[ViewVC] Diff of: cvs/Coro/README

Comparing Coro/README (file contents):
Revision 1.9 by root, Sat Sep 29 19:42:08 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";
		10	cede; # yield back to main
		11	print "4\n";
9	};	12	};
10		13	print "1\n";
11	# alternatively create an async coroutine 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 at the same time even on SMP machines.	29	threads but don't (in general) run in parallel at the same time even on
22	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
23	that it will not switch between coroutines unless necessary, at	31	guarantees you that it will not switch between coroutines unless
24	easily-identified points in your program, so locking and parallel access	32	necessary, at easily-identified points in your program, so locking and
25	are rarely an issue, making coroutine programming much safer than	33	parallel access are rarely an issue, making coroutine programming much
26	threads programming.	34	safer and easier than threads programming.
27		35
28	(Perl, however, does not natively support real threads but instead does	36	Unlike a normal perl program, however, coroutines allow you to have
29	a very slow and memory-intensive emulation of processes using threads.	37	multiple running interpreters that share data, which is especially
30	This is a performance win on Windows machines, and a loss everywhere	38	useful to code pseudo-parallel processes and for event-based
31	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).
32		49
33	In this module, coroutines are defined as "callchain + lexical variables	50	In this module, coroutines are defined as "callchain + lexical variables
34	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own	51	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
35	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
36	important global variables.	53	important global variables (see Coro::State for more configuration).
37		54
38	$main	55	$Coro::main
39	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.
40		61
41	$current (or as function: current)	62	$Coro::current
42	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
43	value is $main (of course).	65	$main (of course).
44		66
45	This variable is strictly read-only. It is provided for	67	This variable is strictly read-only. You can take copies of the
46	performance reasons. If performance is not essential you are	68	value stored in it and use it as any other coroutine object, but you
47	encouraged to use the "Coro::current" function instead.	69	must not otherwise modify the variable itself.
48		70
49	$idle	71	$Coro::idle
50	A callback that is called whenever the scheduler finds no ready	72	This variable is mainly useful to integrate Coro into event loops.
51	coroutines to run. The default implementation prints "FATAL:	73	It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as
52	deadlock detected" and exits, because the program has no other way	74	this is pretty low-level functionality.
53	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.
54		80
55	This hook is overwritten by modules such as "Coro::Timer" and	81	This hook is overwritten by modules such as "Coro::Timer" and
56	"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
57	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.
58		92
59	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
60	event handlers), then it must be prepared to be called recursively.	94	event handlers), then it must be prepared to be called recursively
		95	itself.
61		96
62	STATIC METHODS	97	SIMPLE COROUTINE CREATION
63	Static methods are actually functions that operate on the current
64	coroutine only.
65
66	async { ... } [@args...]	98	async { ... } [@args...]
67	Create a new asynchronous coroutine and return it's coroutine object	99	Create a new coroutine and return it's coroutine object (usually
68	(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
69	automatically terminated.	105	automatically terminated.
		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.
70		111
71	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
72	outside the coroutine. Likewise, when the coroutine dies, the	113	outside the coroutine. Likewise, when the coroutine dies, the
73	program will exit, just as it would in the main program.	114	program will exit, just as it would in the main program.
74		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
75	# create a new coroutine that just prints its arguments	119	Example: Create a new coroutine that just prints its arguments.
		120
76	async {	121	async {
77	print "@_\n";	122	print "@_\n";
78	} 1,2,3,4;	123	} 1,2,3,4;
79		124
80	async_pool { ... } [@args...]	125	async_pool { ... } [@args...]
81	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
82	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
83	coroutine that might have executed other code already (which can be	128	get a coroutine that might have executed other code already (which
84	good or bad :).	129	can be good or bad :).
85		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
86	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
87	be issued in case of an exception instead of terminating the	137	be issued in case of an exception instead of terminating the
88	program, as "async" does. As the coroutine is being reused, stuff	138	program, as "async" does. As the coroutine is being reused, stuff
89	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
90	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).
91		142
92	The priority will be reset to 0 after each job, otherwise the	143	The priority will be reset to 0 after each run, tracing will be
93	coroutine will be re-used "as-is".	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 to revert
		148	that change, which is most simply done by using local as in: " local
		149	$/ ".
94		150
95	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
96	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
97	coros as required.	153	coros as required.
98		154
99	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
100	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.
101	"async_pool { terminate }" once per second or so to slowly replenish	157	"async_pool { terminate }" once per second or so to slowly replenish
102	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
103	grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will	159	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also
104	also exit.	160	be destroyed.
