[ViewVC] Contents of: cvs/Coro/README

NAME
    Coro - coroutine process abstraction

SYNOPSIS
      use Coro;
      
  async {
         # some asynchronous thread of execution
         print "2\n";
         cede; # yield back to main
         print "4\n";
      };
      print "1\n";
      cede; # yield to coroutine
      print "3\n";
      cede; # and again
      
  # use locking
      use Coro::Semaphore;
      my $lock = new Coro::Semaphore;
      my $locked;
      
  $lock->down;
      $locked = 1;
      $lock->up;

DESCRIPTION
    This module collection manages coroutines. Coroutines are similar to
    threads but don't (in general) 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 and easier than threads programming.

    Unlike a normal perl program, however, coroutines allow you to have
    multiple running interpreters that share data, which is especially
    useful to code pseudo-parallel processes and for event-based
    programming, such as multiple HTTP-GET requests running concurrently.
    See Coro::AnyEvent to learn more.

    Coroutines are also useful because Perl has no support for threads (the
    so called "threads" that perl offers are nothing more than the (bad)
    process emulation coming from the Windows platform: On standard
    operating systems they serve no purpose whatsoever, except by making
    your programs slow and making them use a lot of memory. Best disable
    them when building perl, or aks your software vendor/distributor to do
    it for you).

    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 (see Coro::State for more configuration).

    $Coro::main
        This variable stores the coroutine object that represents the main
        program. While you cna "ready" it and do most other things you can
        do to coroutines, it is mainly useful to compare again
        $Coro::current, to see whether you are running in the main program
        or not.

    $Coro::current
        The coroutine object representing the current coroutine (the last
        coroutine that the Coro scheduler switched to). The initial value is
        $main (of course).

        This variable is strictly *read-only*. You can take copies of the
        value stored in it and use it as any other coroutine object, but you
        must not otherwise modify the variable itself.

    $Coro::idle
        This variable is mainly useful to integrate Coro into event loops.
        It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as
        this is pretty low-level functionality.

        This variable stores 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::AnyEvent" to wait on an external event that hopefully wake up
        a coroutine so the scheduler can run it.

        Note that the callback *must not*, under any circumstances, block
        the current coroutine. Normally, this is achieved by having an "idle
        coroutine" that calls the event loop and then blocks again, and then
        readying that coroutine in the idle handler.

        See Coro::Event or Coro::AnyEvent for examples of using this
        technique.

        Please note that if your callback recursively invokes perl (e.g. for
        event handlers), then it must be prepared to be called recursively
        itself.

  SIMPLE COROUTINE CREATION
    async { ... } [@args...]
        Create a new coroutine and return it's coroutine object (usually
        unused). The coroutine will be put into the ready queue, so it will
        start running automatically on the next scheduler run.

        The first argument is a codeblock/closure that should be executed in
        the coroutine. When it returns argument returns the coroutine is
        automatically terminated.

        The remaining arguments are passed as arguments to the closure.

        See the "Coro::State::new" constructor for info about the coroutine
        environment in which coroutines are executed.

        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.

        If you do not want that, you can provide a default "die" handler, or
        simply avoid dieing (by use of "eval").

        Example: 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 on it (although you are allowed to), and you
        get a coroutine that might have executed other code already (which
        can be good or bad :).

        On the plus side, this function is faster than creating (and
        destroying) a completely new coroutine, so if you need a lot of
        generic coroutines in quick successsion, use "async_pool", not
        "async".

        The code 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
        (but is fine in the exceptional case).

        The priority will be reset to 0 after each run, tracing will be
        disabled, the description will be reset and the default output
        filehandle gets restored, so you can change all these. Otherwise the
        coroutine will be re-used "as-is": most notably if you change other
        per-coroutine global stuff such as $/ you *must needs* to revert
        that change, which is most simply done by using local as in: " local
        $/ ".

        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 via $Coro::POOL_RSS) it will also
        be destroyed.

