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NAME |
| 2 |
Coro - coroutine process abstraction |
| 3 |
|
| 4 |
SYNOPSIS |
| 5 |
use Coro; |
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|
| 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 coroutine |
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print "3\n"; |
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cede; # and again |
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|
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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 $locked; |
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|
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$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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This module collection manages coroutines. Coroutines are similar to |
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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 |
| 31 |
guarantees you that it will not switch between coroutines unless |
| 32 |
necessary, at easily-identified points in your program, so locking and |
| 33 |
parallel access are rarely an issue, making coroutine programming much |
| 34 |
safer and easier than threads programming. |
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|
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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 |
| 39 |
programming, such as multiple HTTP-GET requests running concurrently. |
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See Coro::AnyEvent to learn more. |
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|
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Coroutines are also useful because Perl has no support for threads (the |
| 43 |
so called "threads" that perl offers are nothing more than the (bad) |
| 44 |
process emulation coming from the Windows platform: On standard |
| 45 |
operating systems they serve no purpose whatsoever, except by making |
| 46 |
your programs slow and making them use a lot of memory. Best disable |
| 47 |
them when building perl, or aks your software vendor/distributor to do |
| 48 |
it for you). |
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|
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In this module, coroutines are defined as "callchain + lexical variables |
| 51 |
+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own |
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callchain, its own set of lexicals and its own set of perls most |
| 53 |
important global variables (see Coro::State for more configuration). |
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|
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$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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$Coro::current, to see whether you are running in the main program |
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or not. |
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|
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$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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$main (of course). |
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|
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This variable is strictly *read-only*. You can take copies of the |
| 68 |
value stored in it and use it as any other coroutine object, but you |
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must not otherwise modify the variable itself. |
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|
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$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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|
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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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|
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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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|
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Note that the callback *must not*, under any circumstances, block |
| 86 |
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 |
| 88 |
readying that coroutine in the idle handler. |
| 89 |
|
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See Coro::Event or Coro::AnyEvent for examples of using this |
| 91 |
technique. |
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|
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Please note that if your callback recursively invokes perl (e.g. for |
| 94 |
event handlers), then it must be prepared to be called recursively |
| 95 |
itself. |
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|
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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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|
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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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automatically 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 coroutine |
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environment in which coroutines are executed. |
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|
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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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|
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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 coroutine 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 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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|
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On the plus side, this function is faster than creating (and |
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destroying) a completly new coroutine, so if you need a lot of |
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generic coroutines in quick successsion, use "async_pool", not |
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"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 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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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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coroutine will be re-used "as-is": most notably if you change other |
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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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|
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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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|
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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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the pool. In addition to that, when the stacks used by a handler |
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grows larger than 16kb (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 operate on the current |
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coroutine. |
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|
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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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|
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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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|
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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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things can wake your coroutine up, so you need to check whether the |
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event indeed happened, e.g. by storing the status in a variable. |
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|
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The canonical way to wait on external events is this: |
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|
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{ |
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# remember current coroutine |
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my $current = $Coro::current; |
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|
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# register a hypothetical event handler |
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on_event_invoke sub { |
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# wake up sleeping coroutine |
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$current->ready; |
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undef $current; |
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}; |
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|
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# call schedule until event occurred. |
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# in case we are woken up for other reasons |
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# (current still defined), loop. |
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Coro::schedule while $current; |
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} |
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|
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cede |
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"Cede" to other coroutines. This function puts the current coroutine |
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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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higher priority. Once your coroutine gets its turn again it will |
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automatically 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* coroutine, 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 coroutine with the given status values (see |
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cancel). |
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|
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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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|
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Note that while this will try to free some of the main programs |
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resources, you cannot free all of them, so if a coroutine that is |
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not the main program calls this function, there will be some |
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one-time resource leak. |
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|
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COROUTINE METHODS |
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These are the methods you can call on coroutine objects (or to create |
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them). |
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|
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new Coro \&sub [, @args...] |
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Create a new coroutine and return it. When the sub returns, the |
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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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|
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See "async" and "Coro::State::new" for additional info about the |
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coroutine environment. |
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|
