[ViewVC] Diff of: cvs/Coro/README

Comparing Coro/README (file contents):
Revision 1.12 by root, Thu Oct 11 00:38:37 2007 UTC vs.
Revision 1.15 by root, Sun Sep 21 01:23:26 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";	9	print "2\n";
10	cede; # yield back to main	10	cede; # yield back to main
11	print "4\n";	11	print "4\n";
12	};	12	};
13	print "1\n";	13	print "1\n";
14	cede; # yield to coroutine	14	cede; # yield to coroutine
15	print "3\n";	15	print "3\n";
16	cede; # and again	16	cede; # and again
17		17
18	# use locking	18	# use locking
		19	use Coro::Semaphore;
19	my $lock = new Coro::Semaphore;	20	my $lock = new Coro::Semaphore;
20	my $locked;	21	my $locked;
21		22
22	$lock->down;	23	$lock->down;
23	$locked = 1;	24	$locked = 1;
24	$lock->up;	25	$lock->up;
25		26
26	DESCRIPTION	27	DESCRIPTION
27	This module collection manages coroutines. Coroutines are similar to	28	This module collection manages coroutines. Coroutines are similar to
28	threads but don't run in parallel at the same time even on SMP machines.	29	threads but don't (in general) run in parallel at the same time even on
29	The specific flavor of coroutine used in this module also guarantees you	30	SMP machines. The specific flavor of coroutine used in this module also
30	that it will not switch between coroutines unless necessary, at	31	guarantees you that it will not switch between coroutines unless
31	easily-identified points in your program, so locking and parallel access	32	necessary, at easily-identified points in your program, so locking and
32	are rarely an issue, making coroutine programming much safer than	33	parallel access are rarely an issue, making coroutine programming much
33	threads programming.	34	safer and easier than threads programming.
34		35
35	(Perl, however, does not natively support real threads but instead does	36	Unlike a normal perl program, however, coroutines allow you to have
36	a very slow and memory-intensive emulation of processes using threads.	37	multiple running interpreters that share data, which is especially
37	This is a performance win on Windows machines, and a loss everywhere	38	useful to code pseudo-parallel processes and for event-based
38	else).	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).
39		49
40	In this module, coroutines are defined as "callchain + lexical variables	50	In this module, coroutines are defined as "callchain + lexical variables
41	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	51	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
42	callchain, its own set of lexicals and its own set of perls most	52	callchain, its own set of lexicals and its own set of perls most
43	important global variables (see Coro::State for more configuration).	53	important global variables (see Coro::State for more configuration).
44		54
45	$main	55	$Coro::main
46	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.
47		61
48	$current (or as function: current)	62	$Coro::current
49	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
50	value is $main (of course).	65	$main (of course).
51		66
52	This variable is strictly read-only. It is provided for	67	This variable is strictly read-only. You can take copies of the
53	performance reasons. If performance is not essential you are	68	value stored in it and use it as any other coroutine object, but you
54	encouraged to use the "Coro::current" function instead.	69	must not otherwise modify the variable itself.
55		70
56	$idle	71	$Coro::idle
57	A callback that is called whenever the scheduler finds no ready	72	This variable is mainly useful to integrate Coro into event loops.
58	coroutines to run. The default implementation prints "FATAL:	73	It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as
59	deadlock detected" and exits, because the program has no other way	74	this is pretty low-level functionality.
60	to continue.	75
		76	This variable stores a callback that is called whenever the
		77	scheduler finds no ready coroutines to run. The default
		78	implementation prints "FATAL: deadlock detected" and exits, because
		79	the program has no other way to continue.
61		80
62	This hook is overwritten by modules such as "Coro::Timer" and	81	This hook is overwritten by modules such as "Coro::Timer" and
63	"Coro::Event" to wait on an external event that hopefully wake up a	82	"Coro::AnyEvent" to wait on an external event that hopefully wake up
64	coroutine so the scheduler can run it.	83	a coroutine so the scheduler can run it.
		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.
65		92
66	Please note that if your callback recursively invokes perl (e.g. for	93	Please note that if your callback recursively invokes perl (e.g. for
67	event handlers), then it must be prepared to be called recursively	94	event handlers), then it must be prepared to be called recursively
68	itself.	95	itself.
