[ViewVC] Contents of: cvs/Coro/README

NAME
    Coro - coroutine process abstraction

SYNOPSIS
     use Coro;

     async {
        # some asynchronous thread of execution
     };

     # alternatively create an async coroutine like this:

     sub some_func : Coro {
        # some more async code
     }

     cede;

DESCRIPTION
    This module collection manages coroutines. Coroutines are similar to
    threads but don't run in parallel at the same time even on SMP machines.
    The specific flavor of coroutine used in this module also guarantees you
    that it will not switch between coroutines unless necessary, at
    easily-identified points in your program, so locking and parallel access
    are rarely an issue, making coroutine programming much safer than
    threads programming.

    (Perl, however, does not natively support real threads but instead does
    a very slow and memory-intensive emulation of processes using threads.
    This is a performance win on Windows machines, and a loss everywhere
    else).

    In this module, coroutines are defined as "callchain + lexical variables
    + @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
    callchain, its own set of lexicals and its own set of perls most
    important global variables.

    $main
        This coroutine represents the main program.

    $current (or as function: current)
        The current coroutine (the last coroutine switched to). The initial
        value is $main (of course).

        This variable is strictly *read-only*. It is provided for
        performance reasons. If performance is not essential you are
        encouraged to use the "Coro::current" function instead.

    $idle
        A callback that is called whenever the scheduler finds no ready
        coroutines to run. The default implementation prints "FATAL:
        deadlock detected" and exits, because the program has no other way
        to continue.

        This hook is overwritten by modules such as "Coro::Timer" and
        "Coro::Event" to wait on an external event that hopefully wake up a
        coroutine so the scheduler can run it.

        Please note that if your callback recursively invokes perl (e.g. for
        event handlers), then it must be prepared to be called recursively.

  STATIC METHODS
    Static methods are actually functions that operate on the current
    coroutine only.

    async { ... } [@args...]
        Create a new asynchronous coroutine and return it's coroutine object
        (usually unused). When the sub returns the new coroutine is
        automatically terminated.

        See the "Coro::State::new" constructor for info about the coroutine
        environment.

        Calling "exit" in a coroutine will do the same as calling exit
        outside the coroutine. Likewise, when the coroutine dies, the
        program will exit, just as it would in the main program.

           # create a new coroutine that just prints its arguments
           async {
              print "@_\n";
           } 1,2,3,4;

    async_pool { ... } [@args...]
        Similar to "async", but uses a coroutine pool, so you should not
        call terminate or join (although you are allowed to), and you get a
        coroutine that might have executed other code already (which can be
        good or bad :).

        Also, the block is executed in an "eval" context and a warning will
        be issued in case of an exception instead of terminating the
        program, as "async" does. As the coroutine is being reused, stuff
        like "on_destroy" will not work in the expected way, unless you call
        terminate or cancel, which somehow defeats the purpose of pooling.

        The priority will be reset to 0 after each job, tracing will be
        disabled, the description will be reset and the default output
        filehandle gets restored, so you can change alkl these. Otherwise
        the coroutine will be re-used "as-is": most notably if you change
        other per-coroutine global stuff such as $/ you need to revert that
        change, which is most simply done by using local as in " local $/ ".

        The pool size is limited to 8 idle coroutines (this can be adjusted
        by changing $Coro::POOL_SIZE), and there can be as many non-idle
        coros as required.

        If you are concerned about pooled coroutines growing a lot because a
        single "async_pool" used a lot of stackspace you can e.g.
        "async_pool { terminate }" once per second or so to slowly replenish
        the pool. In addition to that, when the stacks used by a handler
        grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will
        also exit.

    schedule
        Calls the scheduler. Please note that the current coroutine will not
        be put into the ready queue, so calling this function usually means
        you will never be called again unless something else (e.g. an event
        handler) calls ready.

        The canonical way to wait on external events is this:

           {
              # remember current coroutine
              my $current = $Coro::current;

              # register a hypothetical event handler
              on_event_invoke sub {
                 # wake up sleeping coroutine
                 $current->ready;
                 undef $current;
              };

              # call schedule until event occurred.
              # in case we are woken up for other reasons
              # (current still defined), loop.
              Coro::schedule while $current;
           }

    cede
        "Cede" to other coroutines. This function puts the current coroutine
        into the ready queue and calls "schedule", which has the effect of
        giving up the current "timeslice" to other coroutines of the same or
        higher priority.

