[ViewVC] Annotation 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 completly 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* revert that
        change, which is most simply done by using local as in: "local $/".

        The idle pool size is limited to 8 idle coroutines (this can be
        adjusted by changing $Coro::POOL_SIZE), but 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.

    $coroutine->throw ([$scalar])
        If $throw is specified and defined, it will be thrown as an
        exception inside the coroutine at the next convenient 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 guarantee that the exception
        will lead to termination, and if the exception isn't caught it might
        well end the whole program.

        You might also think of "throw" as being the moral equivalent of
        "kill"ing a coroutine with a signal (in this case, a scalar).

    $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.

  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:	1.17
Committed:	Wed Nov 5 15:38:10 2008 UTC (15 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-4_91, rel-4_9, rel-4_804, rel-4_901, rel-4_911, rel-4_912
Changes since 1.16:	+18 -15 lines
Log Message:	4.804
#	User	Rev	Content
1	root	1.1	NAME
2			Coro - coroutine process abstraction
3
4			SYNOPSIS
5	root	1.14	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	root	1.15	use Coro::Semaphore;
20	root	1.14	my $lock = new Coro::Semaphore;
21			my $locked;
22
23			$lock->down;
24			$locked = 1;
25			$lock->up;
26	root	1.1
27			DESCRIPTION
28			This module collection manages coroutines. Coroutines are similar to
29	root	1.14	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	root	1.1
50			In this module, coroutines are defined as "callchain + lexical variables
51	root	1.5	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
52			callchain, its own set of lexicals and its own set of perls most
53	root	1.12	important global variables (see Coro::State for more configuration).
54	root	1.1
55	root	1.14	$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	root	1.15	$Coro::current, to see whether you are running in the main program
60			or not.
61	root	1.14
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	root	1.1
85	root	1.14	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	root	1.4
90	root	1.14	See Coro::Event or Coro::AnyEvent for examples of using this
91			technique.
92	root	1.4
93			Please note that if your callback recursively invokes perl (e.g. for
94	root	1.12	event handlers), then it must be prepared to be called recursively
95			itself.
96	root	1.1
97	root	1.14	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	root	1.1
103	root	1.14	The first argument is a codeblock/closure that should be executed in
104			the coroutine. When it returns argument returns the coroutine is
105	root	1.1	automatically terminated.
106
107	root	1.14	The remaining arguments are passed as arguments to the closure.
108
109	root	1.10	See the "Coro::State::new" constructor for info about the coroutine
110	root	1.14	environment in which coroutines are executed.
111	root	1.10
112	root	1.7	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	root	1.3
116	root	1.14	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	root	1.1	async {
122			print "@_\n";
123			} 1,2,3,4;
124
125	root	1.6	async_pool { ... } [@args...]
126			Similar to "async", but uses a coroutine pool, so you should not
127	root	1.14	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	root	1.16	destroying) a completly new coroutine, so if you need a lot of
133	root	1.14	generic coroutines in quick successsion, use "async_pool", not
134			"async".
135	root	1.6
136	root	1.14	The code block is executed in an "eval" context and a warning will
137	root	1.6	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	root	1.14	terminate or cancel, which somehow defeats the purpose of pooling
141			(but is fine in the exceptional case).
142	root	1.6
143	root	1.14	The priority will be reset to 0 after each run, tracing will be
144	root	1.10	disabled, the description will be reset and the default output
145	root	1.14	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	root	1.16	per-coroutine global stuff such as $/ you must needs revert that
148			change, which is most simply done by using local as in: "local $/".
149
150			The idle pool size is limited to 8 idle coroutines (this can be
151			adjusted by changing $Coro::POOL_SIZE), but there can be as many
152			non-idle coros as required.
153	root	1.6
154			If you are concerned about pooled coroutines growing a lot because a
155			single "async_pool" used a lot of stackspace you can e.g.
156			"async_pool { terminate }" once per second or so to slowly replenish
157	root	1.9	the pool. In addition to that, when the stacks used by a handler
158	root	1.14	grows larger than 16kb (adjustable via $Coro::POOL_RSS) it will also
159			be destroyed.
160
161			STATIC METHODS
162			Static methods are actually functions that operate on the current
163			coroutine.
164	root	1.6
165	root	1.1	schedule
166	root	1.14	Calls the scheduler. The scheduler will find the next coroutine that
167			is to be run from the ready queue and switches to it. The next
168			coroutine to be run is simply the one with the highest priority that
169			is longest in its ready queue. If there is no coroutine ready, it
170			will clal the $Coro::idle hook.
171
172			Please note that the current coroutine will not be put into the
173			ready queue, so calling this function usually means you will never
