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Revision 1.2 by root, Sat Aug 20 01:10:22 2005 UTC vs.
Revision 1.17 by root, Wed Nov 5 15:38:10 2008 UTC

…		…
1	NAME	1	NAME
2	Coro - coroutine process abstraction	2	Coro - coroutine process abstraction
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use Coro;	5	use Coro;
6		6
7	async {	7	async {
8	# some asynchronous thread of execution	8	# some asynchronous thread of execution
		9	print "2\n";
		10	cede; # yield back to main
		11	print "4\n";
9	};	12	};
10		13	print "1\n";
11	# alternatively create an async process like this:	14	cede; # yield to coroutine
12		15	print "3\n";
13	sub some_func : Coro {	16	cede; # and again
14	# some more async code
15	}	17
16		18	# use locking
17	cede;	19	use Coro::Semaphore;
		20	my $lock = new Coro::Semaphore;
		21	my $locked;
		22
		23	$lock->down;
		24	$locked = 1;
		25	$lock->up;
18		26
19	DESCRIPTION	27	DESCRIPTION
20	This module collection manages coroutines. Coroutines are similar to	28	This module collection manages coroutines. Coroutines are similar to
21	threads but don't run in parallel.	29	threads but don't (in general) run in parallel at the same time even on
		30	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.
		35
		36	Unlike a normal perl program, however, coroutines allow you to have
		37	multiple running interpreters that share data, which is especially
		38	useful to code pseudo-parallel processes and for event-based
		39	programming, such as multiple HTTP-GET requests running concurrently.
		40	See Coro::AnyEvent to learn more.
		41
		42	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).
22		49
23	In this module, coroutines are defined as "callchain + lexical variables	50	In this module, coroutines are defined as "callchain + lexical variables
24	+ @_ + $_ + $@ + $^W + C stack), that is, a coroutine has it's own	51	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
25	callchain, it's own set of lexicals and it's own set of perl's most	52	callchain, its own set of lexicals and its own set of perls most
26	important global variables.	53	important global variables (see Coro::State for more configuration).
27		54
28	$main	55	$Coro::main
29	This coroutine represents the main program.	56	This variable stores the coroutine object that represents the main
		57	program. While you cna "ready" it and do most other things you can
		58	do to coroutines, it is mainly useful to compare again
		59	$Coro::current, to see whether you are running in the main program
		60	or not.
30		61
31	$current (or as function: current)	62	$Coro::current
32	The current coroutine (the last coroutine switched to). The initial	63	The coroutine object representing the current coroutine (the last
		64	coroutine that the Coro scheduler switched to). The initial value is
33	value is $main (of course).	65	$main (of course).
34		66
		67	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
		69	must not otherwise modify the variable itself.
		70
35	$idle	71	$Coro::idle
36	The coroutine to switch to when no other coroutine is running. The	72	This variable is mainly useful to integrate Coro into event loops.
		73	It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as
		74	this is pretty low-level functionality.
		75
		76	This variable stores a callback that is called whenever the
		77	scheduler finds no ready coroutines to run. The default
37	default implementation prints "FATAL: deadlock detected" and exits.	78	implementation prints "FATAL: deadlock detected" and exits, because
		79	the program has no other way to continue.
38		80
39	STATIC METHODS	81	This hook is overwritten by modules such as "Coro::Timer" and
40	Static methods are actually functions that operate on the current	82	"Coro::AnyEvent" to wait on an external event that hopefully wake up
41	process only.	83	a coroutine so the scheduler can run it.
42		84
		85	Note that the callback must not, under any circumstances, block
		86	the current coroutine. Normally, this is achieved by having an "idle
		87	coroutine" that calls the event loop and then blocks again, and then
		88	readying that coroutine in the idle handler.
		89
		90	See Coro::Event or Coro::AnyEvent for examples of using this
		91	technique.
		92
		93	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.
		96
		97	SIMPLE COROUTINE CREATION
43	async { ... } [@args...]	98	async { ... } [@args...]
44	Create a new asynchronous process and return it's process object	99	Create a new coroutine and return it's coroutine object (usually
45	(usually unused). When the sub returns the new process is	100	unused). The coroutine will be put into the ready queue, so it will
		101	start running automatically on the next scheduler run.
		102
		103	The first argument is a codeblock/closure that should be executed in
		104	the coroutine. When it returns argument returns the coroutine is
46	automatically terminated.	105	automatically terminated.
