[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
      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 wether 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 wether 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 cnanot 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 wether the coroutine is currently the ready queue or not,

    $coroutine->cancel (arg...)
        Terminates the given coroutine and makes it return the given
        arguments as status (default: the empty list). Never returns if the
        coroutine is the current coroutine.

    $coroutine->join
        Wait until the coroutine terminates and return any values given to
        the "terminate" or "cancel" functions. "join" can be called
        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:	1.14
Committed:	Sat May 10 22:32:40 2008 UTC (16 years ago) by root
Branch:	MAIN
CVS Tags:	rel-4_741, rel-4_743, rel-4_742, rel-4_744, rel-4_74, rel-4_71, rel-4_72, rel-4_73, rel-4_745, rel-4_7
Changes since 1.13:	+192 -105 lines
Log Message:	* empty log message *
#	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			my $lock = new Coro::Semaphore;
20			my $locked;
21
22			$lock->down;
23			$locked = 1;
24			$lock->up;
25	root	1.1
26			DESCRIPTION
27			This module collection manages coroutines. Coroutines are similar to
28	root	1.14	threads but don't (in general) run in parallel at the same time even on
29			SMP machines. The specific flavor of coroutine used in this module also
30			guarantees you that it will not switch between coroutines unless
31			necessary, at easily-identified points in your program, so locking and
32			parallel access are rarely an issue, making coroutine programming much
33			safer and easier than threads programming.
34
35			Unlike a normal perl program, however, coroutines allow you to have
36			multiple running interpreters that share data, which is especially
37			useful to code pseudo-parallel processes and for event-based
38			programming, such as multiple HTTP-GET requests running concurrently.
39			See Coro::AnyEvent to learn more.
40
41			Coroutines are also useful because Perl has no support for threads (the
42			so called "threads" that perl offers are nothing more than the (bad)
43			process emulation coming from the Windows platform: On standard
44			operating systems they serve no purpose whatsoever, except by making
45			your programs slow and making them use a lot of memory. Best disable
46			them when building perl, or aks your software vendor/distributor to do
47			it for you).
48	root	1.1
49			In this module, coroutines are defined as "callchain + lexical variables
50	root	1.5	+ @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
51			callchain, its own set of lexicals and its own set of perls most
52	root	1.12	important global variables (see Coro::State for more configuration).
53	root	1.1
54	root	1.14	$Coro::main
55			This variable stores the coroutine object that represents the main
56			program. While you cna "ready" it and do most other things you can
57			do to coroutines, it is mainly useful to compare again
58			$Coro::current, to see wether you are running in the main program or
59			not.
60
61			$Coro::current
62			The coroutine object representing the current coroutine (the last
63			coroutine that the Coro scheduler switched to). The initial value is
64			$main (of course).
65
66			This variable is strictly read-only. You can take copies of the
67			value stored in it and use it as any other coroutine object, but you
68			must not otherwise modify the variable itself.
69
70			$Coro::idle
71			This variable is mainly useful to integrate Coro into event loops.
72			It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as
73			this is pretty low-level functionality.
74
75			This variable stores a callback that is called whenever the
76			scheduler finds no ready coroutines to run. The default
77			implementation prints "FATAL: deadlock detected" and exits, because
78			the program has no other way to continue.
79
80			This hook is overwritten by modules such as "Coro::Timer" and
81			"Coro::AnyEvent" to wait on an external event that hopefully wake up
82			a coroutine so the scheduler can run it.
83	root	1.1
84	root	1.14	Note that the callback must not, under any circumstances, block
85			the current coroutine. Normally, this is achieved by having an "idle
86			coroutine" that calls the event loop and then blocks again, and then
87			readying that coroutine in the idle handler.
88	root	1.4
89	root	1.14	See Coro::Event or Coro::AnyEvent for examples of using this
90			technique.
91	root	1.4
92			Please note that if your callback recursively invokes perl (e.g. for
93	root	1.12	event handlers), then it must be prepared to be called recursively
94			itself.
95	root	1.1
96	root	1.14	SIMPLE COROUTINE CREATION
97			async { ... } [@args...]
98			Create a new coroutine and return it's coroutine object (usually
99			unused). The coroutine will be put into the ready queue, so it will
100			start running automatically on the next scheduler run.
101	root	1.1
102	root	1.14	The first argument is a codeblock/closure that should be executed in
103			the coroutine. When it returns argument returns the coroutine is
104	root	1.1	automatically terminated.