        Returns true if at least one coroutine switch has happened.

    Coro::cede_notself
        Works like cede, but is not exported by default and will cede to any
        coroutine, regardless of priority, once.

        Returns true if at least one coroutine switch has happened.

    terminate [arg...]
        Terminates the current coroutine with the given status values (see
        cancel).

    killall
        Kills/terminates/cancels all coroutines except the currently running
        one. This is useful after a fork, either in the child or the parent,
        as usually only one of them should inherit the running coroutines.

    # dynamic methods

  COROUTINE METHODS
    These are the methods you can call on coroutine objects.

    new Coro \&sub [, @args...]
        Create a new coroutine and return it. When the sub returns the
        coroutine automatically terminates as if "terminate" with the
        returned values were called. To make the coroutine run you must
        first put it into the ready queue by calling the ready method.

        See "async" and "Coro::State::new" for additional info about the
        coroutine environment.

    $success = $coroutine->ready
        Put the given coroutine into the ready queue (according to it's
        priority) and return true. If the coroutine is already in the ready
        queue, do nothing and return false.

    $is_ready = $coroutine->is_ready
        Return wether the coroutine is currently the ready queue or not,

    $coroutine->cancel (arg...)
        Terminates the given coroutine and makes it return the given
        arguments as status (default: the empty list). Never returns if the
        coroutine is the current coroutine.

    $coroutine->join
        Wait until the coroutine terminates and return any values given to
        the "terminate" or "cancel" functions. "join" can be called
        concurrently from multiple coroutines.

    $coroutine->on_destroy (\&cb)
        Registers a callback that is called when this coroutine gets
        destroyed, but before it is joined. The callback gets passed the
        terminate arguments, if any.

    $oldprio = $coroutine->prio ($newprio)
        Sets (or gets, if the argument is missing) the priority of the
        coroutine. Higher priority coroutines get run before lower priority
        coroutines. Priorities are small signed integers (currently -4 ..
        +3), that you can refer to using PRIO_xxx constants (use the import
        tag :prio to get then):

           PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
               3    >     1     >      0      >    -1    >    -3     >    -4

           # set priority to HIGH
           current->prio(PRIO_HIGH);

        The idle coroutine ($Coro::idle) always has a lower priority than
        any existing coroutine.

        Changing the priority of the current coroutine will take effect
        immediately, but changing the priority of coroutines in the ready
        queue (but not running) will only take effect after the next
        schedule (of that coroutine). This is a bug that will be fixed in
        some future version.

    $newprio = $coroutine->nice ($change)
        Similar to "prio", but subtract the given value from the priority
        (i.e. higher values mean lower priority, just as in unix).

    $olddesc = $coroutine->desc ($newdesc)
        Sets (or gets in case the argument is missing) the description for
        this coroutine. This is just a free-form string you can associate
        with a coroutine.

        This method simply sets the "$coroutine->{desc}" member to the given
        string. You can modify this member directly if you wish.

    $coroutine->throw ([$scalar])
        If $throw is specified and defined, it will be thrown as an
        exception inside the coroutine at the next convinient point in time
        (usually after it gains control at the next schedule/transfer/cede).
        Otherwise clears the exception object.

        The exception object will be thrown "as is" with the specified
        scalar in $@, i.e. if it is a string, no line number or newline will
        be appended (unlike with "die").

        This can be used as a softer means than "cancel" to ask a coroutine
        to end itself, although there is no guarentee that the exception
        will lead to termination, and if the exception isn't caught it might
        well end the whole program.

  GLOBAL FUNCTIONS
    Coro::nready
        Returns the number of coroutines that are currently in the ready
        state, i.e. that can be switched to. The value 0 means that the only
        runnable coroutine is the currently running one, so "cede" would
        have no effect, and "schedule" would cause a deadlock unless there
        is an idle handler that wakes up some coroutines.

    my $guard = Coro::guard { ... }
        This creates and returns a guard object. Nothing happens until the
        object gets destroyed, in which case the codeblock given as argument
        will be executed. This is useful to free locks or other resources in
        case of a runtime error or when the coroutine gets canceled, as in
        both cases the guard block will be executed. The guard object
        supports only one method, "->cancel", which will keep the codeblock
        from being executed.