47		106
		107	The remaining arguments are passed as arguments to the closure.
		108
		109	See the "Coro::State::new" constructor for info about the coroutine
		110	environment in which coroutines are executed.
		111
		112	Calling "exit" in a coroutine will do the same as calling exit
		113	outside the coroutine. Likewise, when the coroutine dies, the
		114	program will exit, just as it would in the main program.
		115
		116	If you do not want that, you can provide a default "die" handler, or
		117	simply avoid dieing (by use of "eval").
		118
48	# create a new coroutine that just prints its arguments	119	Example: Create a new coroutine that just prints its arguments.
		120
49	async {	121	async {
50	print "@_\n";	122	print "@_\n";
51	} 1,2,3,4;	123	} 1,2,3,4;
52		124
		125	async_pool { ... } [@args...]
		126	Similar to "async", but uses a coroutine pool, so you should not
		127	call terminate or join on it (although you are allowed to), and you
		128	get a coroutine that might have executed other code already (which
		129	can be good or bad :).
		130
		131	On the plus side, this function is faster than creating (and
		132	destroying) a completly new coroutine, so if you need a lot of
		133	generic coroutines in quick successsion, use "async_pool", not
		134	"async".
		135
		136	The code block is executed in an "eval" context and a warning will
		137	be issued in case of an exception instead of terminating the
		138	program, as "async" does. As the coroutine is being reused, stuff
		139	like "on_destroy" will not work in the expected way, unless you call
		140	terminate or cancel, which somehow defeats the purpose of pooling
		141	(but is fine in the exceptional case).
		142
		143	The priority will be reset to 0 after each run, tracing will be
		144	disabled, the description will be reset and the default output
		145	filehandle gets restored, so you can change all these. Otherwise the
		146	coroutine will be re-used "as-is": most notably if you change other
		147	per-coroutine global stuff such as $/ you must needs revert that
		148	change, which is most simply done by using local as in: "local $/".
		149
		150	The idle pool size is limited to 8 idle coroutines (this can be
		151	adjusted by changing $Coro::POOL_SIZE), but there can be as many
		152	non-idle coros as required.
		153
		154	If you are concerned about pooled coroutines growing a lot because a
		155	single "async_pool" used a lot of stackspace you can e.g.
		156	"async_pool { terminate }" once per second or so to slowly replenish
		157	the pool. In addition to that, when the stacks used by a handler
		158	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also
		159	be destroyed.
		160
		161	STATIC METHODS
		162	Static methods are actually functions that operate on the current
		163	coroutine.
		164
53	schedule	165	schedule
54	Calls the scheduler. Please note that the current process will not	166	Calls the scheduler. The scheduler will find the next coroutine that
		167	is to be run from the ready queue and switches to it. The next
		168	coroutine to be run is simply the one with the highest priority that
		169	is longest in its ready queue. If there is no coroutine ready, it
		170	will clal the $Coro::idle hook.
		171
		172	Please note that the current coroutine will not be put into the
55	be put into the ready queue, so calling this function usually means	173	ready queue, so calling this function usually means you will never
56	you will never be called again.	174	be called again unless something else (e.g. an event handler) calls
		175	"->ready", thus waking you up.
		176
		177	This makes "schedule" the generic method to use to block the
		178	current coroutine and wait for events: first you remember the
		179	current coroutine in a variable, then arrange for some callback of
		180	yours to call "->ready" on that once some event happens, and last
		181	you call "schedule" to put yourself to sleep. Note that a lot of
		182	things can wake your coroutine up, so you need to check whether the
		183	event indeed happened, e.g. by storing the status in a variable.
		184
		185	The canonical way to wait on external events is this:
		186
		187	{
		188	# remember current coroutine
		189	my $current = $Coro::current;
		190
		191	# register a hypothetical event handler
		192	on_event_invoke sub {
		193	# wake up sleeping coroutine
		194	$current->ready;
		195	undef $current;
		196	};
		197
		198	# call schedule until event occurred.
		199	# in case we are woken up for other reasons
		200	# (current still defined), loop.