174			be called again unless something else (e.g. an event handler) calls
175			"->ready", thus waking you up.
176
177			This makes "schedule" the generic method to use to block the
178			current coroutine and wait for events: first you remember the
179			current coroutine in a variable, then arrange for some callback of
180			yours to call "->ready" on that once some event happens, and last
181			you call "schedule" to put yourself to sleep. Note that a lot of
182	root	1.15	things can wake your coroutine up, so you need to check whether the
183	root	1.14	event indeed happened, e.g. by storing the status in a variable.
184	root	1.4
185			The canonical way to wait on external events is this:
186
187			{
188			# remember current coroutine
189			my $current = $Coro::current;
190
191			# register a hypothetical event handler
192			on_event_invoke sub {
193			# wake up sleeping coroutine
194			$current->ready;
195			undef $current;
196			};
197
198	root	1.8	# call schedule until event occurred.
199	root	1.4	# in case we are woken up for other reasons
200			# (current still defined), loop.
201			Coro::schedule while $current;
202			}
203	root	1.1
204			cede
205	root	1.4	"Cede" to other coroutines. This function puts the current coroutine
206	root	1.1	into the ready queue and calls "schedule", which has the effect of
207			giving up the current "timeslice" to other coroutines of the same or
208	root	1.14	higher priority. Once your coroutine gets its turn again it will
209			automatically be resumed.
210
211			This function is often called "yield" in other languages.
212	root	1.1
213	root	1.6	Coro::cede_notself
214	root	1.14	Works like cede, but is not exported by default and will cede to
215			any coroutine, regardless of priority. This is useful sometimes to
216			ensure progress is made.
217	root	1.6
218	root	1.1	terminate [arg...]
219	root	1.4	Terminates the current coroutine with the given status values (see
220	root	1.1	cancel).
221
222	root	1.10	killall
223			Kills/terminates/cancels all coroutines except the currently running
224			one. This is useful after a fork, either in the child or the parent,
225			as usually only one of them should inherit the running coroutines.
226
227	root	1.14	Note that while this will try to free some of the main programs
228	root	1.15	resources, you cannot free all of them, so if a coroutine that is
229	root	1.14	not the main program calls this function, there will be some
230			one-time resource leak.
231	root	1.1
232	root	1.4	COROUTINE METHODS
233	root	1.14	These are the methods you can call on coroutine objects (or to create
234			them).
235	root	1.1
236			new Coro \&sub [, @args...]
237	root	1.14	Create a new coroutine and return it. When the sub returns, the
238	root	1.4	coroutine automatically terminates as if "terminate" with the
239			returned values were called. To make the coroutine run you must
240			first put it into the ready queue by calling the ready method.
241
242	root	1.10	See "async" and "Coro::State::new" for additional info about the
243			coroutine environment.
244	root	1.4
245			$success = $coroutine->ready
246	root	1.14	Put the given coroutine into the end of its ready queue (there is
247			one queue for each priority) and return true. If the coroutine is
248			already in the ready queue, do nothing and return false.
249
250			This ensures that the scheduler will resume this coroutine
251			automatically once all the coroutines of higher priority and all
252			coroutines of the same priority that were put into the ready queue
253			earlier have been resumed.
254	root	1.4
255			$is_ready = $coroutine->is_ready
256	root	1.15	Return whether the coroutine is currently the ready queue or not,
257	root	1.4
258			$coroutine->cancel (arg...)
259			Terminates the given coroutine and makes it return the given
260	root	1.6	arguments as status (default: the empty list). Never returns if the
261			coroutine is the current coroutine.
262	root	1.1
263	root	1.17	$coroutine->throw ([$scalar])
264			If $throw is specified and defined, it will be thrown as an
265			exception inside the coroutine at the next convenient point in time
266			(usually after it gains control at the next schedule/transfer/cede).
267			Otherwise clears the exception object.
268
269			The exception object will be thrown "as is" with the specified
270			scalar in $@, i.e. if it is a string, no line number or newline will
271			be appended (unlike with "die").
272
273			This can be used as a softer means than "cancel" to ask a coroutine
274			to end itself, although there is no guarantee that the exception
275			will lead to termination, and if the exception isn't caught it might
276			well end the whole program.
277
278			You might also think of "throw" as being the moral equivalent of
279			"kill"ing a coroutine with a signal (in this case, a scalar).
280
281	root	1.4	$coroutine->join
282	root	1.1	Wait until the coroutine terminates and return any values given to
283	root	1.10	the "terminate" or "cancel" functions. "join" can be called
284	root	1.14	concurrently from multiple coroutines, and all will be resumed and
285			given the status return once the $coroutine terminates.
286	root	1.1
287	root	1.6	$coroutine->on_destroy (\&cb)
288			Registers a callback that is called when this coroutine gets
289			destroyed, but before it is joined. The callback gets passed the
290	root	1.14	terminate arguments, if any, and must not die, under any
291			circumstances.
292	root	1.6
293	root	1.4	$oldprio = $coroutine->prio ($newprio)
294	root	1.1	Sets (or gets, if the argument is missing) the priority of the