69		96
70	STATIC METHODS	97	SIMPLE COROUTINE CREATION
71	Static methods are actually functions that operate on the current
72	coroutine only.
73
74	async { ... } [@args...]	98	async { ... } [@args...]
75	Create a new asynchronous coroutine and return it's coroutine object	99	Create a new coroutine and return it's coroutine object (usually
76	(usually unused). When the sub returns the new coroutine 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
77	automatically terminated.	105	automatically terminated.
78		106
		107	The remaining arguments are passed as arguments to the closure.
		108
79	See the "Coro::State::new" constructor for info about the coroutine	109	See the "Coro::State::new" constructor for info about the coroutine
80	environment in which coroutines run.	110	environment in which coroutines are executed.
81		111
82	Calling "exit" in a coroutine will do the same as calling exit	112	Calling "exit" in a coroutine will do the same as calling exit
83	outside the coroutine. Likewise, when the coroutine dies, the	113	outside the coroutine. Likewise, when the coroutine dies, the
84	program will exit, just as it would in the main program.	114	program will exit, just as it would in the main program.
85		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
86	# create a new coroutine that just prints its arguments	119	Example: Create a new coroutine that just prints its arguments.
		120
87	async {	121	async {
88	print "@_\n";	122	print "@_\n";
89	} 1,2,3,4;	123	} 1,2,3,4;
90		124
91	async_pool { ... } [@args...]	125	async_pool { ... } [@args...]
92	Similar to "async", but uses a coroutine pool, so you should not	126	Similar to "async", but uses a coroutine pool, so you should not
93	call terminate or join (although you are allowed to), and you get a	127	call terminate or join on it (although you are allowed to), and you
94	coroutine that might have executed other code already (which can be	128	get a coroutine that might have executed other code already (which
95	good or bad :).	129	can be good or bad :).
96		130
		131	On the plus side, this function is faster than creating (and
		132	destroying) a completely new coroutine, so if you need a lot of
		133	generic coroutines in quick successsion, use "async_pool", not
		134	"async".
		135
97	Also, the block is executed in an "eval" context and a warning will	136	The code block is executed in an "eval" context and a warning will
98	be issued in case of an exception instead of terminating the	137	be issued in case of an exception instead of terminating the
99	program, as "async" does. As the coroutine is being reused, stuff	138	program, as "async" does. As the coroutine is being reused, stuff
100	like "on_destroy" will not work in the expected way, unless you call	139	like "on_destroy" will not work in the expected way, unless you call
101	terminate or cancel, which somehow defeats the purpose of pooling.	140	terminate or cancel, which somehow defeats the purpose of pooling
		141	(but is fine in the exceptional case).
102		142
103	The priority will be reset to 0 after each job, tracing will be	143	The priority will be reset to 0 after each run, tracing will be
104	disabled, the description will be reset and the default output	144	disabled, the description will be reset and the default output
105	filehandle gets restored, so you can change alkl these. Otherwise	145	filehandle gets restored, so you can change all these. Otherwise the
106	the coroutine will be re-used "as-is": most notably if you change	146	coroutine will be re-used "as-is": most notably if you change other
107	other per-coroutine global stuff such as $/ you need to revert that	147	per-coroutine global stuff such as $/ you must needs to revert
108	change, which is most simply done by using local as in " local $/ ".	148	that change, which is most simply done by using local as in: " local
		149	$/ ".
109		150
110	The pool size is limited to 8 idle coroutines (this can be adjusted	151	The pool size is limited to 8 idle coroutines (this can be adjusted
111	by changing $Coro::POOL_SIZE), and there can be as many non-idle	152	by changing $Coro::POOL_SIZE), and there can be as many non-idle
112	coros as required.	153	coros as required.
113		154
114	If you are concerned about pooled coroutines growing a lot because a	155	If you are concerned about pooled coroutines growing a lot because a
115	single "async_pool" used a lot of stackspace you can e.g.	156	single "async_pool" used a lot of stackspace you can e.g.