		201	Coro::schedule while $current;
		202	}
57		203
58	cede	204	cede
59	"Cede" to other processes. This function puts the current process	205	"Cede" to other coroutines. This function puts the current coroutine
60	into the ready queue and calls "schedule", which has the effect of	206	into the ready queue and calls "schedule", which has the effect of
61	giving up the current "timeslice" to other coroutines of the same or	207	giving up the current "timeslice" to other coroutines of the same or
62	higher priority.	208	higher priority. Once your coroutine gets its turn again it will
		209	automatically be resumed.
		210
		211	This function is often called "yield" in other languages.
		212
		213	Coro::cede_notself
		214	Works like cede, but is not exported by default and will cede to
		215	any coroutine, regardless of priority. This is useful sometimes to
		216	ensure progress is made.
63		217
64	terminate [arg...]	218	terminate [arg...]
65	Terminates the current process with the given status values (see	219	Terminates the current coroutine with the given status values (see
66	cancel).	220	cancel).
67		221
68	# dynamic methods	222	killall
		223	Kills/terminates/cancels all coroutines except the currently running
		224	one. This is useful after a fork, either in the child or the parent,
		225	as usually only one of them should inherit the running coroutines.
69		226
70	PROCESS METHODS	227	Note that while this will try to free some of the main programs
		228	resources, you cannot free all of them, so if a coroutine that is
		229	not the main program calls this function, there will be some
		230	one-time resource leak.
		231
		232	COROUTINE METHODS
71	These are the methods you can call on process objects.	233	These are the methods you can call on coroutine objects (or to create
		234	them).
72		235
73	new Coro \&sub [, @args...]	236	new Coro \&sub [, @args...]
74	Create a new process and return it. When the sub returns the process	237	Create a new coroutine and return it. When the sub returns, the
75	automatically terminates as if "terminate" with the returned values	238	coroutine automatically terminates as if "terminate" with the
76	were called. To make the process run you must first put it into the	239	returned values were called. To make the coroutine run you must
77	ready queue by calling the ready method.	240	first put it into the ready queue by calling the ready method.
78		241
79	$process->ready	242	See "async" and "Coro::State::new" for additional info about the
80	Put the given process into the ready queue.	243	coroutine environment.
81		244
		245	$success = $coroutine->ready
		246	Put the given coroutine into the end of its ready queue (there is
		247	one queue for each priority) and return true. If the coroutine is
		248	already in the ready queue, do nothing and return false.
		249
		250	This ensures that the scheduler will resume this coroutine
		251	automatically once all the coroutines of higher priority and all
		252	coroutines of the same priority that were put into the ready queue
		253	earlier have been resumed.
		254
		255	$is_ready = $coroutine->is_ready
		256	Return whether the coroutine is currently the ready queue or not,
		257
82	$process->cancel (arg...)	258	$coroutine->cancel (arg...)
83	Temrinates the given process and makes it return the given arguments	259	Terminates the given coroutine and makes it return the given
84	as status (default: the empty list).	260	arguments as status (default: the empty list). Never returns if the
		261	coroutine is the current coroutine.
85		262
86	$process->join	263	$coroutine->throw ([$scalar])
		264	If $throw is specified and defined, it will be thrown as an
		265	exception inside the coroutine at the next convenient point in time
		266	(usually after it gains control at the next schedule/transfer/cede).
		267	Otherwise clears the exception object.
		268
		269	The exception object will be thrown "as is" with the specified
		270	scalar in $@, i.e. if it is a string, no line number or newline will
		271	be appended (unlike with "die").
		272
		273	This can be used as a softer means than "cancel" to ask a coroutine
		274	to end itself, although there is no guarantee that the exception
		275	will lead to termination, and if the exception isn't caught it might
		276	well end the whole program.
		277
		278	You might also think of "throw" as being the moral equivalent of
		279	"kill"ing a coroutine with a signal (in this case, a scalar).
		280
		281	$coroutine->join
87	Wait until the coroutine terminates and return any values given to	282	Wait until the coroutine terminates and return any values given to
88	the "terminate" or "cancel" functions. "join" can be called multiple	283	the "terminate" or "cancel" functions. "join" can be called
89	times from multiple processes.	284	concurrently from multiple coroutines, and all will be resumed and
		285	given the status return once the $coroutine terminates.
90		286
		287	$coroutine->on_destroy (\&cb)
		288	Registers a callback that is called when this coroutine gets
		289	destroyed, but before it is joined. The callback gets passed the
		290	terminate arguments, if any, and must not die, under any
		291	circumstances.