		161
		162	STATIC METHODS
		163	Static methods are actually functions that operate on the current
		164	coroutine.
105		165
106	schedule	166	schedule
107	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
108	be put into the ready queue, so calling this function usually means	174	ready queue, so calling this function usually means you will never
109	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
110	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.
111		185
112	The canonical way to wait on external events is this:	186	The canonical way to wait on external events is this:
113		187
114	{	188	{
115	# remember current coroutine	189	# remember current coroutine
130		204
131	cede	205	cede
132	"Cede" to other coroutines. This function puts the current coroutine	206	"Cede" to other coroutines. This function puts the current coroutine
133	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
134	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
135	higher priority.	209	higher priority. Once your coroutine gets its turn again it will
		210	automatically be resumed.
136		211
137	Returns true if at least one coroutine switch has happened.	212	This function is often called "yield" in other languages.
138		213
139	Coro::cede_notself	214	Coro::cede_notself
140	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
141	coroutine, regardless of priority, once.	216	any coroutine, regardless of priority. This is useful sometimes to
142		217	ensure progress is made.
143	Returns true if at least one coroutine switch has happened.
144		218
145	terminate [arg...]	219	terminate [arg...]
146	Terminates the current coroutine with the given status values (see	220	Terminates the current coroutine with the given status values (see
147	cancel).	221	cancel).
148		222
149	# dynamic methods	223	killall
		224	Kills/terminates/cancels all coroutines except the currently running
		225	one. This is useful after a fork, either in the child or the parent,
		226	as usually only one of them should inherit the running coroutines.
		227
		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.
150		232
151	COROUTINE METHODS	233	COROUTINE METHODS
152	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).
153		236
154	new Coro \&sub [, @args...]	237	new Coro \&sub [, @args...]
155	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
156	coroutine automatically terminates as if "terminate" with the	239	coroutine automatically terminates as if "terminate" with the
157	returned values were called. To make the coroutine run you must	240	returned values were called. To make the coroutine run you must
158	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.
159		242
160	See "async" for additional discussion.	243	See "async" and "Coro::State::new" for additional info about the
		244	coroutine environment.
161		245
162	$success = $coroutine->ready	246	$success = $coroutine->ready
163	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
164	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
165	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.
166		255
167	$is_ready = $coroutine->is_ready	256	$is_ready = $coroutine->is_ready
168	Return wether the coroutine is currently the ready queue or not,	257	Return whether the coroutine is currently the ready queue or not,
169		258
170	$coroutine->cancel (arg...)	259	$coroutine->cancel (arg...)
171	Terminates the given coroutine and makes it return the given	260	Terminates the given coroutine and makes it return the given
172	arguments as status (default: the empty list). Never returns if the	261	arguments as status (default: the empty list). Never returns if the
173	coroutine is the current coroutine.	262	coroutine is the current coroutine.
174		263
175	$coroutine->join	264	$coroutine->join
176	Wait until the coroutine terminates and return any values given to	265	Wait until the coroutine terminates and return any values given to
177	the "terminate" or "cancel" functions. "join" can be called multiple	266	the "terminate" or "cancel" functions. "join" can be called
178	times from multiple coroutine.	267	concurrently from multiple coroutines, and all will be resumed and
		268	given the status return once the $coroutine terminates.
179		269
180	$coroutine->on_destroy (\&cb)	270	$coroutine->on_destroy (\&cb)
181	Registers a callback that is called when this coroutine gets	271	Registers a callback that is called when this coroutine gets
182	destroyed, but before it is joined. The callback gets passed the	272	destroyed, but before it is joined. The callback gets passed the
183	terminate arguments, if any.	273	terminate arguments, if any, and must not die, under any
		274	circumstances.
184		275
185	$oldprio = $coroutine->prio ($newprio)	276	$oldprio = $coroutine->prio ($newprio)
186	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
187	coroutine. Higher priority coroutines get run before lower priority	278	coroutine. Higher priority coroutines get run before lower priority
188	coroutines. Priorities are small signed integers (currently -4 ..	279	coroutines. Priorities are small signed integers (currently -4 ..
…		…
211	$olddesc = $coroutine->desc ($newdesc)	302	$olddesc = $coroutine->desc ($newdesc)
212	Sets (or gets in case the argument is missing) the description for	303	Sets (or gets in case the argument is missing) the description for
213	this coroutine. This is just a free-form string you can associate	304	this coroutine. This is just a free-form string you can associate
214	with a coroutine.	305	with a coroutine.