  STATIC METHODS
    Static methods are actually functions that operate on the current
    coroutine.

    schedule
        Calls the scheduler. The scheduler will find the next coroutine that
        is to be run from the ready queue and switches to it. The next
        coroutine to be run is simply the one with the highest priority that
        is longest in its ready queue. If there is no coroutine ready, it
        will clal the $Coro::idle hook.

        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", thus waking you up.

        This makes "schedule" *the* generic method to use to block the
        current coroutine and wait for events: first you remember the
        current coroutine in a variable, then arrange for some callback of
        yours to call "->ready" on that once some event happens, and last
        you call "schedule" to put yourself to sleep. Note that a lot of
        things can wake your coroutine up, so you need to check whether the
        event indeed happened, e.g. by storing the status in a variable.

        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. Once your coroutine gets its turn again it will
        automatically be resumed.

        This function is often called "yield" in other languages.

    Coro::cede_notself
        Works like cede, but is not exported by default and will cede to
        *any* coroutine, regardless of priority. This is useful sometimes to
        ensure progress is made.

    terminate [arg...]
        Terminates the current coroutine with the given status values (see
        cancel).

    killall
        Kills/terminates/cancels all coroutines except the currently running
        one. This is useful after a fork, either in the child or the parent,
        as usually only one of them should inherit the running coroutines.

        Note that while this will try to free some of the main programs
        resources, you cannot free all of them, so if a coroutine that is
        not the main program calls this function, there will be some
        one-time resource leak.

  COROUTINE METHODS
    These are the methods you can call on coroutine objects (or to create
    them).

    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" and "Coro::State::new" for additional info about the
        coroutine environment.

    $success = $coroutine->ready
        Put the given coroutine into the end of its ready queue (there is
        one queue for each priority) and return true. If the coroutine is
        already in the ready queue, do nothing and return false.

        This ensures that the scheduler will resume this coroutine
        automatically once all the coroutines of higher priority and all
        coroutines of the same priority that were put into the ready queue
        earlier have been resumed.

    $is_ready = $coroutine->is_ready
        Return whether 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
        concurrently from multiple coroutines, and all will be resumed and
        given the status return once the $coroutine terminates.

    $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, and *must not* die, under any
        circumstances.

    $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.

        This method simply sets the "$coroutine->{desc}" member to the given
        string. You can modify this member directly if you wish.

    $coroutine->throw ([$scalar])
        If $throw is specified and defined, it will be thrown as an
        exception inside the coroutine at the next convinient point in time
        (usually after it gains control at the next schedule/transfer/cede).
        Otherwise clears the exception object.

        The exception object will be thrown "as is" with the specified
        scalar in $@, i.e. if it is a string, no line number or newline will
        be appended (unlike with "die").

        This can be used as a softer means than "cancel" to ask a coroutine
        to end itself, although there is no guarentee that the exception
        will lead to termination, and if the exception isn't caught it might
        well end the whole program.

  GLOBAL FUNCTIONS
    Coro::nready
        Returns the number of coroutines that are currently in the ready
        state, i.e. that can be switched to by calling "schedule" directory
        or indirectly. 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 a new coderef. Unblocking means that calling the new
        coderef will return immediately without blocking, returning nothing,
        while the original code ref will be called (with parameters) from
        within another 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. The
        only event library currently known that is safe to use without
        "unblock_sub" is EV.

        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, for example.

        In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
        when creating event callbacks that want to block.

        If your handler does not plan to block (e.g. simply sends a message
        to another coroutine, or puts some other coroutine into the ready
        queue), there is no reason to use "unblock_sub".

        Note that you also need to use "unblock_sub" for any other callbacks
        that are indirectly executed by any C-based event loop. For example,
        when you use a module that uses AnyEvent (and you use
        Coro::AnyEvent) and it provides callbacks that are the result of
        some event callback, then you must not block either, or use
        "unblock_sub".

BUGS/LIMITATIONS
    This module is not perl-pseudo-thread-safe. You should only ever use
    this module from the same thread (this requirement might be removed in
    the future to allow per-thread schedulers, but Coro::State does not yet
    allow this). I recommend disabling thread support and using processes,
    as this is much faster and uses less memory.

