[ViewVC] Diff of: cvs/Coro/README

Comparing Coro/README (file contents):
Revision 1.13 by root, Mon Dec 17 06:47:33 2007 UTC vs.
Revision 1.14 by root, Sat May 10 22:32:40 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	my $lock = new Coro::Semaphore;	19	my $lock = new Coro::Semaphore;
20	my $locked;	20	my $locked;
21		21
22	$lock->down;	22	$lock->down;
23	$locked = 1;	23	$locked = 1;
24	$lock->up;	24	$lock->up;
25		25
26	DESCRIPTION	26	DESCRIPTION
27	This module collection manages coroutines. Coroutines are similar to	27	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.	28	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	29	SMP machines. The specific flavor of coroutine used in this module also
30	that it will not switch between coroutines unless necessary, at	30	guarantees you that it will not switch between coroutines unless
31	easily-identified points in your program, so locking and parallel access	31	necessary, at easily-identified points in your program, so locking and
32	are rarely an issue, making coroutine programming much safer than	32	parallel access are rarely an issue, making coroutine programming much
33	threads programming.	33	safer and easier than threads programming.
34		34
35	(Perl, however, does not natively support real threads but instead does	35	Unlike a normal perl program, however, coroutines allow you to have
36	a very slow and memory-intensive emulation of processes using threads.	36	multiple running interpreters that share data, which is especially
37	This is a performance win on Windows machines, and a loss everywhere	37	useful to code pseudo-parallel processes and for event-based
38	else).	38	programming, such as multiple HTTP-GET requests running concurrently.
		39	See Coro::AnyEvent to learn more.
		40
		41	Coroutines are also useful because Perl has no support for threads (the
		42	so called "threads" that perl offers are nothing more than the (bad)
		43	process emulation coming from the Windows platform: On standard
		44	operating systems they serve no purpose whatsoever, except by making
		45	your programs slow and making them use a lot of memory. Best disable
		46	them when building perl, or aks your software vendor/distributor to do
		47	it for you).
39		48
40	In this module, coroutines are defined as "callchain + lexical variables	49	In this module, coroutines are defined as "callchain + lexical variables
41	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	50	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
42	callchain, its own set of lexicals and its own set of perls most	51	callchain, its own set of lexicals and its own set of perls most
43	important global variables (see Coro::State for more configuration).	52	important global variables (see Coro::State for more configuration).
44		53
45	$main	54	$Coro::main
46	This coroutine represents the main program.	55	This variable stores the coroutine object that represents the main
		56	program. While you cna "ready" it and do most other things you can
		57	do to coroutines, it is mainly useful to compare again
		58	$Coro::current, to see wether you are running in the main program or
		59	not.
47		60
48	$current (or as function: current)	61	$Coro::current
49	The current coroutine (the last coroutine switched to). The initial	62	The coroutine object representing the current coroutine (the last
		63	coroutine that the Coro scheduler switched to). The initial value is
50	value is $main (of course).	64	$main (of course).
51		65
52	This variable is strictly read-only. It is provided for	66	This variable is strictly read-only. You can take copies of the
53	performance reasons. If performance is not essential you are	67	value stored in it and use it as any other coroutine object, but you
54	encouraged to use the "Coro::current" function instead.	68	must not otherwise modify the variable itself.
55		69
56	$idle	70	$Coro::idle
57	A callback that is called whenever the scheduler finds no ready	71	This variable is mainly useful to integrate Coro into event loops.
58	coroutines to run. The default implementation prints "FATAL:	72	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	73	this is pretty low-level functionality.
60	to continue.	74
		75	This variable stores a callback that is called whenever the
		76	scheduler finds no ready coroutines to run. The default
		77	implementation prints "FATAL: deadlock detected" and exits, because
		78	the program has no other way to continue.
61		79
62	This hook is overwritten by modules such as "Coro::Timer" and	80	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	81	"Coro::AnyEvent" to wait on an external event that hopefully wake up
64	coroutine so the scheduler can run it.	82	a coroutine so the scheduler can run it.
		83
		84	Note that the callback must not, under any circumstances, block
		85	the current coroutine. Normally, this is achieved by having an "idle
		86	coroutine" that calls the event loop and then blocks again, and then
		87	readying that coroutine in the idle handler.
		88
		89	See Coro::Event or Coro::AnyEvent for examples of using this
		90	technique.