215		306
		307	This method simply sets the "$coroutine->{desc}" member to the given
		308	string. You can modify this member directly if you wish.
		309
		310	$coroutine->throw ([$scalar])
		311	If $throw is specified and defined, it will be thrown as an
		312	exception inside the coroutine at the next convinient point in time
		313	(usually after it gains control at the next schedule/transfer/cede).
		314	Otherwise clears the exception object.
		315
		316	The exception object will be thrown "as is" with the specified
		317	scalar in $@, i.e. if it is a string, no line number or newline will
		318	be appended (unlike with "die").
		319
		320	This can be used as a softer means than "cancel" to ask a coroutine
		321	to end itself, although there is no guarentee that the exception
		322	will lead to termination, and if the exception isn't caught it might
		323	well end the whole program.
		324
216	GLOBAL FUNCTIONS	325	GLOBAL FUNCTIONS
217	Coro::nready	326	Coro::nready
218	Returns the number of coroutines that are currently in the ready	327	Returns the number of coroutines that are currently in the ready
219	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
220	runnable coroutine is the currently running one, so "cede" would	329	or indirectly. The value 0 means that the only runnable coroutine is
221	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
222	is an idle handler that wakes up some coroutines.	332	that wakes up some coroutines.
223		333
224	my $guard = Coro::guard { ... }	334	my $guard = Coro::guard { ... }
225	This creates and returns a guard object. Nothing happens until the	335	This creates and returns a guard object. Nothing happens until the
226	object gets destroyed, in which case the codeblock given as argument	336	object gets destroyed, in which case the codeblock given as argument
227	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
…		…
240	# do something that requires $busy to be true	350	# do something that requires $busy to be true
241	}	351	}
242		352
243	unblock_sub { ... }	353	unblock_sub { ... }
244	This utility function takes a BLOCK or code reference and "unblocks"	354	This utility function takes a BLOCK or code reference and "unblocks"
245	it, returning the new coderef. This means that the new coderef will	355	it, returning a new coderef. Unblocking means that calling the new
246	return immediately without blocking, returning nothing, while the	356	coderef will return immediately without blocking, returning nothing,
247	original code ref will be called (with parameters) from within its	357	while the original code ref will be called (with parameters) from
248	own coroutine.	358	within another coroutine.
249		359
250	The reason this function exists is that many event libraries (such	360	The reason this function exists is that many event libraries (such
251	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
252	of thread-safety). This means you must not block within event	362	of thread-safety). This means you must not block within event
253	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.
254		366
255	This function allows your callbacks to block by executing them in	367	This function allows your callbacks to block by executing them in
256	another coroutine where it is safe to block. One example where	368	another coroutine where it is safe to block. One example where
257	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
258	results to disk.	370	results to disk, for example.
259		371
260	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"	372	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
261	when creating event callbacks that want to block.	373	when creating event callbacks that want to block.
262		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
263	BUGS/LIMITATIONS	386	BUGS/LIMITATIONS
264	- you must make very sure that no coro is still active on global
265	destruction. very bad things might happen otherwise (usually segfaults).
266
267	- 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
268	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
269	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
270	this).	390	allow this). I recommend disabling thread support and using processes,
		391	as this is much faster and uses less memory.
271		392
272	SEE ALSO	393	SEE ALSO
		394	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
		395
		396	Debugging: Coro::Debug.
		397
273	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.	398	Support/Utility: Coro::Specific, Coro::Util.
274		399
275	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,	400	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
276	Coro::SemaphoreSet, Coro::RWLock.	401	Coro::SemaphoreSet, Coro::RWLock.
277		402
278	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,	403	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
279	Coro::Select.
280		404
281	Embedding: <Coro:MakeMaker>	405	Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
		406
		407	XS API: Coro::MakeMaker.
		408
		409	Low level Configuration, Coroutine Environment: Coro::State.
282		410
283	AUTHOR	411	AUTHOR
284	Marc Lehmann <schmorp@schmorp.de>	412	Marc Lehmann <schmorp@schmorp.de>
285	http://home.schmorp.de/	413	http://home.schmorp.de/
286		414

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Comparing Coro/README (file contents): Revision 1.9 by root, Sat Sep 29 19:42:08 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 1.9 by root, Sat Sep 29 19:42:08 2007 UTC vs.
Revision 1.15 by root, Sun Sep 21 01:23:26 2008 UTC