SEE ALSO
    Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.

    Debugging: Coro::Debug.

    Support/Utility: Coro::Specific, Coro::Util.

    Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
    Coro::SemaphoreSet, Coro::RWLock.

    IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.

    Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.

    XS API: Coro::MakeMaker.

    Low level Configuration, Coroutine Environment: Coro::State.

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/

Revision:	1.15
Committed:	Sun Sep 21 01:23:26 2008 UTC (15 years, 8 months ago) by root
Branch:	MAIN
CVS Tags:	rel-4_748, rel-4_8, rel-4_747, rel-4_479, rel-4_746
Changes since 1.14:	+6 -5 lines
Log Message:	4.746
#	Content
1	NAME
2	Coro - coroutine process abstraction
3
4	SYNOPSIS
5	use Coro;
6
7	async {
8	# some asynchronous thread of execution
9	print "2\n";
10	cede; # yield back to main
11	print "4\n";
12	};
13	print "1\n";
14	cede; # yield to coroutine
15	print "3\n";
16	cede; # and again
17
18	# use locking
19	use Coro::Semaphore;
20	my $lock = new Coro::Semaphore;
21	my $locked;
22
23	$lock->down;
24	$locked = 1;
25	$lock->up;
26
27	DESCRIPTION
28	This module collection manages coroutines. Coroutines are similar to
29	threads but don't (in general) run in parallel at the same time even on
30	SMP machines. The specific flavor of coroutine used in this module also
31	guarantees you that it will not switch between coroutines unless
32	necessary, at easily-identified points in your program, so locking and
33	parallel access are rarely an issue, making coroutine programming much
34	safer and easier than threads programming.
35
36	Unlike a normal perl program, however, coroutines allow you to have
37	multiple running interpreters that share data, which is especially
38	useful to code pseudo-parallel processes and for event-based
39	programming, such as multiple HTTP-GET requests running concurrently.
40	See Coro::AnyEvent to learn more.
41
42	Coroutines are also useful because Perl has no support for threads (the
43	so called "threads" that perl offers are nothing more than the (bad)
44	process emulation coming from the Windows platform: On standard
45	operating systems they serve no purpose whatsoever, except by making
46	your programs slow and making them use a lot of memory. Best disable
47	them when building perl, or aks your software vendor/distributor to do
48	it for you).
49
50	In this module, coroutines are defined as "callchain + lexical variables
51	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
52	callchain, its own set of lexicals and its own set of perls most
53	important global variables (see Coro::State for more configuration).
54
55	$Coro::main
56	This variable stores the coroutine object that represents the main
57	program. While you cna "ready" it and do most other things you can
58	do to coroutines, it is mainly useful to compare again
59	$Coro::current, to see whether you are running in the main program
60	or not.
61
62	$Coro::current
63	The coroutine object representing the current coroutine (the last
64	coroutine that the Coro scheduler switched to). The initial value is
65	$main (of course).
66
67	This variable is strictly read-only. You can take copies of the
68	value stored in it and use it as any other coroutine object, but you
69	must not otherwise modify the variable itself.
70
71	$Coro::idle
72	This variable is mainly useful to integrate Coro into event loops.
73	It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as
74	this is pretty low-level functionality.
75
76	This variable stores a callback that is called whenever the
77	scheduler finds no ready coroutines to run. The default
78	implementation prints "FATAL: deadlock detected" and exits, because
79	the program has no other way to continue.
80
81	This hook is overwritten by modules such as "Coro::Timer" and
82	"Coro::AnyEvent" to wait on an external event that hopefully wake up
83	a coroutine so the scheduler can run it.
84
85	Note that the callback must not, under any circumstances, block
86	the current coroutine. Normally, this is achieved by having an "idle
87	coroutine" that calls the event loop and then blocks again, and then
88	readying that coroutine in the idle handler.
89
90	See Coro::Event or Coro::AnyEvent for examples of using this
91	technique.
92
93	Please note that if your callback recursively invokes perl (e.g. for
94	event handlers), then it must be prepared to be called recursively
95	itself.
96
