[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 not work correctly, so do not do
        that.

        When the coroutine dies, the program will exit, just as 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.

        Calling "exit" in a coroutine will not work correctly, so do not do
        that.

    $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
        objetc 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:	1.6
Committed:	Sat Jan 6 02:45:56 2007 UTC (17 years, 4 months ago) by root
Branch:	MAIN
CVS Tags:	rel-3_41, rel-3_55, rel-3_51, rel-3_6, rel-3_4, rel-3_5, rel-3_3, rel-3_501
Changes since 1.5:	+58 -1 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	1.4	Calling "exit" in a coroutine will not work correctly, so do not do
72			that.
73
74	root	1.3	When the coroutine dies, the program will exit, just as in the main
75			program.
76
77	root	1.1	# create a new coroutine that just prints its arguments
78			async {
79			print "@_\n";
80			} 1,2,3,4;
81
82	root	1.6	async_pool { ... } [@args...]
83			Similar to "async", but uses a coroutine pool, so you should not
84			call terminate or join (although you are allowed to), and you get a
85			coroutine that might have executed other code already (which can be
86			good or bad :).
87
88			Also, the block is executed in an "eval" context and a warning will
89			be issued in case of an exception instead of terminating the
90			program, as "async" does. As the coroutine is being reused, stuff
91			like "on_destroy" will not work in the expected way, unless you call
92			terminate or cancel, which somehow defeats the purpose of pooling.
93
94			The priority will be reset to 0 after each job, otherwise the
95			coroutine will be re-used "as-is".
96
97			The pool size is limited to 8 idle coroutines (this can be adjusted
98			by changing $Coro::POOL_SIZE), and there can be as many non-idle
99			coros as required.
100
101			If you are concerned about pooled coroutines growing a lot because a
102			single "async_pool" used a lot of stackspace you can e.g.
103			"async_pool { terminate }" once per second or so to slowly replenish
104			the pool.
105
106	root	1.1	schedule
107	root	1.4	Calls the scheduler. Please note that the current coroutine will not
108	root	1.1	be put into the ready queue, so calling this function usually means
109	root	1.4	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 occured.
126			# in case we are woken up for other reasons
127			# (current still defined), loop.
128			Coro::schedule while $current;
129			}
130	root	1.1
131			cede
132	root	1.4	"Cede" to other coroutines. This function puts the current coroutine
133	root	1.1	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	root	1.6	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	root	1.1	terminate [arg...]
146	root	1.4	Terminates the current coroutine with the given status values (see
147	root	1.1	cancel).
148
149			# dynamic methods
150
151	root	1.4	COROUTINE METHODS
152			These are the methods you can call on coroutine objects.
153	root	1.1
154			new Coro \&sub [, @args...]
155	root	1.4	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			Calling "exit" in a coroutine will not work correctly, so do not do
161			that.
162
163			$success = $coroutine->ready
164			Put the given coroutine into the ready queue (according to it's
165			priority) and return true. If the coroutine is already in the ready
166			queue, do nothing and return false.
167
168			$is_ready = $coroutine->is_ready
169			Return wether the coroutine is currently the ready queue or not,
170
171			$coroutine->cancel (arg...)
172			Terminates the given coroutine and makes it return the given
173	root	1.6	arguments as status (default: the empty list). Never returns if the
174			coroutine is the current coroutine.
175	root	1.1
176	root	1.4	$coroutine->join
177	root	1.1	Wait until the coroutine terminates and return any values given to
178			the "terminate" or "cancel" functions. "join" can be called multiple
179	root	1.4	times from multiple coroutine.
180	root	1.1
181	root	1.6	$coroutine->on_destroy (\&cb)
182			Registers a callback that is called when this coroutine gets
183			destroyed, but before it is joined. The callback gets passed the
184			terminate arguments, if any.
185
186	root	1.4	$oldprio = $coroutine->prio ($newprio)
187	root	1.1	Sets (or gets, if the argument is missing) the priority of the
