--- Coro/README 2005/08/20 01:10:22 1.2 +++ Coro/README 2007/10/06 19:25:00 1.11 @@ -8,7 +8,7 @@ # some asynchronous thread of execution }; - # alternatively create an async process like this: + # alternatively create an async coroutine like this: sub some_func : Coro { # some more async code @@ -18,11 +18,21 @@ DESCRIPTION This module collection manages coroutines. Coroutines are similar to - threads but don't run in parallel. + threads but don't run in parallel at the same time even on SMP machines. + The specific flavor of coroutine used in this module also guarantees 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 - + @_ + $_ + $@ + $^W + C stack), that is, a coroutine has it's own - callchain, it's own set of lexicals and it's own set of perl's most + + @_ + $_ + $@ + $/ + 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 @@ -32,66 +42,163 @@ 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 essential you are + encouraged to use the "Coro::current" function instead. + $idle - The coroutine to switch to when no other coroutine is running. The - default implementation prints "FATAL: deadlock detected" and exits. + 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 - process only. + coroutine only. async { ... } [@args...] - Create a new asynchronous process and return it's process object - (usually unused). When the sub returns the new process is + Create a new asynchronous coroutine and return it's coroutine object + (usually unused). When the sub returns the new coroutine is automatically terminated. + See the "Coro::State::new" constructor for info about the coroutine + environment. + + Calling "exit" in a coroutine will do the same as calling exit + outside the coroutine. Likewise, when the coroutine dies, the + program will exit, just as it would in the main program. + # create a new coroutine that just prints its arguments async { print "@_\n"; } 1,2,3,4; + async_pool { ... } [@args...] + Similar to "async", but uses a coroutine pool, so you should not + call terminate or join (although you are allowed to), and you get a + coroutine that might have executed other code already (which can be + good or bad :). + + Also, the block is executed in an "eval" context and a warning will + be issued in case of an exception instead of terminating the + program, as "async" does. As the coroutine is being reused, stuff + like "on_destroy" will not work in the expected way, unless you call + terminate or cancel, which somehow defeats the purpose of pooling. + + The priority will be reset to 0 after each job, tracing will be + disabled, the description will be reset and the default output + filehandle gets restored, so you can change alkl these. Otherwise + the coroutine will be re-used "as-is": most notably if you change + other per-coroutine global stuff such as $/ you need to revert that + change, which is most simply done by using local as in " local $/ ". + + The pool size is limited to 8 idle coroutines (this can be adjusted + by changing $Coro::POOL_SIZE), and there can be as many non-idle + coros as required. + + If you are concerned about pooled coroutines growing a lot because a + single "async_pool" used a lot of stackspace you can e.g. + "async_pool { terminate }" once per second or so to slowly replenish + the pool. In addition to that, when the stacks used by a handler + grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will + also exit. + schedule - Calls the scheduler. Please note that the current process will not + 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. + 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 occurred. + # in case we are woken up for other reasons + # (current still defined), loop. + Coro::schedule while $current; + } cede - "Cede" to other processes. This function puts the current process + "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. + Returns true if at least one coroutine switch has happened. + + Coro::cede_notself + Works like cede, but is not exported by default and will cede to any + coroutine, regardless of priority, once. + + Returns true if at least one coroutine switch has happened. + terminate [arg...] - Terminates the current process with the given status values (see + Terminates the current coroutine with the given status values (see cancel). + killall + Kills/terminates/cancels all coroutines except the currently running + one. This is useful after a fork, either in the child or the parent, + as usually only one of them should inherit the running coroutines. + # dynamic methods - PROCESS METHODS - These are the methods you can call on process objects. + COROUTINE METHODS + These are the methods you can call on coroutine objects. new Coro \&sub [, @args...] - Create a new process and return it. When the sub returns the process - automatically terminates as if "terminate" with the returned values - were called. To make the process run you must first put it into the - ready queue by calling the ready method. - - $process->ready - Put the given process into the ready queue. - - $process->cancel (arg...) - Temrinates the given process and makes it return the given arguments - as status (default: the empty list). + 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. + + See "async" and "Coro::State::new" for additional info about the + coroutine environment. + + $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). Never returns if the + coroutine is the current coroutine. - $process->join + $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 processes. + the "terminate" or "cancel" functions. "join" can be called + concurrently from multiple coroutines. + + $coroutine->on_destroy (\&cb) + Registers a callback that is called when this coroutine gets + destroyed, but before it is joined. The callback gets passed the + terminate arguments, if any. - $oldprio = $process->prio($newprio) + $oldprio = $coroutine->prio ($newprio) Sets (or gets, if the argument is missing) the priority of the - process. Higher priority processes get run before lower priority - processes. Priorities are small signed integers (currently -4 .. + 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): @@ -104,32 +211,97 @@ The idle coroutine ($Coro::idle) always has a lower priority than any existing coroutine. - Changing the priority of the current process will take effect - immediately, but changing the priority of processes in the ready + 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 process). This is a bug that will be fixed in some - future version. + schedule (of that coroutine). This is a bug that will be fixed in + some future version. - $newprio = $process->nice($change) + $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 = $process->desc($newdesc) + $olddesc = $coroutine->desc ($newdesc) Sets (or gets in case the argument is missing) the description for - this process. This is just a free-form string you can associate with - a process. + this coroutine. This is just a free-form string you can associate + with a coroutine. + + This method simply sets the "$coroutine->{desc}" member to the given + string. You can modify this member directly if you wish. + + $coroutine->throw ([$scalar]) + If $throw is specified and defined, it will be thrown as an + exception inside the coroutine at the next convinient point in time + (usually after it gains control at the next schedule/transfer/cede). + Otherwise clears the exception object. + + The exception object will be thrown "as is" with the specified + scalar in $@, i.e. if it is a string, no line number or newline will + be appended (unlike with "die"). + + This can be used as a softer means than "cancel" to ask a coroutine + to end itself, although there is no guarentee that the exception + will lead to termination, and if the exception isn't caught it might + well end the whole program. + + GLOBAL FUNCTIONS + Coro::nready + Returns the number of coroutines that are currently in the ready + state, i.e. that can be switched 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. + + my $guard = Coro::guard { ... } + This creates and returns a guard object. Nothing happens until the + object gets destroyed, in which case the codeblock given as argument + will be executed. This is useful to free locks or other resources in + case of a runtime error or when the coroutine gets canceled, as in + both cases the guard block will be executed. The guard object + supports only one method, "->cancel", which will keep the codeblock + from being executed. + + Example: set some flag and clear it again when the coroutine gets + canceled or the function returns: + + sub do_something { + my $guard = Coro::guard { $busy = 0 }; + $busy = 1; + + # do something that requires $busy to be true + } + + 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 function 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 + from the same thread (this requirement might be loosened 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. + Support/Utility: Coro::Specific, Coro::State, Coro::Util. Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, Coro::SemaphoreSet, Coro::RWLock.