97	SIMPLE COROUTINE CREATION
98	async { ... } [@args...]
99	Create a new coroutine and return it's coroutine object (usually
100	unused). The coroutine will be put into the ready queue, so it will
101	start running automatically on the next scheduler run.
102
103	The first argument is a codeblock/closure that should be executed in
104	the coroutine. When it returns argument returns the coroutine is
105	automatically terminated.
106
107	The remaining arguments are passed as arguments to the closure.
108
109	See the "Coro::State::new" constructor for info about the coroutine
110	environment in which coroutines are executed.
111
112	Calling "exit" in a coroutine will do the same as calling exit
113	outside the coroutine. Likewise, when the coroutine dies, the
114	program will exit, just as it would in the main program.
115
116	If you do not want that, you can provide a default "die" handler, or
117	simply avoid dieing (by use of "eval").
118
119	Example: Create a new coroutine that just prints its arguments.
120
121	async {
122	print "@_\n";
123	} 1,2,3,4;
124
125	async_pool { ... } [@args...]
126	Similar to "async", but uses a coroutine pool, so you should not
127	call terminate or join on it (although you are allowed to), and you
128	get a coroutine that might have executed other code already (which
129	can be good or bad :).
130
131	On the plus side, this function is faster than creating (and
132	destroying) a completely new coroutine, so if you need a lot of
133	generic coroutines in quick successsion, use "async_pool", not
134	"async".
135
136	The code block is executed in an "eval" context and a warning will
137	be issued in case of an exception instead of terminating the
138	program, as "async" does. As the coroutine is being reused, stuff
139	like "on_destroy" will not work in the expected way, unless you call
140	terminate or cancel, which somehow defeats the purpose of pooling
141	(but is fine in the exceptional case).
142
143	The priority will be reset to 0 after each run, tracing will be
144	disabled, the description will be reset and the default output
145	filehandle gets restored, so you can change all these. Otherwise the
146	coroutine will be re-used "as-is": most notably if you change other
147	per-coroutine global stuff such as $/ you must needs to revert
148	that change, which is most simply done by using local as in: " local
149	$/ ".
150
151	The pool size is limited to 8 idle coroutines (this can be adjusted
152	by changing $Coro::POOL_SIZE), and there can be as many non-idle
153	coros as required.
154
155	If you are concerned about pooled coroutines growing a lot because a
156	single "async_pool" used a lot of stackspace you can e.g.
157	"async_pool { terminate }" once per second or so to slowly replenish
158	the pool. In addition to that, when the stacks used by a handler
159	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also
160	be destroyed.
161
162	STATIC METHODS
163	Static methods are actually functions that operate on the current
164	coroutine.
165
166	schedule
167	Calls the scheduler. The scheduler will find the next coroutine that
168	is to be run from the ready queue and switches to it. The next
169	coroutine to be run is simply the one with the highest priority that
170	is longest in its ready queue. If there is no coroutine ready, it
171	will clal the $Coro::idle hook.
172
173	Please note that the current coroutine will not be put into the
174	ready queue, so calling this function usually means you will never
175	be called again unless something else (e.g. an event handler) calls
176	"->ready", thus waking you up.
177
178	This makes "schedule" the generic method to use to block the
179	current coroutine and wait for events: first you remember the
180	current coroutine in a variable, then arrange for some callback of
181	yours to call "->ready" on that once some event happens, and last
182	you call "schedule" to put yourself to sleep. Note that a lot of
183	things can wake your coroutine up, so you need to check whether the
184	event indeed happened, e.g. by storing the status in a variable.
185
186	The canonical way to wait on external events is this:
187
188	{
189	# remember current coroutine
190	my $current = $Coro::current;
191
192	# register a hypothetical event handler
193	on_event_invoke sub {
194	# wake up sleeping coroutine
195	$current->ready;
196	undef $current;
197	};
198
199	# call schedule until event occurred.
200	# in case we are woken up for other reasons
201	# (current still defined), loop.
