[ViewVC] Annotation 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 *
#	User	Rev	Content
1	root	1.1	NAME
2			Coro - coroutine process abstraction
3
4			SYNOPSIS
5			use Coro;
6
7			async {
8			# some asynchronous thread of execution
9			};
10
11	root	1.4	# alternatively create an async coroutine like this:
12	root	1.1
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	root	1.5	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	root	1.1
33			In this module, coroutines are defined as "callchain + lexical variables
34	root	1.5	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
35			callchain, its own set of lexicals and its own set of perls most
36	root	1.1	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	root	1.4	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	root	1.1	$idle
50	root	1.4	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	root	1.1
62			STATIC METHODS
63			Static methods are actually functions that operate on the current
64	root	1.4	coroutine only.
65	root	1.1
66			async { ... } [@args...]
67	root	1.4	Create a new asynchronous coroutine and return it's coroutine object
68			(usually unused). When the sub returns the new coroutine is
69	root	1.1	automatically terminated.
70
71	root	1.7	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	root	1.3
75	root	1.1	# create a new coroutine that just prints its arguments
76			async {
77			print "@_\n";
78			} 1,2,3,4;
79
80	root	1.6	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	root	1.1	schedule
105	root	1.4	Calls the scheduler. Please note that the current coroutine will not
106	root	1.1	be put into the ready queue, so calling this function usually means
107	root	1.4	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	root	1.1
129			cede
130	root	1.4	"Cede" to other coroutines. This function puts the current coroutine
131	root	1.1	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	root	1.6	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	root	1.1	terminate [arg...]
144	root	1.4	Terminates the current coroutine with the given status values (see
145	root	1.1	cancel).
146
147			# dynamic methods
148
149	root	1.4	COROUTINE METHODS
150			These are the methods you can call on coroutine objects.
151	root	1.1
152			new Coro \&sub [, @args...]
153	root	1.4	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	root	1.7	See "async" for additional discussion.
159	root	1.4
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	root	1.6	arguments as status (default: the empty list). Never returns if the
171			coroutine is the current coroutine.
172	root	1.1
173	root	1.4	$coroutine->join
174	root	1.1	Wait until the coroutine terminates and return any values given to
175			the "terminate" or "cancel" functions. "join" can be called multiple
176	root	1.4	times from multiple coroutine.
177	root	1.1
178	root	1.6	$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	root	1.4	$oldprio = $coroutine->prio ($newprio)
184	root	1.1	Sets (or gets, if the argument is missing) the priority of the
185	root	1.4	coroutine. Higher priority coroutines get run before lower priority
186			coroutines. Priorities are small signed integers (currently -4 ..
187	root	1.1	+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	root	1.4	Changing the priority of the current coroutine will take effect
200			immediately, but changing the priority of coroutines in the ready
201	root	1.1	queue (but not running) will only take effect after the next
202	root	1.4	schedule (of that coroutine). This is a bug that will be fixed in
203			some future version.
204	root	1.1
205	root	1.4	$newprio = $coroutine->nice ($change)
206	root	1.1	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	root	1.4	$olddesc = $coroutine->desc ($newdesc)
210	root	1.1	Sets (or gets in case the argument is missing) the description for
211	root	1.4	this coroutine. This is just a free-form string you can associate
212			with a coroutine.
213
214	root	1.5	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	root	1.6	my $guard = Coro::guard { ... }
223			This creates and returns a guard object. Nothing happens until the
224	root	1.7	object gets destroyed, in which case the codeblock given as argument
225	root	1.6	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	root	1.4	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	root	1.1
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	root	1.2	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	root	1.1
281			AUTHOR
282			Marc Lehmann <schmorp@schmorp.de>
283			http://home.schmorp.de/
284