116	"async_pool { terminate }" once per second or so to slowly replenish	157	"async_pool { terminate }" once per second or so to slowly replenish
117	the pool. In addition to that, when the stacks used by a handler	158	the pool. In addition to that, when the stacks used by a handler
118	grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will	159	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also
119	also exit.	160	be destroyed.
		161
		162	STATIC METHODS
		163	Static methods are actually functions that operate on the current
		164	coroutine.
120		165
121	schedule	166	schedule
122	Calls the scheduler. Please note that the current coroutine will not	167	Calls the scheduler. The scheduler will find the next coroutine that
		168	is to be run from the ready queue and switches to it. The next
		169	coroutine to be run is simply the one with the highest priority that
		170	is longest in its ready queue. If there is no coroutine ready, it
		171	will clal the $Coro::idle hook.
		172
		173	Please note that the current coroutine will not be put into the
123	be put into the ready queue, so calling this function usually means	174	ready queue, so calling this function usually means you will never
124	you will never be called again unless something else (e.g. an event	175	be called again unless something else (e.g. an event handler) calls
125	handler) calls ready.	176	"->ready", thus waking you up.
		177
		178	This makes "schedule" the generic method to use to block the
		179	current coroutine and wait for events: first you remember the
		180	current coroutine in a variable, then arrange for some callback of
		181	yours to call "->ready" on that once some event happens, and last
		182	you call "schedule" to put yourself to sleep. Note that a lot of
		183	things can wake your coroutine up, so you need to check whether the
		184	event indeed happened, e.g. by storing the status in a variable.
126		185
127	The canonical way to wait on external events is this:	186	The canonical way to wait on external events is this:
128		187
129	{	188	{
130	# remember current coroutine	189	# remember current coroutine
145		204
146	cede	205	cede
147	"Cede" to other coroutines. This function puts the current coroutine	206	"Cede" to other coroutines. This function puts the current coroutine
148	into the ready queue and calls "schedule", which has the effect of	207	into the ready queue and calls "schedule", which has the effect of
149	giving up the current "timeslice" to other coroutines of the same or	208	giving up the current "timeslice" to other coroutines of the same or
150	higher priority.	209	higher priority. Once your coroutine gets its turn again it will
		210	automatically be resumed.
		211
		212	This function is often called "yield" in other languages.
151		213
152	Coro::cede_notself	214	Coro::cede_notself
153	Works like cede, but is not exported by default and will cede to any	215	Works like cede, but is not exported by default and will cede to
154	coroutine, regardless of priority, once.	216	any coroutine, regardless of priority. This is useful sometimes to
		217	ensure progress is made.
155		218
156	terminate [arg...]	219	terminate [arg...]
157	Terminates the current coroutine with the given status values (see	220	Terminates the current coroutine with the given status values (see
158	cancel).	221	cancel).
159		222
160	killall	223	killall
161	Kills/terminates/cancels all coroutines except the currently running	224	Kills/terminates/cancels all coroutines except the currently running
162	one. This is useful after a fork, either in the child or the parent,	225	one. This is useful after a fork, either in the child or the parent,
163	as usually only one of them should inherit the running coroutines.	226	as usually only one of them should inherit the running coroutines.
164		227
165	# dynamic methods	228	Note that while this will try to free some of the main programs
		229	resources, you cannot free all of them, so if a coroutine that is
		230	not the main program calls this function, there will be some
		231	one-time resource leak.
166		232
167	COROUTINE METHODS	233	COROUTINE METHODS
168	These are the methods you can call on coroutine objects.	234	These are the methods you can call on coroutine objects (or to create
		235	them).
169		236
170	new Coro \&sub [, @args...]	237	new Coro \&sub [, @args...]
171	Create a new coroutine and return it. When the sub returns the	238	Create a new coroutine and return it. When the sub returns, the
172	coroutine automatically terminates as if "terminate" with the	239	coroutine automatically terminates as if "terminate" with the
173	returned values were called. To make the coroutine run you must	240	returned values were called. To make the coroutine run you must
174	first put it into the ready queue by calling the ready method.	241	first put it into the ready queue by calling the ready method.
175		242
176	See "async" and "Coro::State::new" for additional info about the	243	See "async" and "Coro::State::new" for additional info about the
177	coroutine environment.	244	coroutine environment.