202	Coro::schedule while $current;
203	}
204
205	cede
206	"Cede" to other coroutines. This function puts the current coroutine
207	into the ready queue and calls "schedule", which has the effect of
208	giving up the current "timeslice" to other coroutines of the same or
209	higher priority. Once your coroutine gets its turn again it will
210	automatically be resumed.
211
212	This function is often called "yield" in other languages.
213
214	Coro::cede_notself
215	Works like cede, but is not exported by default and will cede to
216	any coroutine, regardless of priority. This is useful sometimes to
217	ensure progress is made.
218
219	terminate [arg...]
220	Terminates the current coroutine with the given status values (see
221	cancel).
222
223	killall
224	Kills/terminates/cancels all coroutines except the currently running
225	one. This is useful after a fork, either in the child or the parent,
226	as usually only one of them should inherit the running coroutines.
227
228	Note that while this will try to free some of the main programs
229	resources, you cannot free all of them, so if a coroutine that is
230	not the main program calls this function, there will be some
231	one-time resource leak.
232
233	COROUTINE METHODS
234	These are the methods you can call on coroutine objects (or to create
235	them).
236
237	new Coro \&sub [, @args...]
238	Create a new coroutine and return it. When the sub returns, the
239	coroutine automatically terminates as if "terminate" with the
240	returned values were called. To make the coroutine run you must
241	first put it into the ready queue by calling the ready method.
242
243	See "async" and "Coro::State::new" for additional info about the
244	coroutine environment.
245
246	$success = $coroutine->ready
247	Put the given coroutine into the end of its ready queue (there is
248	one queue for each priority) and return true. If the coroutine is
249	already in the ready queue, do nothing and return false.
250
251	This ensures that the scheduler will resume this coroutine
252	automatically once all the coroutines of higher priority and all
253	coroutines of the same priority that were put into the ready queue
254	earlier have been resumed.
255
256	$is_ready = $coroutine->is_ready
257	Return whether the coroutine is currently the ready queue or not,
258
259	$coroutine->cancel (arg...)
260	Terminates the given coroutine and makes it return the given
261	arguments as status (default: the empty list). Never returns if the
262	coroutine is the current coroutine.
263
264	$coroutine->join
265	Wait until the coroutine terminates and return any values given to
266	the "terminate" or "cancel" functions. "join" can be called
267	concurrently from multiple coroutines, and all will be resumed and
268	given the status return once the $coroutine terminates.
269
270	$coroutine->on_destroy (\&cb)
271	Registers a callback that is called when this coroutine gets
272	destroyed, but before it is joined. The callback gets passed the
273	terminate arguments, if any, and must not die, under any
274	circumstances.
275
276	$oldprio = $coroutine->prio ($newprio)
277	Sets (or gets, if the argument is missing) the priority of the
278	coroutine. Higher priority coroutines get run before lower priority
279	coroutines. Priorities are small signed integers (currently -4 ..
280	+3), that you can refer to using PRIO_xxx constants (use the import
281	tag :prio to get then):
282
283	PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
284	3 > 1 > 0 > -1 > -3 > -4
285
286	# set priority to HIGH
287	current->prio(PRIO_HIGH);
288
289	The idle coroutine ($Coro::idle) always has a lower priority than
290	any existing coroutine.
291
292	Changing the priority of the current coroutine will take effect
293	immediately, but changing the priority of coroutines in the ready
294	queue (but not running) will only take effect after the next
295	schedule (of that coroutine). This is a bug that will be fixed in
296	some future version.
297
298	$newprio = $coroutine->nice ($change)
299	Similar to "prio", but subtract the given value from the priority
300	(i.e. higher values mean lower priority, just as in unix).
301
302	$olddesc = $coroutine->desc ($newdesc)
303	Sets (or gets in case the argument is missing) the description for
304	this coroutine. This is just a free-form string you can associate
305	with a coroutine.
306
307	This method simply sets the "$coroutine->{desc}" member to the given
308	string. You can modify this member directly if you wish.
