[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 use din this module also guarentees 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 essentiel 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.

    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 occured.
              # 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 swicthed 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 fucntion 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 losened 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:	1.7
Committed:	Mon Apr 16 13:26:43 2007 UTC (17 years, 1 month ago) by root
Branch:	MAIN
Changes since 1.6:	+5 -8 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 use din this module also guarentees 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 essentiel 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.
103
104	schedule
105	Calls the scheduler. Please note that the current coroutine will not
106	be put into the ready queue, so calling this function usually means
107	you will never be called again unless something else (e.g. an event
108	handler) calls ready.
109
110	The canonical way to wait on external events is this:
111
112	{
113	# remember current coroutine
114	my $current = $Coro::current;
115
116	# register a hypothetical event handler
117	on_event_invoke sub {
118	# wake up sleeping coroutine
119	$current->ready;
120	undef $current;
121	};
122
123	# call schedule until event occured.
124	# in case we are woken up for other reasons
125	# (current still defined), loop.
126	Coro::schedule while $current;
127	}
128
129	cede
130	"Cede" to other coroutines. This function puts the current coroutine
131	into the ready queue and calls "schedule", which has the effect of
132	giving up the current "timeslice" to other coroutines of the same or
133	higher priority.
134
135	Returns true if at least one coroutine switch has happened.
136
137	Coro::cede_notself
138	Works like cede, but is not exported by default and will cede to any
139	coroutine, regardless of priority, once.
140
141	Returns true if at least one coroutine switch has happened.
142
143	terminate [arg...]
144	Terminates the current coroutine with the given status values (see
145	cancel).
146
147	# dynamic methods
148
149	COROUTINE METHODS
150	These are the methods you can call on coroutine objects.
151
152	new Coro \&sub [, @args...]
153	Create a new coroutine and return it. When the sub returns the
154	coroutine automatically terminates as if "terminate" with the
155	returned values were called. To make the coroutine run you must
156	first put it into the ready queue by calling the ready method.
157
158	See "async" for additional discussion.
159
160	$success = $coroutine->ready
161	Put the given coroutine into the ready queue (according to it's
162	priority) and return true. If the coroutine is already in the ready
163	queue, do nothing and return false.
164
165	$is_ready = $coroutine->is_ready
166	Return wether the coroutine is currently the ready queue or not,
167
168	$coroutine->cancel (arg...)
169	Terminates the given coroutine and makes it return the given
170	arguments as status (default: the empty list). Never returns if the
171	coroutine is the current coroutine.
172
173	$coroutine->join
174	Wait until the coroutine terminates and return any values given to
175	the "terminate" or "cancel" functions. "join" can be called multiple
176	times from multiple coroutine.
177
178	$coroutine->on_destroy (\&cb)
179	Registers a callback that is called when this coroutine gets
180	destroyed, but before it is joined. The callback gets passed the
181	terminate arguments, if any.
182
183	$oldprio = $coroutine->prio ($newprio)
184	Sets (or gets, if the argument is missing) the priority of the
185	coroutine. Higher priority coroutines get run before lower priority
186	coroutines. Priorities are small signed integers (currently -4 ..
187	+3), that you can refer to using PRIO_xxx constants (use the import
188	tag :prio to get then):
189
190	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
191	3 > 1 > 0 > -1 > -3 > -4
192
193	# set priority to HIGH
194	current->prio(PRIO_HIGH);
195
196	The idle coroutine ($Coro::idle) always has a lower priority than
197	any existing coroutine.
198
199	Changing the priority of the current coroutine will take effect
200	immediately, but changing the priority of coroutines in the ready
201	queue (but not running) will only take effect after the next
202	schedule (of that coroutine). This is a bug that will be fixed in
203	some future version.
204
205	$newprio = $coroutine->nice ($change)
206	Similar to "prio", but subtract the given value from the priority
207	(i.e. higher values mean lower priority, just as in unix).
208
209	$olddesc = $coroutine->desc ($newdesc)
210	Sets (or gets in case the argument is missing) the description for
211	this coroutine. This is just a free-form string you can associate
212	with a coroutine.
213
214	GLOBAL FUNCTIONS
215	Coro::nready
216	Returns the number of coroutines that are currently in the ready
217	state, i.e. that can be swicthed to. The value 0 means that the only
218	runnable coroutine is the currently running one, so "cede" would
219	have no effect, and "schedule" would cause a deadlock unless there
220	is an idle handler that wakes up some coroutines.
221
222	my $guard = Coro::guard { ... }
223	This creates and returns a guard object. Nothing happens until the
224	object gets destroyed, in which case the codeblock given as argument
225	will be executed. This is useful to free locks or other resources in
226	case of a runtime error or when the coroutine gets canceled, as in
227	both cases the guard block will be executed. The guard object
228	supports only one method, "->cancel", which will keep the codeblock
229	from being executed.
230
231	Example: set some flag and clear it again when the coroutine gets
232	canceled or the function returns:
233
234	sub do_something {
235	my $guard = Coro::guard { $busy = 0 };
236	$busy = 1;
237
238	# do something that requires $busy to be true
239	}
240
241	unblock_sub { ... }
242	This utility function takes a BLOCK or code reference and "unblocks"
243	it, returning the new coderef. This means that the new coderef will
244	return immediately without blocking, returning nothing, while the
245	original code ref will be called (with parameters) from within its
246	own coroutine.
247
248	The reason this fucntion exists is that many event libraries (such
249	as the venerable Event module) are not coroutine-safe (a weaker form
250	of thread-safety). This means you must not block within event
251	callbacks, otherwise you might suffer from crashes or worse.
252
253	This function allows your callbacks to block by executing them in
254	another coroutine where it is safe to block. One example where
255	blocking is handy is when you use the Coro::AIO functions to save
256	results to disk.
257
258	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
259	when creating event callbacks that want to block.
260
261	BUGS/LIMITATIONS
262	- you must make very sure that no coro is still active on global
263	destruction. very bad things might happen otherwise (usually segfaults).
264
265	- this module is not thread-safe. You should only ever use this module
266	from the same thread (this requirement might be losened in the future
267	to allow per-thread schedulers, but Coro::State does not yet allow
268	this).
269
270	SEE ALSO
271	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.
272
273	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
274	Coro::SemaphoreSet, Coro::RWLock.
275
276	Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,
277	Coro::Select.
278
279	Embedding: <Coro:MakeMaker>
280
281	AUTHOR
282	Marc Lehmann <schmorp@schmorp.de>
283	http://home.schmorp.de/
284