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$success = $coroutine->ready |
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Put the given coroutine into the end of its ready queue (there is |
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one queue for each priority) and return true. If the coroutine is |
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already in the ready queue, do nothing and return false. |
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|
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This ensures that the scheduler will resume this coroutine |
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automatically once all the coroutines of higher priority and all |
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coroutines of the same priority that were put into the ready queue |
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earlier have been resumed. |
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|
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$is_ready = $coroutine->is_ready |
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Return whether the coroutine is currently the ready queue or not, |
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|
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$coroutine->cancel (arg...) |
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Terminates the given coroutine and makes it return the given |
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arguments as status (default: the empty list). Never returns if the |
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coroutine is the current coroutine. |
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|
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$coroutine->throw ([$scalar]) |
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If $throw is specified and defined, it will be thrown as an |
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exception inside the coroutine at the next convenient point in time |
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(usually after it gains control at the next schedule/transfer/cede). |
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Otherwise clears the exception object. |
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|
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The exception object will be thrown "as is" with the specified |
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scalar in $@, i.e. if it is a string, no line number or newline will |
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be appended (unlike with "die"). |
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|
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This can be used as a softer means than "cancel" to ask a coroutine |
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to end itself, although there is no guarantee that the exception |
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will lead to termination, and if the exception isn't caught it might |
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well end the whole program. |
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|
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You might also think of "throw" as being the moral equivalent of |
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"kill"ing a coroutine with a signal (in this case, a scalar). |
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|
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$coroutine->join |
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Wait until the coroutine terminates and return any values given to |
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the "terminate" or "cancel" functions. "join" can be called |
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concurrently from multiple coroutines, and all will be resumed and |
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given the status return once the $coroutine terminates. |
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|
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$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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terminate arguments, if any, and *must not* die, under any |
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circumstances. |
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|
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$oldprio = $coroutine->prio ($newprio) |
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Sets (or gets, if the argument is missing) the priority of the |
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coroutine. Higher priority coroutines get run before lower priority |
| 296 |
coroutines. Priorities are small signed integers (currently -4 .. |
| 297 |
+3), that you can refer to using PRIO_xxx constants (use the import |
| 298 |
tag :prio to get then): |
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|
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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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|
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# set priority to HIGH |
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current->prio(PRIO_HIGH); |
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|
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The idle coroutine ($Coro::idle) always has a lower priority than |
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any existing coroutine. |
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|
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Changing the priority of the current coroutine will take effect |
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immediately, but changing the priority of coroutines in the ready |
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queue (but not running) will only take effect after the next |
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schedule (of that coroutine). This is a bug that will be fixed in |
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some future version. |
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|
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$newprio = $coroutine->nice ($change) |
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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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|
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$olddesc = $coroutine->desc ($newdesc) |
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Sets (or gets in case the argument is missing) the description for |
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this coroutine. This is just a free-form string you can associate |
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with a coroutine. |
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|
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This method simply sets the "$coroutine->{desc}" member to the given |
| 325 |
string. You can modify this member directly if you wish. |
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|
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GLOBAL FUNCTIONS |
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Coro::nready |
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Returns the number of coroutines that are currently in the ready |
| 330 |
state, i.e. that can be switched to by calling "schedule" directory |
| 331 |
or indirectly. The value 0 means that the only runnable coroutine is |
| 332 |
the currently running one, so "cede" would have no effect, and |
| 333 |
"schedule" would cause a deadlock unless there is an idle handler |
| 334 |
that wakes up some coroutines. |
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|
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my $guard = Coro::guard { ... } |
| 337 |
This creates and returns a guard object. Nothing happens until the |
| 338 |
object gets destroyed, in which case the codeblock given as argument |
| 339 |
will be executed. This is useful to free locks or other resources in |
| 340 |
case of a runtime error or when the coroutine gets canceled, as in |
| 341 |
both cases the guard block will be executed. The guard object |
| 342 |
supports only one method, "->cancel", which will keep the codeblock |
| 343 |
from being executed. |
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|
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Example: set some flag and clear it again when the coroutine gets |
| 346 |
canceled or the function returns: |
| 347 |
|
| 348 |
sub do_something { |
| 349 |
my $guard = Coro::guard { $busy = 0 }; |
| 350 |
$busy = 1; |
| 351 |
|
| 352 |
# do something that requires $busy to be true |
| 353 |
} |
| 354 |
|
| 355 |
unblock_sub { ... } |
| 356 |
This utility function takes a BLOCK or code reference and "unblocks" |
| 357 |
it, returning a new coderef. Unblocking means that calling the new |
| 358 |
coderef will return immediately without blocking, returning nothing, |
| 359 |
while the original code ref will be called (with parameters) from |
| 360 |
within another coroutine. |
| 361 |
|
| 362 |
The reason this function exists is that many event libraries (such |
| 363 |
as the venerable Event module) are not coroutine-safe (a weaker form |
| 364 |
of thread-safety). This means you must not block within event |
| 365 |
callbacks, otherwise you might suffer from crashes or worse. The |
| 366 |
only event library currently known that is safe to use without |
| 367 |
"unblock_sub" is EV. |
| 368 |
|
| 369 |
This function allows your callbacks to block by executing them in |
| 370 |
another coroutine where it is safe to block. One example where |
| 371 |
blocking is handy is when you use the Coro::AIO functions to save |
| 372 |
results to disk, for example. |
| 373 |
|
| 374 |
In short: simply use "unblock_sub { ... }" instead of "sub { ... }" |
| 375 |
when creating event callbacks that want to block. |
| 376 |
|
| 377 |
If your handler does not plan to block (e.g. simply sends a message |
| 378 |
to another coroutine, or puts some other coroutine into the ready |
| 379 |
queue), there is no reason to use "unblock_sub". |
| 380 |
|
| 381 |
Note that you also need to use "unblock_sub" for any other callbacks |
| 382 |
that are indirectly executed by any C-based event loop. For example, |
| 383 |
when you use a module that uses AnyEvent (and you use |
| 384 |
Coro::AnyEvent) and it provides callbacks that are the result of |
| 385 |
some event callback, then you must not block either, or use |
| 386 |
"unblock_sub". |
| 387 |
|
| 388 |
BUGS/LIMITATIONS |
| 389 |
This module is not perl-pseudo-thread-safe. You should only ever use |
| 390 |
this module from the same thread (this requirement might be removed in |
| 391 |
the future to allow per-thread schedulers, but Coro::State does not yet |
| 392 |
allow this). I recommend disabling thread support and using processes, |
| 393 |
as this is much faster and uses less memory. |
| 394 |
|
| 395 |
SEE ALSO |
| 396 |
Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
| 397 |
|
| 398 |
Debugging: Coro::Debug. |
| 399 |
|
| 400 |
Support/Utility: Coro::Specific, Coro::Util. |
| 401 |
|
| 402 |
Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, |
| 403 |
Coro::SemaphoreSet, Coro::RWLock. |
| 404 |
|
| 405 |
IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO. |
| 406 |
|
| 407 |
Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select. |
| 408 |
|
| 409 |
XS API: Coro::MakeMaker. |
| 410 |
|
| 411 |
Low level Configuration, Coroutine Environment: Coro::State. |
| 412 |
|
| 413 |
AUTHOR |
| 414 |
Marc Lehmann <schmorp@schmorp.de> |
| 415 |
http://home.schmorp.de/ |
| 416 |
|