105
106	root	1.14	The remaining arguments are passed as arguments to the closure.
107
108	root	1.10	See the "Coro::State::new" constructor for info about the coroutine
109	root	1.14	environment in which coroutines are executed.
110	root	1.10
111	root	1.7	Calling "exit" in a coroutine will do the same as calling exit
112			outside the coroutine. Likewise, when the coroutine dies, the
113			program will exit, just as it would in the main program.
114	root	1.3
115	root	1.14	If you do not want that, you can provide a default "die" handler, or
116			simply avoid dieing (by use of "eval").
117
118			Example: Create a new coroutine that just prints its arguments.
119
120	root	1.1	async {
121			print "@_\n";
122			} 1,2,3,4;
123
124	root	1.6	async_pool { ... } [@args...]
125			Similar to "async", but uses a coroutine pool, so you should not
126	root	1.14	call terminate or join on it (although you are allowed to), and you
127			get a coroutine that might have executed other code already (which
128			can be good or bad :).
129
130			On the plus side, this function is faster than creating (and
131			destroying) a completely new coroutine, so if you need a lot of
132			generic coroutines in quick successsion, use "async_pool", not
133			"async".
134	root	1.6
135	root	1.14	The code block is executed in an "eval" context and a warning will
136	root	1.6	be issued in case of an exception instead of terminating the
137			program, as "async" does. As the coroutine is being reused, stuff
138			like "on_destroy" will not work in the expected way, unless you call
139	root	1.14	terminate or cancel, which somehow defeats the purpose of pooling
140			(but is fine in the exceptional case).
141	root	1.6
142	root	1.14	The priority will be reset to 0 after each run, tracing will be
143	root	1.10	disabled, the description will be reset and the default output
144	root	1.14	filehandle gets restored, so you can change all these. Otherwise the
145			coroutine will be re-used "as-is": most notably if you change other
146			per-coroutine global stuff such as $/ you must needs to revert
147			that change, which is most simply done by using local as in: " local
148			$/ ".
149	root	1.6
150			The pool size is limited to 8 idle coroutines (this can be adjusted
151			by changing $Coro::POOL_SIZE), and there can be as many non-idle
152			coros as required.
153
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			things can wake your coroutine up, so you need to check wether the
183			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			resources, you cnanot free all of them, so if a coroutine that is
229			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			Return wether the coroutine is currently the ready queue or not,
257
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	1.4	$coroutine->join
264	root	1.1	Wait until the coroutine terminates and return any values given to
265	root	1.10	the "terminate" or "cancel" functions. "join" can be called
266	root	1.14	concurrently from multiple coroutines, and all will be resumed and
267			given the status return once the $coroutine terminates.
268	root	1.1
269	root	1.6	$coroutine->on_destroy (\&cb)
270			Registers a callback that is called when this coroutine gets
271			destroyed, but before it is joined. The callback gets passed the
272	root	1.14	terminate arguments, if any, and must not die, under any
273			circumstances.
274	root	1.6
275	root	1.4	$oldprio = $coroutine->prio ($newprio)
276	root	1.1	Sets (or gets, if the argument is missing) the priority of the
277	root	1.4	coroutine. Higher priority coroutines get run before lower priority
278			coroutines. Priorities are small signed integers (currently -4 ..
279	root	1.1	+3), that you can refer to using PRIO_xxx constants (use the import
280			tag :prio to get then):
281
282			PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
283			3 > 1 > 0 > -1 > -3 > -4
284
285			# set priority to HIGH
286			current->prio(PRIO_HIGH);
287
288			The idle coroutine ($Coro::idle) always has a lower priority than
289			any existing coroutine.
290
291	root	1.4	Changing the priority of the current coroutine will take effect
292			immediately, but changing the priority of coroutines in the ready
293	root	1.1	queue (but not running) will only take effect after the next
294	root	1.4	schedule (of that coroutine). This is a bug that will be fixed in
295			some future version.
296	root	1.1
297	root	1.4	$newprio = $coroutine->nice ($change)
298	root	1.1	Similar to "prio", but subtract the given value from the priority
299			(i.e. higher values mean lower priority, just as in unix).
300
301	root	1.4	$olddesc = $coroutine->desc ($newdesc)
302	root	1.1	Sets (or gets in case the argument is missing) the description for
303	root	1.4	this coroutine. This is just a free-form string you can associate
304			with a coroutine.
