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NAME |
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Coro - coroutine process abstraction |
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SYNOPSIS |
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use Coro; |
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async { |
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# some asynchronous thread of execution |
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}; |
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# alternatively create an async coroutine like this: |
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sub some_func : Coro { |
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# some more async code |
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} |
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cede; |
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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 run in parallel at the same time even on SMP machines. |
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The specific flavor of coroutine used in this module also guarantees you |
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that it will not switch between coroutines 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 coroutine programming much safer than |
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threads programming. |
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(Perl, however, does not natively support real threads but instead does |
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a very slow and memory-intensive emulation of processes using threads. |
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This is a performance win on Windows machines, and a loss everywhere |
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else). |
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In this module, coroutines are defined as "callchain + lexical variables |
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+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own |
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callchain, its own set of lexicals and its own set of perls most |
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important global variables. |
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$main |
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This coroutine represents the main program. |
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$current (or as function: current) |
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The current coroutine (the last coroutine switched to). The initial |
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value is $main (of course). |
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This variable is strictly *read-only*. It is provided for |
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performance reasons. If performance is not essential you are |
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encouraged to use the "Coro::current" function instead. |
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$idle |
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A callback that is called whenever the scheduler finds no ready |
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coroutines 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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This hook is overwritten by modules such as "Coro::Timer" and |
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"Coro::Event" to wait on an external event that hopefully wake up a |
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coroutine so the scheduler can run it. |
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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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STATIC METHODS |
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Static methods are actually functions that operate on the current |
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coroutine only. |
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async { ... } [@args...] |
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Create a new asynchronous coroutine and return it's coroutine object |
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(usually unused). When the sub returns the new coroutine is |
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automatically terminated. |
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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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# create a new coroutine that just prints its arguments |
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async { |
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print "@_\n"; |
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} 1,2,3,4; |
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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 (although you are allowed to), and you get a |
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coroutine that might have executed other code already (which can be |
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good or bad :). |
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Also, the 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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The priority will be reset to 0 after each job, otherwise the |
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coroutine will be re-used "as-is". |
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The pool size is limited to 8 idle coroutines (this can be adjusted |
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by changing $Coro::POOL_SIZE), and there can be as many non-idle |
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coros as required. |
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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. |
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schedule |
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Calls the scheduler. Please note that the current coroutine will not |
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be put into the ready queue, so calling this function usually means |
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you will never be called again unless something else (e.g. an event |
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handler) calls ready. |
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The canonical way to wait on external events is this: |
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{ |
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# remember current coroutine |
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my $current = $Coro::current; |
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# register a hypothetical event handler |
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on_event_invoke sub { |
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# wake up sleeping coroutine |
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$current->ready; |
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undef $current; |
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}; |
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# 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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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. |
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Returns true if at least one coroutine switch has happened. |
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Coro::cede_notself |
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Works like cede, but is not exported by default and will cede to any |
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coroutine, regardless of priority, once. |
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Returns true if at least one coroutine switch has happened. |
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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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# dynamic methods |
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COROUTINE METHODS |
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These are the methods you can call on coroutine objects. |
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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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See "async" for additional discussion. |
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$success = $coroutine->ready |
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Put the given coroutine into the ready queue (according to it's |
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priority) and return true. If the coroutine is already in the ready |
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queue, do nothing and return false. |
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$is_ready = $coroutine->is_ready |
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Return wether the coroutine is currently the ready queue or not, |
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$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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$coroutine->join |
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Wait until the coroutine terminates and return any values given to |
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the "terminate" or "cancel" functions. "join" can be called multiple |
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times from multiple coroutine. |
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$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. |
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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 |
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coroutines. Priorities are small signed integers (currently -4 .. |
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+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 ($Coro::idle) always has a lower priority than |
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any existing coroutine. |
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Changing the priority of the current coroutine will take effect |
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immediately, but changing the priority of coroutines in the ready |
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queue (but not running) will only take effect after the next |
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schedule (of that coroutine). This is a bug that will be fixed in |
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some future version. |
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$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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$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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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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state, i.e. that can be switched to. The value 0 means that the only |
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runnable coroutine is the currently running one, so "cede" would |
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have no effect, and "schedule" would cause a deadlock unless there |
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is an idle handler that wakes up some coroutines. |
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my $guard = Coro::guard { ... } |
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This creates and returns a guard object. Nothing happens until the |
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object gets destroyed, in which case the codeblock given as argument |
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will be executed. This is useful to free locks or other resources in |
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case of a runtime error or when the coroutine gets canceled, as in |
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both cases the guard block will be executed. The guard object |
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supports only one method, "->cancel", which will keep the codeblock |
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from being executed. |
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Example: set some flag and clear it again when the coroutine gets |
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canceled or the function returns: |
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sub do_something { |
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my $guard = Coro::guard { $busy = 0 }; |
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$busy = 1; |
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# do something that requires $busy to be true |
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} |
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unblock_sub { ... } |
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This utility function takes a BLOCK or code reference and "unblocks" |
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it, returning the new coderef. This means that the new coderef will |
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return immediately without blocking, returning nothing, while the |
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original code ref will be called (with parameters) from within its |
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own coroutine. |
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The reason this function exists is that many event libraries (such |
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as the venerable Event module) are not coroutine-safe (a weaker form |
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of thread-safety). This means you must not block within event |
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callbacks, otherwise you might suffer from crashes or worse. |
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This function allows your callbacks to block by executing them in |
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another coroutine where it is safe to block. One example where |
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blocking is handy is when you use the Coro::AIO functions to save |
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results to disk. |
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In short: simply use "unblock_sub { ... }" instead of "sub { ... }" |
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when creating event callbacks that want to block. |
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BUGS/LIMITATIONS |
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- you must make very sure that no coro is still active on global |
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destruction. very bad things might happen otherwise (usually segfaults). |
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- this module is not thread-safe. You should only ever use this module |
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from the same thread (this requirement might be loosened in the future |
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to allow per-thread schedulers, but Coro::State does not yet allow |
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this). |
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SEE ALSO |
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Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util. |
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Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, |
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Coro::SemaphoreSet, Coro::RWLock. |
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Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket, |
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Coro::Select. |
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Embedding: <Coro:MakeMaker> |
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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