
526 |
originally passed to the callback. |
527 |
|
528 |
Using these functions, it becomes easy to write the "wait_for_child" |
529 |
function mentioned above: |
530 |
|
531 |
sub wait_for_child($) { |
532 |
my ($pid) = @_; |
533 |
|
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my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb); |
535 |
|
536 |
my ($rpid, $rstatus) = Coro::rouse_wait; |
537 |
$rstatus |
538 |
} |
539 |
|
540 |
In the case where "rouse_cb" and "rouse_wait" are not flexible enough, |
541 |
you can roll your own, using "schedule": |
542 |
|
543 |
sub wait_for_child($) { |
544 |
my ($pid) = @_; |
545 |
|
546 |
# store the current coro in $current, |
547 |
# and provide result variables for the closure passed to ->child |
548 |
my $current = $Coro::current; |
549 |
my ($done, $rstatus); |
550 |
|
551 |
# pass a closure to ->child |
552 |
my $watcher = AnyEvent->child (pid => $pid, cb => sub { |
553 |
$rstatus = $_[1]; # remember rstatus |
554 |
$done = 1; # mark $rstatus as valud |
555 |
}); |
556 |
|
557 |
# wait until the closure has been called |
558 |
schedule while !$done; |
559 |
|
560 |
$rstatus |
561 |
} |
562 |
|
563 |
BUGS/LIMITATIONS |
564 |
fork with pthread backend |
565 |
When Coro is compiled using the pthread backend (which isn't |
566 |
recommended but required on many BSDs as their libcs are completely |
567 |
broken), then coro will not survive a fork. There is no known |
568 |
workaround except to fix your libc and use a saner backend. |
569 |
|
570 |
perl process emulation ("threads") |
571 |
This module is not perl-pseudo-thread-safe. You should only ever use |
572 |
this module from the first thread (this requirement might be removed |
573 |
in the future to allow per-thread schedulers, but Coro::State does |
574 |
not yet allow this). I recommend disabling thread support and using |
575 |
processes, as having the windows process emulation enabled under |
576 |
unix roughly halves perl performance, even when not used. |
577 |
|
578 |
coro switching is not signal safe |
579 |
You must not switch to another coro from within a signal handler |
580 |
(only relevant with %SIG - most event libraries provide safe |
581 |
signals). |
582 |
|
583 |
That means you *MUST NOT* call any function that might "block" the |
584 |
current coro - "cede", "schedule" "Coro::Semaphore->down" or |
585 |
anything that calls those. Everything else, including calling |
586 |
"ready", works. |
587 |
|
588 |
SEE ALSO |
589 |
Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
590 |
|
591 |
Debugging: Coro::Debug. |
592 |
|
593 |
Support/Utility: Coro::Specific, Coro::Util. |
594 |
|
595 |
Locking and IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, |
596 |
Coro::SemaphoreSet, Coro::RWLock. |
597 |
|
598 |
I/O and Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO. |
599 |
|
600 |
Compatibility with other modules: Coro::LWP (but see also AnyEvent::HTTP |
601 |
for a better-working alternative), Coro::BDB, Coro::Storable, |
602 |
Coro::Select. |
603 |
|
604 |
XS API: Coro::MakeMaker. |
605 |
|
606 |
Low level Configuration, Thread Environment, Continuations: Coro::State. |
607 |
|
608 |
AUTHOR |
609 |
Marc Lehmann <schmorp@schmorp.de> |
610 |
http://home.schmorp.de/ |
611 |
|