NAME Coro - coroutine process abstraction SYNOPSIS use Coro; async { # some asynchronous thread of execution }; # alternatively create an async coroutine like this: sub some_func : Coro { # some more async code } cede; DESCRIPTION This module collection manages coroutines. Coroutines are similar to threads but don't run in parallel at the same time even on SMP machines. The specific flavor of coroutine use din this module also guarentees you that it will not switch between coroutines unless necessary, at easily-identified points in your program, so locking and parallel access are rarely an issue, making coroutine programming much safer than threads programming. (Perl, however, does not natively support real threads but instead does a very slow and memory-intensive emulation of processes using threads. This is a performance win on Windows machines, and a loss everywhere else). In this module, coroutines are defined as "callchain + lexical variables + @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own callchain, its own set of lexicals and its own set of perls most important global variables. $main This coroutine represents the main program. $current (or as function: current) The current coroutine (the last coroutine switched to). The initial value is $main (of course). This variable is strictly *read-only*. It is provided for performance reasons. If performance is not essentiel you are encouraged to use the "Coro::current" function instead. $idle A callback that is called whenever the scheduler finds no ready coroutines to run. The default implementation prints "FATAL: deadlock detected" and exits, because the program has no other way to continue. This hook is overwritten by modules such as "Coro::Timer" and "Coro::Event" to wait on an external event that hopefully wake up a coroutine so the scheduler can run it. Please note that if your callback recursively invokes perl (e.g. for event handlers), then it must be prepared to be called recursively. STATIC METHODS Static methods are actually functions that operate on the current coroutine only. async { ... } [@args...] Create a new asynchronous coroutine and return it's coroutine object (usually unused). When the sub returns the new coroutine is automatically terminated. Calling "exit" in a coroutine will not work correctly, so do not do that. When the coroutine dies, the program will exit, just as in the main program. # create a new coroutine that just prints its arguments async { print "@_\n"; } 1,2,3,4; schedule Calls the scheduler. Please note that the current coroutine will not be put into the ready queue, so calling this function usually means you will never be called again unless something else (e.g. an event handler) calls ready. The canonical way to wait on external events is this: { # remember current coroutine my $current = $Coro::current; # register a hypothetical event handler on_event_invoke sub { # wake up sleeping coroutine $current->ready; undef $current; }; # call schedule until event occured. # in case we are woken up for other reasons # (current still defined), loop. Coro::schedule while $current; } cede "Cede" to other coroutines. This function puts the current coroutine into the ready queue and calls "schedule", which has the effect of giving up the current "timeslice" to other coroutines of the same or higher priority. terminate [arg...] Terminates the current coroutine with the given status values (see cancel). # dynamic methods COROUTINE METHODS These are the methods you can call on coroutine objects. new Coro \&sub [, @args...] Create a new coroutine and return it. When the sub returns the coroutine automatically terminates as if "terminate" with the returned values were called. To make the coroutine run you must first put it into the ready queue by calling the ready method. Calling "exit" in a coroutine will not work correctly, so do not do that. $success = $coroutine->ready Put the given coroutine into the ready queue (according to it's priority) and return true. If the coroutine is already in the ready queue, do nothing and return false. $is_ready = $coroutine->is_ready Return wether the coroutine is currently the ready queue or not, $coroutine->cancel (arg...) Terminates the given coroutine and makes it return the given arguments as status (default: the empty list). $coroutine->join Wait until the coroutine terminates and return any values given to the "terminate" or "cancel" functions. "join" can be called multiple times from multiple coroutine. $oldprio = $coroutine->prio ($newprio) Sets (or gets, if the argument is missing) the priority of the coroutine. Higher priority coroutines get run before lower priority coroutines. Priorities are small signed integers (currently -4 .. +3), that you can refer to using PRIO_xxx constants (use the import tag :prio to get then): PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN 3 > 1 > 0 > -1 > -3 > -4 # set priority to HIGH current->prio(PRIO_HIGH); The idle coroutine ($Coro::idle) always has a lower priority than any existing coroutine. Changing the priority of the current coroutine will take effect immediately, but changing the priority of coroutines in the ready queue (but not running) will only take effect after the next schedule (of that coroutine). This is a bug that will be fixed in some future version. $newprio = $coroutine->nice ($change) Similar to "prio", but subtract the given value from the priority (i.e. higher values mean lower priority, just as in unix). $olddesc = $coroutine->desc ($newdesc) Sets (or gets in case the argument is missing) the description for this coroutine. This is just a free-form string you can associate with a coroutine. GLOBAL FUNCTIONS Coro::nready Returns the number of coroutines that are currently in the ready state, i.e. that can be swicthed to. The value 0 means that the only runnable coroutine is the currently running one, so "cede" would have no effect, and "schedule" would cause a deadlock unless there is an idle handler that wakes up some coroutines. unblock_sub { ... } This utility function takes a BLOCK or code reference and "unblocks" it, returning the new coderef. This means that the new coderef will return immediately without blocking, returning nothing, while the original code ref will be called (with parameters) from within its own coroutine. The reason this fucntion exists is that many event libraries (such as the venerable Event module) are not coroutine-safe (a weaker form of thread-safety). This means you must not block within event callbacks, otherwise you might suffer from crashes or worse. This function allows your callbacks to block by executing them in another coroutine where it is safe to block. One example where blocking is handy is when you use the Coro::AIO functions to save results to disk. In short: simply use "unblock_sub { ... }" instead of "sub { ... }" when creating event callbacks that want to block. BUGS/LIMITATIONS - you must make very sure that no coro is still active on global destruction. very bad things might happen otherwise (usually segfaults). - this module is not thread-safe. You should only ever use this module from the same thread (this requirement might be losened in the future to allow per-thread schedulers, but Coro::State does not yet allow this). SEE ALSO Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util. Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, Coro::SemaphoreSet, Coro::RWLock. Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket, Coro::Select. Embedding: AUTHOR Marc Lehmann http://home.schmorp.de/