295	root	1.4	coroutine. Higher priority coroutines get run before lower priority
296			coroutines. Priorities are small signed integers (currently -4 ..
297	root	1.1	+3), that you can refer to using PRIO_xxx constants (use the import
298			tag :prio to get then):
299
300			PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
301			3 > 1 > 0 > -1 > -3 > -4
302
303			# set priority to HIGH
304			current->prio(PRIO_HIGH);
305
306			The idle coroutine ($Coro::idle) always has a lower priority than
307			any existing coroutine.
308
309	root	1.4	Changing the priority of the current coroutine will take effect
310			immediately, but changing the priority of coroutines in the ready
311	root	1.1	queue (but not running) will only take effect after the next
312	root	1.4	schedule (of that coroutine). This is a bug that will be fixed in
313			some future version.
314	root	1.1
315	root	1.4	$newprio = $coroutine->nice ($change)
316	root	1.1	Similar to "prio", but subtract the given value from the priority
317			(i.e. higher values mean lower priority, just as in unix).
318
319	root	1.4	$olddesc = $coroutine->desc ($newdesc)
320	root	1.1	Sets (or gets in case the argument is missing) the description for
321	root	1.4	this coroutine. This is just a free-form string you can associate
322			with a coroutine.
323
324	root	1.10	This method simply sets the "$coroutine->{desc}" member to the given
325			string. You can modify this member directly if you wish.
326
327	root	1.5	GLOBAL FUNCTIONS
328			Coro::nready
329			Returns the number of coroutines that are currently in the ready
330	root	1.14	state, i.e. that can be switched to by calling "schedule" directory
331			or indirectly. The value 0 means that the only runnable coroutine is
332			the currently running one, so "cede" would have no effect, and
333			"schedule" would cause a deadlock unless there is an idle handler
334			that wakes up some coroutines.
335	root	1.5
336	root	1.6	my $guard = Coro::guard { ... }
337			This creates and returns a guard object. Nothing happens until the
338	root	1.7	object gets destroyed, in which case the codeblock given as argument
339	root	1.6	will be executed. This is useful to free locks or other resources in
340			case of a runtime error or when the coroutine gets canceled, as in
341			both cases the guard block will be executed. The guard object
342			supports only one method, "->cancel", which will keep the codeblock
343			from being executed.
344
345			Example: set some flag and clear it again when the coroutine gets
346			canceled or the function returns:
347
348			sub do_something {
349			my $guard = Coro::guard { $busy = 0 };
350			$busy = 1;
351
352			# do something that requires $busy to be true
353			}
354
355	root	1.4	unblock_sub { ... }
356			This utility function takes a BLOCK or code reference and "unblocks"
357	root	1.14	it, returning a new coderef. Unblocking means that calling the new
358			coderef will return immediately without blocking, returning nothing,
359			while the original code ref will be called (with parameters) from
360			within another coroutine.
361	root	1.4
362	root	1.8	The reason this function exists is that many event libraries (such
363	root	1.4	as the venerable Event module) are not coroutine-safe (a weaker form
364			of thread-safety). This means you must not block within event
365	root	1.14	callbacks, otherwise you might suffer from crashes or worse. The
366			only event library currently known that is safe to use without
367			"unblock_sub" is EV.
368	root	1.4
369			This function allows your callbacks to block by executing them in
370			another coroutine where it is safe to block. One example where
371			blocking is handy is when you use the Coro::AIO functions to save
372	root	1.14	results to disk, for example.
373	root	1.4
374			In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
375			when creating event callbacks that want to block.
376	root	1.1
377	root	1.14	If your handler does not plan to block (e.g. simply sends a message
378			to another coroutine, or puts some other coroutine into the ready
379			queue), there is no reason to use "unblock_sub".
380
381			Note that you also need to use "unblock_sub" for any other callbacks
382			that are indirectly executed by any C-based event loop. For example,
383			when you use a module that uses AnyEvent (and you use
384			Coro::AnyEvent) and it provides callbacks that are the result of
385			some event callback, then you must not block either, or use
386			"unblock_sub".
387
388	root	1.1	BUGS/LIMITATIONS
389	root	1.14	This module is not perl-pseudo-thread-safe. You should only ever use
390			this module from the same thread (this requirement might be removed in
391			the future to allow per-thread schedulers, but Coro::State does not yet
392			allow this). I recommend disabling thread support and using processes,
393			as this is much faster and uses less memory.
394	root	1.1
395			SEE ALSO
396	root	1.14	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
397	root	1.12
398			Debugging: Coro::Debug.
399
400			Support/Utility: Coro::Specific, Coro::Util.
401	root	1.2
402			Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
403			Coro::SemaphoreSet, Coro::RWLock.
404
405	root	1.14	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
406
407			Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
408	root	1.12
409	root	1.14	XS API: Coro::MakeMaker.
410	root	1.2
411	root	1.14	Low level Configuration, Coroutine Environment: Coro::State.
412	root	1.1
413			AUTHOR
414			Marc Lehmann <schmorp@schmorp.de>
415			http://home.schmorp.de/
416