        Example: set some flag and clear it again when the coroutine gets
        canceled or the function returns:

           sub do_something {
              my $guard = Coro::guard { $busy = 0 };
              $busy = 1;

              # do something that requires $busy to be true
           }

    unblock_sub { ... }
        This utility function takes a BLOCK or code reference and "unblocks"
        it, returning the new coderef. This means that the new coderef will
        return immediately without blocking, returning nothing, while the
        original code ref will be called (with parameters) from within its
        own coroutine.

        The reason this function exists is that many event libraries (such
        as the venerable Event module) are not coroutine-safe (a weaker form
        of thread-safety). This means you must not block within event
        callbacks, otherwise you might suffer from crashes or worse.

        This function allows your callbacks to block by executing them in
        another coroutine where it is safe to block. One example where
        blocking is handy is when you use the Coro::AIO functions to save
        results to disk.

        In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
        when creating event callbacks that want to block.

BUGS/LIMITATIONS
     - you must make very sure that no coro is still active on global
       destruction. very bad things might happen otherwise (usually segfaults).

     - this module is not thread-safe. You should only ever use this module
       from the same thread (this requirement might be loosened in the future
       to allow per-thread schedulers, but Coro::State does not yet allow
       this).

SEE ALSO
    Support/Utility: Coro::Specific, Coro::State, Coro::Util.

    Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
    Coro::SemaphoreSet, Coro::RWLock.

    Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,
    Coro::Select.

