[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.

        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, otherwise the
        coroutine will be re-used "as-is".

        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).

    # 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" for additional discussion.

    $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 multiple
        times from multiple coroutine.

    $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.

  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::Cont, 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:	1.9
Committed:	Sat Sep 29 19:42:08 2007 UTC (16 years, 7 months ago) by root
Branch:	MAIN
Changes since 1.8:	+3 -1 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	Calling "exit" in a coroutine will do the same as calling exit
72	outside the coroutine. Likewise, when the coroutine dies, the
73	program will exit, just as it would in the main program.
74
75	# create a new coroutine that just prints its arguments
76	async {
77	print "@_\n";
78	} 1,2,3,4;
79
80	async_pool { ... } [@args...]
81	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
83	coroutine that might have executed other code already (which can be
84	good or bad :).
85
86	Also, the block is executed in an "eval" context and a warning will
87	be issued in case of an exception instead of terminating the
88	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
90	terminate or cancel, which somehow defeats the purpose of pooling.
91
92	The priority will be reset to 0 after each job, otherwise the
93	coroutine will be re-used "as-is".
94
95	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
97	coros as required.
98
99	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.
101	"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
103	grows larger than 16kb (adjustable with $Coro::POOL_RSS) it will
104	also exit.
105
106	schedule
107	Calls the scheduler. Please note that the current coroutine will not
108	be put into the ready queue, so calling this function usually means
109	you will never be called again unless something else (e.g. an event
110	handler) calls ready.
111
112	The canonical way to wait on external events is this:
113
114	{
115	# remember current coroutine
116	my $current = $Coro::current;
117
118	# register a hypothetical event handler
119	on_event_invoke sub {
120	# wake up sleeping coroutine
121	$current->ready;
122	undef $current;
123	};
124
125	# call schedule until event occurred.
126	# in case we are woken up for other reasons
127	# (current still defined), loop.
128	Coro::schedule while $current;
129	}
130
131	cede
132	"Cede" to other coroutines. This function puts the current coroutine
133	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
135	higher priority.
136
137	Returns true if at least one coroutine switch has happened.
138
139	Coro::cede_notself
140	Works like cede, but is not exported by default and will cede to any
141	coroutine, regardless of priority, once.
142
143	Returns true if at least one coroutine switch has happened.
144
145	terminate [arg...]
146	Terminates the current coroutine with the given status values (see
147	cancel).
148
149	# dynamic methods
150
151	COROUTINE METHODS
152	These are the methods you can call on coroutine objects.
153
154	new Coro \&sub [, @args...]
155	Create a new coroutine and return it. When the sub returns the
156	coroutine automatically terminates as if "terminate" with the
157	returned values were called. To make the coroutine run you must
158	first put it into the ready queue by calling the ready method.
159
160	See "async" for additional discussion.
161
162	$success = $coroutine->ready
163	Put the given coroutine into the ready queue (according to it's
164	priority) and return true. If the coroutine is already in the ready
165	queue, do nothing and return false.
166
167	$is_ready = $coroutine->is_ready
168	Return wether the coroutine is currently the ready queue or not,
169
170	$coroutine->cancel (arg...)
171	Terminates the given coroutine and makes it return the given
172	arguments as status (default: the empty list). Never returns if the
173	coroutine is the current coroutine.
174
175	$coroutine->join
176	Wait until the coroutine terminates and return any values given to
177	the "terminate" or "cancel" functions. "join" can be called multiple
178	times from multiple coroutine.
179
180	$coroutine->on_destroy (\&cb)
181	Registers a callback that is called when this coroutine gets
182	destroyed, but before it is joined. The callback gets passed the
183	terminate arguments, if any.
184
185	$oldprio = $coroutine->prio ($newprio)
186	Sets (or gets, if the argument is missing) the priority of the
187	coroutine. Higher priority coroutines get run before lower priority
188	coroutines. Priorities are small signed integers (currently -4 ..
189	+3), that you can refer to using PRIO_xxx constants (use the import
190	tag :prio to get then):
191
192	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
193	3 > 1 > 0 > -1 > -3 > -4
194
195	# set priority to HIGH
196	current->prio(PRIO_HIGH);
197
198	The idle coroutine ($Coro::idle) always has a lower priority than
199	any existing coroutine.
200
201	Changing the priority of the current coroutine will take effect
202	immediately, but changing the priority of coroutines in the ready
203	queue (but not running) will only take effect after the next
204	schedule (of that coroutine). This is a bug that will be fixed in
205	some future version.
206
207	$newprio = $coroutine->nice ($change)
208	Similar to "prio", but subtract the given value from the priority
209	(i.e. higher values mean lower priority, just as in unix).
210
211	$olddesc = $coroutine->desc ($newdesc)
212	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
214	with a coroutine.
215
216	GLOBAL FUNCTIONS
217	Coro::nready
218	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
220	runnable coroutine is the currently running one, so "cede" would
221	have no effect, and "schedule" would cause a deadlock unless there
222	is an idle handler that wakes up some coroutines.
223
224	my $guard = Coro::guard { ... }
225	This creates and returns a guard object. Nothing happens until the
226	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
228	case of a runtime error or when the coroutine gets canceled, as in
229	both cases the guard block will be executed. The guard object
230	supports only one method, "->cancel", which will keep the codeblock
231	from being executed.
232
233	Example: set some flag and clear it again when the coroutine gets
234	canceled or the function returns:
235
236	sub do_something {
237	my $guard = Coro::guard { $busy = 0 };
238	$busy = 1;
239
240	# do something that requires $busy to be true
241	}
242
243	unblock_sub { ... }
244	This utility function takes a BLOCK or code reference and "unblocks"
245	it, returning the new coderef. This means that the new coderef will
246	return immediately without blocking, returning nothing, while the
247	original code ref will be called (with parameters) from within its
248	own coroutine.
249
250	The reason this function exists is that many event libraries (such
251	as the venerable Event module) are not coroutine-safe (a weaker form
252	of thread-safety). This means you must not block within event
253	callbacks, otherwise you might suffer from crashes or worse.
254
255	This function allows your callbacks to block by executing them in
256	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
258	results to disk.
259
260	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
261	when creating event callbacks that want to block.
262
263	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
268	from the same thread (this requirement might be loosened in the future
269	to allow per-thread schedulers, but Coro::State does not yet allow
270	this).
271
272	SEE ALSO
273	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.
274
275	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
276	Coro::SemaphoreSet, Coro::RWLock.
277
278	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,
279	Coro::Select.
280
281	Embedding: <Coro:MakeMaker>
282
283	AUTHOR
284	Marc Lehmann <schmorp@schmorp.de>
285	http://home.schmorp.de/
286