[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;

    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.

    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).

    $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.

    $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.

    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:	1.5
Committed:	Mon Dec 4 22:06:02 2006 UTC (17 years, 5 months ago) by root
Branch:	MAIN
CVS Tags:	rel-3_1, rel-3_2, rel-3_11
Changes since 1.4:	+21 -4 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			schedule
83	root	1.4	Calls the scheduler. Please note that the current coroutine will not
84	root	1.1	be put into the ready queue, so calling this function usually means
85	root	1.4	you will never be called again unless something else (e.g. an event
86			handler) calls ready.
87
88			The canonical way to wait on external events is this:
89
90			{
91			# remember current coroutine
92			my $current = $Coro::current;
93
94			# register a hypothetical event handler
95			on_event_invoke sub {
96			# wake up sleeping coroutine
97			$current->ready;
98			undef $current;
99			};
100
101			# call schedule until event occured.
102			# in case we are woken up for other reasons
103			# (current still defined), loop.
104			Coro::schedule while $current;
105			}
106	root	1.1
107			cede
108	root	1.4	"Cede" to other coroutines. This function puts the current coroutine
109	root	1.1	into the ready queue and calls "schedule", which has the effect of
110			giving up the current "timeslice" to other coroutines of the same or
111			higher priority.
112
113			terminate [arg...]
114	root	1.4	Terminates the current coroutine with the given status values (see
115	root	1.1	cancel).
116
117			# dynamic methods
118
119	root	1.4	COROUTINE METHODS
120			These are the methods you can call on coroutine objects.
121	root	1.1
122			new Coro \&sub [, @args...]
123	root	1.4	Create a new coroutine and return it. When the sub returns the
124			coroutine automatically terminates as if "terminate" with the
125			returned values were called. To make the coroutine run you must
126			first put it into the ready queue by calling the ready method.
127
128			Calling "exit" in a coroutine will not work correctly, so do not do
129			that.
130
131			$success = $coroutine->ready
132			Put the given coroutine into the ready queue (according to it's
133			priority) and return true. If the coroutine is already in the ready
134			queue, do nothing and return false.
135
136			$is_ready = $coroutine->is_ready
137			Return wether the coroutine is currently the ready queue or not,
138
139			$coroutine->cancel (arg...)
140			Terminates the given coroutine and makes it return the given
141			arguments as status (default: the empty list).
142	root	1.1
143	root	1.4	$coroutine->join
144	root	1.1	Wait until the coroutine terminates and return any values given to
145			the "terminate" or "cancel" functions. "join" can be called multiple
146	root	1.4	times from multiple coroutine.
147	root	1.1
148	root	1.4	$oldprio = $coroutine->prio ($newprio)
149	root	1.1	Sets (or gets, if the argument is missing) the priority of the
150	root	1.4	coroutine. Higher priority coroutines get run before lower priority
151			coroutines. Priorities are small signed integers (currently -4 ..
152	root	1.1	+3), that you can refer to using PRIO_xxx constants (use the import
153			tag :prio to get then):
154
155			PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
156			3 > 1 > 0 > -1 > -3 > -4
157
158			# set priority to HIGH
159			current->prio(PRIO_HIGH);
160
161			The idle coroutine ($Coro::idle) always has a lower priority than
162			any existing coroutine.
163
164	root	1.4	Changing the priority of the current coroutine will take effect
165			immediately, but changing the priority of coroutines in the ready
166	root	1.1	queue (but not running) will only take effect after the next
167	root	1.4	schedule (of that coroutine). This is a bug that will be fixed in
168			some future version.
169	root	1.1
170	root	1.4	$newprio = $coroutine->nice ($change)
171	root	1.1	Similar to "prio", but subtract the given value from the priority
172			(i.e. higher values mean lower priority, just as in unix).
173
174	root	1.4	$olddesc = $coroutine->desc ($newdesc)
175	root	1.1	Sets (or gets in case the argument is missing) the description for
176	root	1.4	this coroutine. This is just a free-form string you can associate
177			with a coroutine.
178
179	root	1.5	GLOBAL FUNCTIONS
180			Coro::nready
181			Returns the number of coroutines that are currently in the ready
182			state, i.e. that can be swicthed to. The value 0 means that the only
183			runnable coroutine is the currently running one, so "cede" would
184			have no effect, and "schedule" would cause a deadlock unless there
185			is an idle handler that wakes up some coroutines.
186
187	root	1.4	unblock_sub { ... }
188			This utility function takes a BLOCK or code reference and "unblocks"
189			it, returning the new coderef. This means that the new coderef will
190			return immediately without blocking, returning nothing, while the
191			original code ref will be called (with parameters) from within its
192			own coroutine.
193
194			The reason this fucntion exists is that many event libraries (such
195			as the venerable Event module) are not coroutine-safe (a weaker form
196			of thread-safety). This means you must not block within event
197			callbacks, otherwise you might suffer from crashes or worse.
198
199			This function allows your callbacks to block by executing them in
200			another coroutine where it is safe to block. One example where
201			blocking is handy is when you use the Coro::AIO functions to save
202			results to disk.
203
204			In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
205			when creating event callbacks that want to block.
206	root	1.1
207			BUGS/LIMITATIONS
208			- you must make very sure that no coro is still active on global
209			destruction. very bad things might happen otherwise (usually segfaults).
210
211			- this module is not thread-safe. You should only ever use this module
212			from the same thread (this requirement might be losened in the future
213			to allow per-thread schedulers, but Coro::State does not yet allow
214			this).
215
216			SEE ALSO
217	root	1.2	Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util.
218
219			Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
220			Coro::SemaphoreSet, Coro::RWLock.
221
222			Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket,
223			Coro::Select.
224
225			Embedding: <Coro:MakeMaker>
226	root	1.1
227			AUTHOR
228			Marc Lehmann <schmorp@schmorp.de>
229			http://home.schmorp.de/
230