309
310	$coroutine->throw ([$scalar])
311	If $throw is specified and defined, it will be thrown as an
312	exception inside the coroutine at the next convinient point in time
313	(usually after it gains control at the next schedule/transfer/cede).
314	Otherwise clears the exception object.
315
316	The exception object will be thrown "as is" with the specified
317	scalar in $@, i.e. if it is a string, no line number or newline will
318	be appended (unlike with "die").
319
320	This can be used as a softer means than "cancel" to ask a coroutine
321	to end itself, although there is no guarentee that the exception
322	will lead to termination, and if the exception isn't caught it might
323	well end the whole program.
324
325	GLOBAL FUNCTIONS
326	Coro::nready
327	Returns the number of coroutines that are currently in the ready
328	state, i.e. that can be switched to by calling "schedule" directory
329	or indirectly. The value 0 means that the only runnable coroutine is
330	the currently running one, so "cede" would have no effect, and
331	"schedule" would cause a deadlock unless there is an idle handler
332	that wakes up some coroutines.
333
334	my $guard = Coro::guard { ... }
335	This creates and returns a guard object. Nothing happens until the
336	object gets destroyed, in which case the codeblock given as argument
337	will be executed. This is useful to free locks or other resources in
338	case of a runtime error or when the coroutine gets canceled, as in
339	both cases the guard block will be executed. The guard object
340	supports only one method, "->cancel", which will keep the codeblock
341	from being executed.
342
343	Example: set some flag and clear it again when the coroutine gets
344	canceled or the function returns:
345
346	sub do_something {
347	my $guard = Coro::guard { $busy = 0 };
348	$busy = 1;
349
350	# do something that requires $busy to be true
351	}
352
353	unblock_sub { ... }
354	This utility function takes a BLOCK or code reference and "unblocks"
355	it, returning a new coderef. Unblocking means that calling the new
356	coderef will return immediately without blocking, returning nothing,
357	while the original code ref will be called (with parameters) from
358	within another coroutine.
359
360	The reason this function exists is that many event libraries (such
361	as the venerable Event module) are not coroutine-safe (a weaker form
362	of thread-safety). This means you must not block within event
363	callbacks, otherwise you might suffer from crashes or worse. The
364	only event library currently known that is safe to use without
365	"unblock_sub" is EV.
366
367	This function allows your callbacks to block by executing them in
368	another coroutine where it is safe to block. One example where
369	blocking is handy is when you use the Coro::AIO functions to save
370	results to disk, for example.
371
372	In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
373	when creating event callbacks that want to block.
374
375	If your handler does not plan to block (e.g. simply sends a message
376	to another coroutine, or puts some other coroutine into the ready
377	queue), there is no reason to use "unblock_sub".
378
379	Note that you also need to use "unblock_sub" for any other callbacks
380	that are indirectly executed by any C-based event loop. For example,
381	when you use a module that uses AnyEvent (and you use
382	Coro::AnyEvent) and it provides callbacks that are the result of
383	some event callback, then you must not block either, or use
384	"unblock_sub".
385
386	BUGS/LIMITATIONS
387	This module is not perl-pseudo-thread-safe. You should only ever use
388	this module from the same thread (this requirement might be removed in
389	the future to allow per-thread schedulers, but Coro::State does not yet
390	allow this). I recommend disabling thread support and using processes,
391	as this is much faster and uses less memory.
392
393	SEE ALSO
394	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
395
396	Debugging: Coro::Debug.
397
398	Support/Utility: Coro::Specific, Coro::Util.
399
400	Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
401	Coro::SemaphoreSet, Coro::RWLock.
402
403	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
404
405	Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
406
407	XS API: Coro::MakeMaker.
408
409	Low level Configuration, Coroutine Environment: Coro::State.
410
411	AUTHOR
412	Marc Lehmann <schmorp@schmorp.de>
413	http://home.schmorp.de/
414