178		245
179	$success = $coroutine->ready	246	$success = $coroutine->ready
180	Put the given coroutine into the ready queue (according to it's	247	Put the given coroutine into the end of its ready queue (there is
181	priority) and return true. If the coroutine is already in the ready	248	one queue for each priority) and return true. If the coroutine is
182	queue, do nothing and return false.	249	already in the ready queue, do nothing and return false.
		250
		251	This ensures that the scheduler will resume this coroutine
		252	automatically once all the coroutines of higher priority and all
		253	coroutines of the same priority that were put into the ready queue
		254	earlier have been resumed.
183		255
184	$is_ready = $coroutine->is_ready	256	$is_ready = $coroutine->is_ready
185	Return wether the coroutine is currently the ready queue or not,	257	Return whether the coroutine is currently the ready queue or not,
186		258
187	$coroutine->cancel (arg...)	259	$coroutine->cancel (arg...)
188	Terminates the given coroutine and makes it return the given	260	Terminates the given coroutine and makes it return the given
189	arguments as status (default: the empty list). Never returns if the	261	arguments as status (default: the empty list). Never returns if the
190	coroutine is the current coroutine.	262	coroutine is the current coroutine.
191		263
192	$coroutine->join	264	$coroutine->join
193	Wait until the coroutine terminates and return any values given to	265	Wait until the coroutine terminates and return any values given to
194	the "terminate" or "cancel" functions. "join" can be called	266	the "terminate" or "cancel" functions. "join" can be called
195	concurrently from multiple coroutines.	267	concurrently from multiple coroutines, and all will be resumed and
		268	given the status return once the $coroutine terminates.
196		269
197	$coroutine->on_destroy (\&cb)	270	$coroutine->on_destroy (\&cb)
198	Registers a callback that is called when this coroutine gets	271	Registers a callback that is called when this coroutine gets
199	destroyed, but before it is joined. The callback gets passed the	272	destroyed, but before it is joined. The callback gets passed the
200	terminate arguments, if any.	273	terminate arguments, if any, and must not die, under any
		274	circumstances.
201		275
202	$oldprio = $coroutine->prio ($newprio)	276	$oldprio = $coroutine->prio ($newprio)
203	Sets (or gets, if the argument is missing) the priority of the	277	Sets (or gets, if the argument is missing) the priority of the
204	coroutine. Higher priority coroutines get run before lower priority	278	coroutine. Higher priority coroutines get run before lower priority
205	coroutines. Priorities are small signed integers (currently -4 ..	279	coroutines. Priorities are small signed integers (currently -4 ..
…		…
249	well end the whole program.	323	well end the whole program.
250		324
251	GLOBAL FUNCTIONS	325	GLOBAL FUNCTIONS
252	Coro::nready	326	Coro::nready
253	Returns the number of coroutines that are currently in the ready	327	Returns the number of coroutines that are currently in the ready
254	state, i.e. that can be switched to. The value 0 means that the only	328	state, i.e. that can be switched to by calling "schedule" directory
255	runnable coroutine is the currently running one, so "cede" would	329	or indirectly. The value 0 means that the only runnable coroutine is
256	have no effect, and "schedule" would cause a deadlock unless there	330	the currently running one, so "cede" would have no effect, and
		331	"schedule" would cause a deadlock unless there is an idle handler
257	is an idle handler that wakes up some coroutines.	332	that wakes up some coroutines.
258		333
259	my $guard = Coro::guard { ... }	334	my $guard = Coro::guard { ... }
260	This creates and returns a guard object. Nothing happens until the	335	This creates and returns a guard object. Nothing happens until the
261	object gets destroyed, in which case the codeblock given as argument	336	object gets destroyed, in which case the codeblock given as argument
262	will be executed. This is useful to free locks or other resources in	337	will be executed. This is useful to free locks or other resources in
…		…
275	# do something that requires $busy to be true	350	# do something that requires $busy to be true
276	}	351	}
277		352
278	unblock_sub { ... }	353	unblock_sub { ... }
279	This utility function takes a BLOCK or code reference and "unblocks"	354	This utility function takes a BLOCK or code reference and "unblocks"
280	it, returning the new coderef. This means that the new coderef will	355	it, returning a new coderef. Unblocking means that calling the new
281	return immediately without blocking, returning nothing, while the	356	coderef will return immediately without blocking, returning nothing,
282	original code ref will be called (with parameters) from within its	357	while the original code ref will be called (with parameters) from
283	own coroutine.	358	within another coroutine.