305
306	root	1.10	This method simply sets the "$coroutine->{desc}" member to the given
307			string. You can modify this member directly if you wish.
308
309	root	1.11	$coroutine->throw ([$scalar])
310			If $throw is specified and defined, it will be thrown as an
311			exception inside the coroutine at the next convinient point in time
312			(usually after it gains control at the next schedule/transfer/cede).
313			Otherwise clears the exception object.
314
315			The exception object will be thrown "as is" with the specified
316			scalar in $@, i.e. if it is a string, no line number or newline will
317			be appended (unlike with "die").
318
319			This can be used as a softer means than "cancel" to ask a coroutine
320			to end itself, although there is no guarentee that the exception
321			will lead to termination, and if the exception isn't caught it might
322			well end the whole program.
323
324	root	1.5	GLOBAL FUNCTIONS
325			Coro::nready
326			Returns the number of coroutines that are currently in the ready
327	root	1.14	state, i.e. that can be switched to by calling "schedule" directory
328			or indirectly. The value 0 means that the only runnable coroutine is
329			the currently running one, so "cede" would have no effect, and
330			"schedule" would cause a deadlock unless there is an idle handler
331			that wakes up some coroutines.
332	root	1.5
333	root	1.6	my $guard = Coro::guard { ... }
334			This creates and returns a guard object. Nothing happens until the
335	root	1.7	object gets destroyed, in which case the codeblock given as argument
336	root	1.6	will be executed. This is useful to free locks or other resources in
337			case of a runtime error or when the coroutine gets canceled, as in
338			both cases the guard block will be executed. The guard object
339			supports only one method, "->cancel", which will keep the codeblock
340			from being executed.
341
342			Example: set some flag and clear it again when the coroutine gets
343			canceled or the function returns:
344
345			sub do_something {
346			my $guard = Coro::guard { $busy = 0 };
347			$busy = 1;
348
349			# do something that requires $busy to be true
350			}
351
352	root	1.4	unblock_sub { ... }
353			This utility function takes a BLOCK or code reference and "unblocks"
354	root	1.14	it, returning a new coderef. Unblocking means that calling the new
355			coderef will return immediately without blocking, returning nothing,
356			while the original code ref will be called (with parameters) from
357			within another coroutine.
358	root	1.4
359	root	1.8	The reason this function exists is that many event libraries (such
360	root	1.4	as the venerable Event module) are not coroutine-safe (a weaker form
361			of thread-safety). This means you must not block within event
362	root	1.14	callbacks, otherwise you might suffer from crashes or worse. The
363			only event library currently known that is safe to use without
364			"unblock_sub" is EV.
365	root	1.4
366			This function allows your callbacks to block by executing them in
367			another coroutine where it is safe to block. One example where
368			blocking is handy is when you use the Coro::AIO functions to save
369	root	1.14	results to disk, for example.
370	root	1.4
371			In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
372			when creating event callbacks that want to block.
373	root	1.1
374	root	1.14	If your handler does not plan to block (e.g. simply sends a message
375			to another coroutine, or puts some other coroutine into the ready
376			queue), there is no reason to use "unblock_sub".
377
378			Note that you also need to use "unblock_sub" for any other callbacks
379			that are indirectly executed by any C-based event loop. For example,
380			when you use a module that uses AnyEvent (and you use
381			Coro::AnyEvent) and it provides callbacks that are the result of
382			some event callback, then you must not block either, or use
383			"unblock_sub".
384
385	root	1.1	BUGS/LIMITATIONS
386	root	1.14	This module is not perl-pseudo-thread-safe. You should only ever use
387			this module from the same thread (this requirement might be removed in
388			the future to allow per-thread schedulers, but Coro::State does not yet
389			allow this). I recommend disabling thread support and using processes,
390			as this is much faster and uses less memory.
391	root	1.1
392			SEE ALSO
393	root	1.14	Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
394	root	1.12
395			Debugging: Coro::Debug.
396
397			Support/Utility: Coro::Specific, Coro::Util.
398	root	1.2
399			Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
400			Coro::SemaphoreSet, Coro::RWLock.
401
402	root	1.14	IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
403
404			Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
405	root	1.12
406	root	1.14	XS API: Coro::MakeMaker.
407	root	1.2
408	root	1.14	Low level Configuration, Coroutine Environment: Coro::State.
409	root	1.1
410			AUTHOR
411			Marc Lehmann <schmorp@schmorp.de>
412			http://home.schmorp.de/
413