		292
91	$oldprio = $process->prio($newprio)	293	$oldprio = $coroutine->prio ($newprio)
92	Sets (or gets, if the argument is missing) the priority of the	294	Sets (or gets, if the argument is missing) the priority of the
93	process. Higher priority processes get run before lower priority	295	coroutine. Higher priority coroutines get run before lower priority
94	processes. Priorities are small signed integers (currently -4 ..	296	coroutines. Priorities are small signed integers (currently -4 ..
95	+3), that you can refer to using PRIO_xxx constants (use the import	297	+3), that you can refer to using PRIO_xxx constants (use the import
96	tag :prio to get then):	298	tag :prio to get then):
97		299
98	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN	300	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
99	3 > 1 > 0 > -1 > -3 > -4	301	3 > 1 > 0 > -1 > -3 > -4
102	current->prio(PRIO_HIGH);	304	current->prio(PRIO_HIGH);
103		305
104	The idle coroutine ($Coro::idle) always has a lower priority than	306	The idle coroutine ($Coro::idle) always has a lower priority than
105	any existing coroutine.	307	any existing coroutine.
106		308
107	Changing the priority of the current process will take effect	309	Changing the priority of the current coroutine will take effect
108	immediately, but changing the priority of processes in the ready	310	immediately, but changing the priority of coroutines in the ready
109	queue (but not running) will only take effect after the next	311	queue (but not running) will only take effect after the next
110	schedule (of that process). This is a bug that will be fixed in some	312	schedule (of that coroutine). This is a bug that will be fixed in
111	future version.	313	some future version.
112		314
113	$newprio = $process->nice($change)	315	$newprio = $coroutine->nice ($change)
114	Similar to "prio", but subtract the given value from the priority	316	Similar to "prio", but subtract the given value from the priority
115	(i.e. higher values mean lower priority, just as in unix).	317	(i.e. higher values mean lower priority, just as in unix).
116		318
117	$olddesc = $process->desc($newdesc)	319	$olddesc = $coroutine->desc ($newdesc)
118	Sets (or gets in case the argument is missing) the description for	320	Sets (or gets in case the argument is missing) the description for
119	this process. This is just a free-form string you can associate with	321	this coroutine. This is just a free-form string you can associate
120	a process.	322	with a coroutine.
		323
		324	This method simply sets the "$coroutine->{desc}" member to the given
		325	string. You can modify this member directly if you wish.
		326
		327	GLOBAL FUNCTIONS
		328	Coro::nready
		329	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.
		335
		336	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.
		344
		345	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".
121		387
122	BUGS/LIMITATIONS	388	BUGS/LIMITATIONS
123	- you must make very sure that no coro is still active on global
124	destruction. very bad things might happen otherwise (usually segfaults).
125
126	- this module is not thread-safe. You should only ever use this module	389	This module is not perl-pseudo-thread-safe. You should only ever use
127	from the same thread (this requirement might be losened in the future	390	this module from the same thread (this requirement might be removed in
128	to allow per-thread schedulers, but Coro::State does not yet allow	391	the future to allow per-thread schedulers, but Coro::State does not yet
129	this).	392	allow this). I recommend disabling thread support and using processes,
		393	as this is much faster and uses less memory.
130		394
131	SEE ALSO	395	SEE ALSO
		396	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
		397
		398	Debugging: Coro::Debug.
		399
132	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.	400	Support/Utility: Coro::Specific, Coro::Util.
133		401
134	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	402	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
135	Coro::SemaphoreSet, Coro::RWLock.	403	Coro::SemaphoreSet, Coro::RWLock.
136		404
137	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,	405	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
138	Coro::Select.
139		406
140	Embedding: <Coro:MakeMaker>	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.
141		412
142	AUTHOR	413	AUTHOR
143	Marc Lehmann <schmorp@schmorp.de>	414	Marc Lehmann <schmorp@schmorp.de>
144	http://home.schmorp.de/	415	http://home.schmorp.de/
145		416

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Comparing Coro/README (file contents): Revision 1.2 by root, Sat Aug 20 01:10:22 2005 UTC vs. Revision 1.17 by root, Wed Nov 5 15:38:10 2008 UTC

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Comparing Coro/README (file contents):
Revision 1.2 by root, Sat Aug 20 01:10:22 2005 UTC vs.
Revision 1.17 by root, Wed Nov 5 15:38:10 2008 UTC