65		91
66	Please note that if your callback recursively invokes perl (e.g. for	92	Please note that if your callback recursively invokes perl (e.g. for
67	event handlers), then it must be prepared to be called recursively	93	event handlers), then it must be prepared to be called recursively
68	itself.	94	itself.
69		95
70	STATIC METHODS	96	SIMPLE COROUTINE CREATION
71	Static methods are actually functions that operate on the current
72	coroutine only.
73
74	async { ... } [@args...]	97	async { ... } [@args...]
75	Create a new asynchronous coroutine and return it's coroutine object	98	Create a new coroutine and return it's coroutine object (usually
76	(usually unused). When the sub returns the new coroutine is	99	unused). The coroutine will be put into the ready queue, so it will
		100	start running automatically on the next scheduler run.
		101
		102	The first argument is a codeblock/closure that should be executed in
		103	the coroutine. When it returns argument returns the coroutine is
77	automatically terminated.	104	automatically terminated.
78		105
		106	The remaining arguments are passed as arguments to the closure.
		107
79	See the "Coro::State::new" constructor for info about the coroutine	108	See the "Coro::State::new" constructor for info about the coroutine
80	environment in which coroutines run.	109	environment in which coroutines are executed.
81		110
82	Calling "exit" in a coroutine will do the same as calling exit	111	Calling "exit" in a coroutine will do the same as calling exit
83	outside the coroutine. Likewise, when the coroutine dies, the	112	outside the coroutine. Likewise, when the coroutine dies, the
84	program will exit, just as it would in the main program.	113	program will exit, just as it would in the main program.
85		114
		115	If you do not want that, you can provide a default "die" handler, or
		116	simply avoid dieing (by use of "eval").
		117
86	# create a new coroutine that just prints its arguments	118	Example: Create a new coroutine that just prints its arguments.
		119
87	async {	120	async {
88	print "@_\n";	121	print "@_\n";
89	} 1,2,3,4;	122	} 1,2,3,4;
90		123
91	async_pool { ... } [@args...]	124	async_pool { ... } [@args...]
92	Similar to "async", but uses a coroutine pool, so you should not	125	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	126	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	127	get a coroutine that might have executed other code already (which
95	good or bad :).	128	can be good or bad :).
96		129
		130	On the plus side, this function is faster than creating (and
		131	destroying) a completely new coroutine, so if you need a lot of
		132	generic coroutines in quick successsion, use "async_pool", not
		133	"async".
		134
97	Also, the block is executed in an "eval" context and a warning will	135	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	136	be issued in case of an exception instead of terminating the
99	program, as "async" does. As the coroutine is being reused, stuff	137	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	138	like "on_destroy" will not work in the expected way, unless you call
101	terminate or cancel, which somehow defeats the purpose of pooling.	139	terminate or cancel, which somehow defeats the purpose of pooling
		140	(but is fine in the exceptional case).
102		141
103	The priority will be reset to 0 after each job, tracing will be	142	The priority will be reset to 0 after each run, tracing will be
104	disabled, the description will be reset and the default output	143	disabled, the description will be reset and the default output
105	filehandle gets restored, so you can change alkl these. Otherwise	144	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	145	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	146	per-coroutine global stuff such as $/ you must needs to revert
108	change, which is most simply done by using local as in " local $/ ".	147	that change, which is most simply done by using local as in: " local
		148	$/ ".
109		149
110	The pool size is limited to 8 idle coroutines (this can be adjusted	150	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	151	by changing $Coro::POOL_SIZE), and there can be as many non-idle
112	coros as required.	152	coros as required.
113		153
114	If you are concerned about pooled coroutines growing a lot because a	154	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.	155	single "async_pool" used a lot of stackspace you can e.g.
116	"async_pool { terminate }" once per second or so to slowly replenish	156	"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	157	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	158	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also
119	also exit.	159	be destroyed.
		160
		161	STATIC METHODS
		162	Static methods are actually functions that operate on the current
		163	coroutine.
120		164
121	schedule	165	schedule
122	Calls the scheduler. Please note that the current coroutine 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
123	be put into the ready queue, so calling this function usually means	173	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	174	be called again unless something else (e.g. an event handler) calls
125	handler) calls ready.	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 wether the
		183	event indeed happened, e.g. by storing the status in a variable.
126		184
127	The canonical way to wait on external events is this:	185	The canonical way to wait on external events is this:
128		186
129	{	187	{
130	# remember current coroutine	188	# remember current coroutine
145		203
146	cede	204	cede
147	"Cede" to other coroutines. This function puts the current coroutine	205	"Cede" to other coroutines. This function puts the current coroutine
148	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
149	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
150	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.