188	root	1.4	coroutine. Higher priority coroutines get run before lower priority
189			coroutines. Priorities are small signed integers (currently -4 ..
190	root	1.1	+3), that you can refer to using PRIO_xxx constants (use the import
191			tag :prio to get then):
192
193			PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
194			3 > 1 > 0 > -1 > -3 > -4
195
196			# set priority to HIGH
197			current->prio(PRIO_HIGH);
198
199			The idle coroutine ($Coro::idle) always has a lower priority than
200			any existing coroutine.
201
202	root	1.4	Changing the priority of the current coroutine will take effect
203			immediately, but changing the priority of coroutines in the ready
204	root	1.1	queue (but not running) will only take effect after the next
205	root	1.4	schedule (of that coroutine). This is a bug that will be fixed in
206			some future version.
207	root	1.1
208	root	1.4	$newprio = $coroutine->nice ($change)
209	root	1.1	Similar to "prio", but subtract the given value from the priority
210			(i.e. higher values mean lower priority, just as in unix).
211
212	root	1.4	$olddesc = $coroutine->desc ($newdesc)
213	root	1.1	Sets (or gets in case the argument is missing) the description for
214	root	1.4	this coroutine. This is just a free-form string you can associate
215			with a coroutine.
216
217	root	1.5	GLOBAL FUNCTIONS
218			Coro::nready
219			Returns the number of coroutines that are currently in the ready
220			state, i.e. that can be swicthed to. The value 0 means that the only
221			runnable coroutine is the currently running one, so "cede" would
222			have no effect, and "schedule" would cause a deadlock unless there
223			is an idle handler that wakes up some coroutines.
224
225	root	1.6	my $guard = Coro::guard { ... }
226			This creates and returns a guard object. Nothing happens until the
227			objetc gets destroyed, in which case the codeblock given as argument
228			will be executed. This is useful to free locks or other resources in
229			case of a runtime error or when the coroutine gets canceled, as in
230			both cases the guard block will be executed. The guard object
231			supports only one method, "->cancel", which will keep the codeblock
232			from being executed.
233
234			Example: set some flag and clear it again when the coroutine gets
235			canceled or the function returns:
236
237			sub do_something {
238			my $guard = Coro::guard { $busy = 0 };
239			$busy = 1;
240
241			# do something that requires $busy to be true
242			}
243
244	root	1.4	unblock_sub { ... }
245			This utility function takes a BLOCK or code reference and "unblocks"
246			it, returning the new coderef. This means that the new coderef will
247			return immediately without blocking, returning nothing, while the
248			original code ref will be called (with parameters) from within its
249			own coroutine.
250
251			The reason this fucntion exists is that many event libraries (such
252			as the venerable Event module) are not coroutine-safe (a weaker form
253			of thread-safety). This means you must not block within event
254			callbacks, otherwise you might suffer from crashes or worse.
255
256			This function allows your callbacks to block by executing them in
257			another coroutine where it is safe to block. One example where
258			blocking is handy is when you use the Coro::AIO functions to save
259			results to disk.
260
261			In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
262			when creating event callbacks that want to block.
263	root	1.1
264			BUGS/LIMITATIONS
265			- you must make very sure that no coro is still active on global
266			destruction. very bad things might happen otherwise (usually segfaults).
267
268			- this module is not thread-safe. You should only ever use this module
269			from the same thread (this requirement might be losened in the future
270			to allow per-thread schedulers, but Coro::State does not yet allow
271			this).
272
273			SEE ALSO
274	root	1.2	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.
275
276			Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
277			Coro::SemaphoreSet, Coro::RWLock.
278
279			Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,
280			Coro::Select.
281
282			Embedding: <Coro:MakeMaker>
283	root	1.1
284			AUTHOR
285			Marc Lehmann <schmorp@schmorp.de>
286			http://home.schmorp.de/
287