    Embedding: <Coro:MakeMaker>

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/

Revision:	1.11
Committed:	Sat Oct 6 19:25:00 2007 UTC (16 years, 7 months ago) by root
Branch:	MAIN
CVS Tags:	rel-4_03
Changes since 1.10:	+15 -0 lines
Log Message:	* empty log message *
#	Content
1	NAME
2	Coro - coroutine process abstraction
3
4	SYNOPSIS
5	use Coro;
6
7	async {
8	# some asynchronous thread of execution
9	};
10
11	# alternatively create an async coroutine like this:
12
13	sub some_func : Coro {
14	# some more async code
15	}
16
17	cede;
18
19	DESCRIPTION
20	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.
22	The specific flavor of coroutine used in this module also guarantees you
23	that it will not switch between coroutines unless necessary, at
24	easily-identified points in your program, so locking and parallel access
25	are rarely an issue, making coroutine programming much safer than
26	threads programming.
27
28	(Perl, however, does not natively support real threads but instead does
29	a very slow and memory-intensive emulation of processes using threads.
30	This is a performance win on Windows machines, and a loss everywhere
31	else).
32
33	In this module, coroutines are defined as "callchain + lexical variables
34	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
35	callchain, its own set of lexicals and its own set of perls most
36	important global variables.
37
38	$main
39	This coroutine represents the main program.
40
41	$current (or as function: current)
42	The current coroutine (the last coroutine switched to). The initial
43	value is $main (of course).
44
45	This variable is strictly read-only. It is provided for
46	performance reasons. If performance is not essential you are
47	encouraged to use the "Coro::current" function instead.
48
49	$idle
50	A callback that is called whenever the scheduler finds no ready
51	coroutines to run. The default implementation prints "FATAL:
52	deadlock detected" and exits, because the program has no other way
53	to continue.
54
55	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
57	coroutine so the scheduler can run it.
58
59	Please note that if your callback recursively invokes perl (e.g. for
60	event handlers), then it must be prepared to be called recursively.
61
62	STATIC METHODS
63	Static methods are actually functions that operate on the current
64	coroutine only.
65
66	async { ... } [@args...]
67	Create a new asynchronous coroutine and return it's coroutine object
68	(usually unused). When the sub returns the new coroutine is
69	automatically terminated.
70
71	See the "Coro::State::new" constructor for info about the coroutine
72	environment.
73
74	Calling "exit" in a coroutine will do the same as calling exit
75	outside the coroutine. Likewise, when the coroutine dies, the
76	program will exit, just as it would in the main program.
77
78	# create a new coroutine that just prints its arguments
79	async {
80	print "@_\n";
81	} 1,2,3,4;
82
83	async_pool { ... } [@args...]
84	Similar to "async", but uses a coroutine pool, so you should not
85	call terminate or join (although you are allowed to), and you get a
86	coroutine that might have executed other code already (which can be
87	good or bad :).
88
89	Also, the block is executed in an "eval" context and a warning will
90	be issued in case of an exception instead of terminating the
91	program, as "async" does. As the coroutine is being reused, stuff
92	like "on_destroy" will not work in the expected way, unless you call
93	terminate or cancel, which somehow defeats the purpose of pooling.
94
95	The priority will be reset to 0 after each job, tracing will be
96	disabled, the description will be reset and the default output
97	filehandle gets restored, so you can change alkl these. Otherwise
98	the coroutine will be re-used "as-is": most notably if you change
99	other per-coroutine global stuff such as $/ you need to revert that
100	change, which is most simply done by using local as in " local $/ ".
101
102	The pool size is limited to 8 idle coroutines (this can be adjusted
103	by changing $Coro::POOL_SIZE), and there can be as many non-idle
104	coros as required.
105
106	If you are concerned about pooled coroutines growing a lot because a
107	single "async_pool" used a lot of stackspace you can e.g.
108	"async_pool { terminate }" once per second or so to slowly replenish
109	the pool. In addition to that, when the stacks used by a handler
110	grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will
111	also exit.
112
113	schedule
114	Calls the scheduler. Please note that the current coroutine will not
115	be put into the ready queue, so calling this function usually means
116	you will never be called again unless something else (e.g. an event
117	handler) calls ready.
118
119	The canonical way to wait on external events is this:
120
121	{
122	# remember current coroutine
123	my $current = $Coro::current;
124
125	# register a hypothetical event handler
126	on_event_invoke sub {
127	# wake up sleeping coroutine
128	$current->ready;
129	undef $current;
130	};
131
132	# call schedule until event occurred.
133	# in case we are woken up for other reasons
134	# (current still defined), loop.
135	Coro::schedule while $current;
136	}
137
138	cede
139	"Cede" to other coroutines. This function puts the current coroutine
140	into the ready queue and calls "schedule", which has the effect of
141	giving up the current "timeslice" to other coroutines of the same or
142	higher priority.
143
144	Returns true if at least one coroutine switch has happened.
145
146	Coro::cede_notself
147	Works like cede, but is not exported by default and will cede to any
148	coroutine, regardless of priority, once.
149
150	Returns true if at least one coroutine switch has happened.
151
152	terminate [arg...]
153	Terminates the current coroutine with the given status values (see
154	cancel).
155
156	killall
157	Kills/terminates/cancels all coroutines except the currently running
158	one. This is useful after a fork, either in the child or the parent,
159	as usually only one of them should inherit the running coroutines.
160
161	# dynamic methods
162
163	COROUTINE METHODS
164	These are the methods you can call on coroutine objects.
165
166	new Coro \&sub [, @args...]
167	Create a new coroutine and return it. When the sub returns the