284		359
285	The reason this function exists is that many event libraries (such	360	The reason this function exists is that many event libraries (such
286	as the venerable Event module) are not coroutine-safe (a weaker form	361	as the venerable Event module) are not coroutine-safe (a weaker form
287	of thread-safety). This means you must not block within event	362	of thread-safety). This means you must not block within event
288	callbacks, otherwise you might suffer from crashes or worse.	363	callbacks, otherwise you might suffer from crashes or worse. The
		364	only event library currently known that is safe to use without
		365	"unblock_sub" is EV.
289		366
290	This function allows your callbacks to block by executing them in	367	This function allows your callbacks to block by executing them in
291	another coroutine where it is safe to block. One example where	368	another coroutine where it is safe to block. One example where
292	blocking is handy is when you use the Coro::AIO functions to save	369	blocking is handy is when you use the Coro::AIO functions to save
293	results to disk.	370	results to disk, for example.
294		371
295	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	372	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
296	when creating event callbacks that want to block.	373	when creating event callbacks that want to block.
297		374
		375	If your handler does not plan to block (e.g. simply sends a message
		376	to another coroutine, or puts some other coroutine into the ready
		377	queue), there is no reason to use "unblock_sub".
		378
		379	Note that you also need to use "unblock_sub" for any other callbacks
		380	that are indirectly executed by any C-based event loop. For example,
		381	when you use a module that uses AnyEvent (and you use
		382	Coro::AnyEvent) and it provides callbacks that are the result of
		383	some event callback, then you must not block either, or use
		384	"unblock_sub".
		385
298	BUGS/LIMITATIONS	386	BUGS/LIMITATIONS
299	- you must make very sure that no coro is still active on global
300	destruction. very bad things might happen otherwise (usually segfaults).
301
302	- this module is not thread-safe. You should only ever use this module	387	This module is not perl-pseudo-thread-safe. You should only ever use
303	from the same thread (this requirement might be loosened in the future	388	this module from the same thread (this requirement might be removed in
304	to allow per-thread schedulers, but Coro::State does not yet allow	389	the future to allow per-thread schedulers, but Coro::State does not yet
305	this).	390	allow this). I recommend disabling thread support and using processes,
		391	as this is much faster and uses less memory.
306		392
307	SEE ALSO	393	SEE ALSO
308	Lower level Configuration, Coroutine Environment: Coro::State.	394	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
309		395
310	Debugging: Coro::Debug.	396	Debugging: Coro::Debug.
311		397
312	Support/Utility: Coro::Specific, Coro::Util.	398	Support/Utility: Coro::Specific, Coro::Util.
313		399
314	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	400	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
315	Coro::SemaphoreSet, Coro::RWLock.	401	Coro::SemaphoreSet, Coro::RWLock.
316		402
317	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket.	403	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
318		404
319	Compatibility: Coro::LWP, Coro::Storable, Coro::Select.	405	Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
320		406
321	Embedding: <Coro:MakeMaker>.	407	XS API: Coro::MakeMaker.
		408
		409	Low level Configuration, Coroutine Environment: Coro::State.
322		410
323	AUTHOR	411	AUTHOR
324	Marc Lehmann <schmorp@schmorp.de>	412	Marc Lehmann <schmorp@schmorp.de>
325	http://home.schmorp.de/	413	http://home.schmorp.de/
326		414

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Comparing Coro/README (file contents): Revision 1.12 by root, Thu Oct 11 00:38:37 2007 UTC vs. Revision 1.15 by root, Sun Sep 21 01:23:26 2008 UTC

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Comparing Coro/README (file contents):
Revision 1.12 by root, Thu Oct 11 00:38:37 2007 UTC vs.
Revision 1.15 by root, Sun Sep 21 01:23:26 2008 UTC