151		212
152	Coro::cede_notself	213	Coro::cede_notself
153	Works like cede, but is not exported by default and will cede to any	214	Works like cede, but is not exported by default and will cede to
154	coroutine, regardless of priority, once.	215	any coroutine, regardless of priority. This is useful sometimes to
		216	ensure progress is made.
155		217
156	terminate [arg...]	218	terminate [arg...]
157	Terminates the current coroutine with the given status values (see	219	Terminates the current coroutine with the given status values (see
158	cancel).	220	cancel).
159		221
160	killall	222	killall
161	Kills/terminates/cancels all coroutines except the currently running	223	Kills/terminates/cancels all coroutines except the currently running
162	one. This is useful after a fork, either in the child or the parent,	224	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.	225	as usually only one of them should inherit the running coroutines.
164		226
165	# dynamic methods	227	Note that while this will try to free some of the main programs
		228	resources, you cnanot 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.
166		231
167	COROUTINE METHODS	232	COROUTINE METHODS
168	These are the methods you can call on coroutine objects.	233	These are the methods you can call on coroutine objects (or to create
		234	them).
169		235
170	new Coro \&sub [, @args...]	236	new Coro \&sub [, @args...]
171	Create a new coroutine and return it. When the sub returns the	237	Create a new coroutine and return it. When the sub returns, the
172	coroutine automatically terminates as if "terminate" with the	238	coroutine automatically terminates as if "terminate" with the
173	returned values were called. To make the coroutine run you must	239	returned values were called. To make the coroutine run you must
174	first put it into the ready queue by calling the ready method.	240	first put it into the ready queue by calling the ready method.
175		241
176	See "async" and "Coro::State::new" for additional info about the	242	See "async" and "Coro::State::new" for additional info about the
177	coroutine environment.	243	coroutine environment.
178		244
179	$success = $coroutine->ready	245	$success = $coroutine->ready
180	Put the given coroutine into the ready queue (according to it's	246	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	247	one queue for each priority) and return true. If the coroutine is
182	queue, do nothing and return false.	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.
183		254
184	$is_ready = $coroutine->is_ready	255	$is_ready = $coroutine->is_ready
185	Return wether the coroutine is currently the ready queue or not,	256	Return wether the coroutine is currently the ready queue or not,
186		257
187	$coroutine->cancel (arg...)	258	$coroutine->cancel (arg...)
…		…
190	coroutine is the current coroutine.	261	coroutine is the current coroutine.
191		262
192	$coroutine->join	263	$coroutine->join
193	Wait until the coroutine terminates and return any values given to	264	Wait until the coroutine terminates and return any values given to
194	the "terminate" or "cancel" functions. "join" can be called	265	the "terminate" or "cancel" functions. "join" can be called
195	concurrently from multiple coroutines.	266	concurrently from multiple coroutines, and all will be resumed and
		267	given the status return once the $coroutine terminates.
196		268
197	$coroutine->on_destroy (\&cb)	269	$coroutine->on_destroy (\&cb)
198	Registers a callback that is called when this coroutine gets	270	Registers a callback that is called when this coroutine gets
199	destroyed, but before it is joined. The callback gets passed the	271	destroyed, but before it is joined. The callback gets passed the
200	terminate arguments, if any.	272	terminate arguments, if any, and must not die, under any
		273	circumstances.
201		274
202	$oldprio = $coroutine->prio ($newprio)	275	$oldprio = $coroutine->prio ($newprio)
203	Sets (or gets, if the argument is missing) the priority of the	276	Sets (or gets, if the argument is missing) the priority of the
204	coroutine. Higher priority coroutines get run before lower priority	277	coroutine. Higher priority coroutines get run before lower priority
205	coroutines. Priorities are small signed integers (currently -4 ..	278	coroutines. Priorities are small signed integers (currently -4 ..
…		…
249	well end the whole program.	322	well end the whole program.
250		323
251	GLOBAL FUNCTIONS	324	GLOBAL FUNCTIONS
252	Coro::nready	325	Coro::nready
253	Returns the number of coroutines that are currently in the ready	326	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	327	state, i.e. that can be switched to by calling "schedule" directory
255	runnable coroutine is the currently running one, so "cede" would	328	or indirectly. The value 0 means that the only runnable coroutine is
256	have no effect, and "schedule" would cause a deadlock unless there	329	the currently running one, so "cede" would have no effect, and
		330	"schedule" would cause a deadlock unless there is an idle handler
257	is an idle handler that wakes up some coroutines.	331	that wakes up some coroutines.