168	coroutine automatically terminates as if "terminate" with the
169	returned values were called. To make the coroutine run you must
170	first put it into the ready queue by calling the ready method.
171
172	See "async" and "Coro::State::new" for additional info about the
173	coroutine environment.
174
175	$success = $coroutine->ready
176	Put the given coroutine into the ready queue (according to it's
177	priority) and return true. If the coroutine is already in the ready
178	queue, do nothing and return false.
179
180	$is_ready = $coroutine->is_ready
181	Return wether the coroutine is currently the ready queue or not,
182
183	$coroutine->cancel (arg...)
184	Terminates the given coroutine and makes it return the given
185	arguments as status (default: the empty list). Never returns if the
186	coroutine is the current coroutine.
187
188	$coroutine->join
189	Wait until the coroutine terminates and return any values given to
190	the "terminate" or "cancel" functions. "join" can be called
191	concurrently from multiple coroutines.
192
193	$coroutine->on_destroy (\&cb)
194	Registers a callback that is called when this coroutine gets
195	destroyed, but before it is joined. The callback gets passed the
196	terminate arguments, if any.
197
198	$oldprio = $coroutine->prio ($newprio)
199	Sets (or gets, if the argument is missing) the priority of the
200	coroutine. Higher priority coroutines get run before lower priority
201	coroutines. Priorities are small signed integers (currently -4 ..
202	+3), that you can refer to using PRIO_xxx constants (use the import
203	tag :prio to get then):
204
205	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
206	3 > 1 > 0 > -1 > -3 > -4
207
208	# set priority to HIGH
209	current->prio(PRIO_HIGH);
210
211	The idle coroutine ($Coro::idle) always has a lower priority than
212	any existing coroutine.
213
214	Changing the priority of the current coroutine will take effect
215	immediately, but changing the priority of coroutines in the ready
216	queue (but not running) will only take effect after the next
217	schedule (of that coroutine). This is a bug that will be fixed in
218	some future version.
219
220	$newprio = $coroutine->nice ($change)
221	Similar to "prio", but subtract the given value from the priority
222	(i.e. higher values mean lower priority, just as in unix).
223
224	$olddesc = $coroutine->desc ($newdesc)
225	Sets (or gets in case the argument is missing) the description for
226	this coroutine. This is just a free-form string you can associate
227	with a coroutine.
228
229	This method simply sets the "$coroutine->{desc}" member to the given
230	string. You can modify this member directly if you wish.
231
232	$coroutine->throw ([$scalar])
233	If $throw is specified and defined, it will be thrown as an
234	exception inside the coroutine at the next convinient point in time
235	(usually after it gains control at the next schedule/transfer/cede).
236	Otherwise clears the exception object.
237
238	The exception object will be thrown "as is" with the specified
239	scalar in $@, i.e. if it is a string, no line number or newline will
240	be appended (unlike with "die").
241
242	This can be used as a softer means than "cancel" to ask a coroutine
243	to end itself, although there is no guarentee that the exception
244	will lead to termination, and if the exception isn't caught it might
245	well end the whole program.
246
247	GLOBAL FUNCTIONS
248	Coro::nready
249	Returns the number of coroutines that are currently in the ready
250	state, i.e. that can be switched to. The value 0 means that the only
251	runnable coroutine is the currently running one, so "cede" would
252	have no effect, and "schedule" would cause a deadlock unless there
253	is an idle handler that wakes up some coroutines.
254
255	my $guard = Coro::guard { ... }
256	This creates and returns a guard object. Nothing happens until the
257	object gets destroyed, in which case the codeblock given as argument
258	will be executed. This is useful to free locks or other resources in
259	case of a runtime error or when the coroutine gets canceled, as in
260	both cases the guard block will be executed. The guard object
261	supports only one method, "->cancel", which will keep the codeblock
262	from being executed.
263
264	Example: set some flag and clear it again when the coroutine gets
265	canceled or the function returns:
266
267	sub do_something {
268	my $guard = Coro::guard { $busy = 0 };
269	$busy = 1;
270
271	# do something that requires $busy to be true
272	}
273
274	unblock_sub { ... }
275	This utility function takes a BLOCK or code reference and "unblocks"
276	it, returning the new coderef. This means that the new coderef will
277	return immediately without blocking, returning nothing, while the
278	original code ref will be called (with parameters) from within its
279	own coroutine.
280
281	The reason this function exists is that many event libraries (such
282	as the venerable Event module) are not coroutine-safe (a weaker form
283	of thread-safety). This means you must not block within event
284	callbacks, otherwise you might suffer from crashes or worse.
285
286	This function allows your callbacks to block by executing them in
287	another coroutine where it is safe to block. One example where
288	blocking is handy is when you use the Coro::AIO functions to save
289	results to disk.
290
291	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
292	when creating event callbacks that want to block.
293
294	BUGS/LIMITATIONS
295	- you must make very sure that no coro is still active on global
296	destruction. very bad things might happen otherwise (usually segfaults).
297
298	- this module is not thread-safe. You should only ever use this module
299	from the same thread (this requirement might be loosened in the future
300	to allow per-thread schedulers, but Coro::State does not yet allow
301	this).
302
303	SEE ALSO
304	Support/Utility: Coro::Specific, Coro::State, Coro::Util.
305
306	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
307	Coro::SemaphoreSet, Coro::RWLock.
308
309	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,
310	Coro::Select.
311
312	Embedding: <Coro:MakeMaker>
313
314	AUTHOR
315	Marc Lehmann <schmorp@schmorp.de>
316	http://home.schmorp.de/
317