258		332
259	my $guard = Coro::guard { ... }	333	my $guard = Coro::guard { ... }
260	This creates and returns a guard object. Nothing happens until the	334	This creates and returns a guard object. Nothing happens until the
261	object gets destroyed, in which case the codeblock given as argument	335	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	336	will be executed. This is useful to free locks or other resources in
…		…
275	# do something that requires $busy to be true	349	# do something that requires $busy to be true
276	}	350	}
277		351
278	unblock_sub { ... }	352	unblock_sub { ... }
279	This utility function takes a BLOCK or code reference and "unblocks"	353	This utility function takes a BLOCK or code reference and "unblocks"
280	it, returning the new coderef. This means that the new coderef will	354	it, returning a new coderef. Unblocking means that calling the new
281	return immediately without blocking, returning nothing, while the	355	coderef will return immediately without blocking, returning nothing,
282	original code ref will be called (with parameters) from within its	356	while the original code ref will be called (with parameters) from
283	own coroutine.	357	within another coroutine.
284		358
285	The reason this function exists is that many event libraries (such	359	The reason this function exists is that many event libraries (such
286	as the venerable Event module) are not coroutine-safe (a weaker form	360	as the venerable Event module) are not coroutine-safe (a weaker form
287	of thread-safety). This means you must not block within event	361	of thread-safety). This means you must not block within event
288	callbacks, otherwise you might suffer from crashes or worse.	362	callbacks, otherwise you might suffer from crashes or worse. The
		363	only event library currently known that is safe to use without
		364	"unblock_sub" is EV.
289		365
290	This function allows your callbacks to block by executing them in	366	This function allows your callbacks to block by executing them in
291	another coroutine where it is safe to block. One example where	367	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	368	blocking is handy is when you use the Coro::AIO functions to save
293	results to disk.	369	results to disk, for example.
294		370
295	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	371	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
296	when creating event callbacks that want to block.	372	when creating event callbacks that want to block.
297		373
		374	If your handler does not plan to block (e.g. simply sends a message
		375	to another coroutine, or puts some other coroutine into the ready
		376	queue), there is no reason to use "unblock_sub".
		377
		378	Note that you also need to use "unblock_sub" for any other callbacks
		379	that are indirectly executed by any C-based event loop. For example,
		380	when you use a module that uses AnyEvent (and you use
		381	Coro::AnyEvent) and it provides callbacks that are the result of
		382	some event callback, then you must not block either, or use
		383	"unblock_sub".
		384
298	BUGS/LIMITATIONS	385	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	386	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	387	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	388	the future to allow per-thread schedulers, but Coro::State does not yet
305	this).	389	allow this). I recommend disabling thread support and using processes,
		390	as this is much faster and uses less memory.
306		391
307	SEE ALSO	392	SEE ALSO
308	Lower level Configuration, Coroutine Environment: Coro::State.	393	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
309		394
310	Debugging: Coro::Debug.	395	Debugging: Coro::Debug.
311		396
312	Support/Utility: Coro::Specific, Coro::Util.	397	Support/Utility: Coro::Specific, Coro::Util.
313		398
314	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	399	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
315	Coro::SemaphoreSet, Coro::RWLock.	400	Coro::SemaphoreSet, Coro::RWLock.
316		401
317	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket.	402	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
318		403
319	Compatibility: Coro::LWP, Coro::Storable, Coro::Select.	404	Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
320		405
321	Embedding: Coro::MakeMaker.	406	XS API: Coro::MakeMaker.
		407
		408	Low level Configuration, Coroutine Environment: Coro::State.
322		409
323	AUTHOR	410	AUTHOR
324	Marc Lehmann <schmorp@schmorp.de>	411	Marc Lehmann <schmorp@schmorp.de>
325	http://home.schmorp.de/	412	http://home.schmorp.de/
326		413

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Comparing Coro/README (file contents): Revision 1.13 by root, Mon Dec 17 06:47:33 2007 UTC vs. Revision 1.14 by root, Sat May 10 22:32:40 2008 UTC

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Comparing Coro/README (file contents):
Revision 1.13 by root, Mon Dec 17 06:47:33 2007 UTC vs.
Revision 1.14 by root, Sat May 10 22:32:40 2008 UTC