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1NAME 1NAME
2 Coro - coroutine process abstraction 2 Coro - coroutine process abstraction
3 3
4SYNOPSIS 4SYNOPSIS
5 use Coro; 5 use Coro;
6 6
7 async { 7 async {
8 # some asynchronous thread of execution 8 # some asynchronous thread of execution
9 print "2\n";
10 cede; # yield back to main
11 print "4\n";
9 }; 12 };
10 13 print "1\n";
11 # alternatively create an async process like this: 14 cede; # yield to coroutine
12 15 print "3\n";
13 sub some_func : Coro { 16 cede; # and again
14 # some more async code
15 } 17
16 18 # use locking
17 cede; 19 use Coro::Semaphore;
20 my $lock = new Coro::Semaphore;
21 my $locked;
22
23 $lock->down;
24 $locked = 1;
25 $lock->up;
18 26
19DESCRIPTION 27DESCRIPTION
20 This module collection manages coroutines. Coroutines are similar to 28 This module collection manages coroutines. Coroutines are similar to
21 threads but don't run in parallel. 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).
22 49
23 In this module, coroutines are defined as "callchain + lexical variables 50 In this module, coroutines are defined as "callchain + lexical variables
24 + @_ + $_ + $@ + $^W + C stack), that is, a coroutine has it's own 51 + @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
25 callchain, it's own set of lexicals and it's own set of perl's most 52 callchain, its own set of lexicals and its own set of perls most
26 important global variables. 53 important global variables (see Coro::State for more configuration).
27 54
28 $main 55 $Coro::main
29 This coroutine represents the main program. 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.
30 61
31 $current (or as function: current) 62 $Coro::current
32 The current coroutine (the last coroutine switched to). The initial 63 The coroutine object representing the current coroutine (the last
64 coroutine that the Coro scheduler switched to). The initial value is
33 value is $main (of course). 65 $Coro::main (of course).
34 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
35 $idle 71 $Coro::idle
36 The coroutine to switch to when no other coroutine is running. The 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
37 default implementation prints "FATAL: deadlock detected" and exits. 78 implementation prints "FATAL: deadlock detected" and exits, because
79 the program has no other way to continue.
38 80
39 STATIC METHODS 81 This hook is overwritten by modules such as "Coro::Timer" and
40 Static methods are actually functions that operate on the current 82 "Coro::AnyEvent" to wait on an external event that hopefully wake up
41 process only. 83 a coroutine so the scheduler can run it.
42 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
43 async { ... } [@args...] 98 async { ... } [@args...]
44 Create a new asynchronous process and return it's process object 99 Create a new coroutine and return it's coroutine object (usually
45 (usually unused). When the sub returns the new process is 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
46 automatically terminated. 105 automatically terminated.
47 106
48 When the coroutine dies, the program will exit, just as in the main 107 The remaining arguments are passed as arguments to the closure.
49 program.
50 108
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
51 # create a new coroutine that just prints its arguments 119 Example: Create a new coroutine that just prints its arguments.
120
52 async { 121 async {
53 print "@_\n"; 122 print "@_\n";
54 } 1,2,3,4; 123 } 1,2,3,4;
55 124
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 about twice as fast as creating
132 (and 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* 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
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 the pool. In addition to that, when the stacks used by a handler
158 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
56 schedule 165 schedule
57 Calls the scheduler. Please note that the current process will not 166 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
58 be put into the ready queue, so calling this function usually means 173 ready queue, so calling this function usually means you will never
59 you will never be called again. 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 whether the
183 event indeed happened, e.g. by storing the status in a variable.
184
185 See HOW TO WAIT FOR A CALLBACK, below, for some ways to wait for
186 callbacks.
60 187
61 cede 188 cede
62 "Cede" to other processes. This function puts the current process 189 "Cede" to other coroutines. This function puts the current coroutine
63 into the ready queue and calls "schedule", which has the effect of 190 into the ready queue and calls "schedule", which has the effect of
64 giving up the current "timeslice" to other coroutines of the same or 191 giving up the current "timeslice" to other coroutines of the same or
65 higher priority. 192 higher priority. Once your coroutine gets its turn again it will
193 automatically be resumed.
194
195 This function is often called "yield" in other languages.
196
197 Coro::cede_notself
198 Works like cede, but is not exported by default and will cede to
199 *any* coroutine, regardless of priority. This is useful sometimes to
200 ensure progress is made.
66 201
67 terminate [arg...] 202 terminate [arg...]
68 Terminates the current process with the given status values (see 203 Terminates the current coroutine with the given status values (see
69 cancel). 204 cancel).
70 205
71 # dynamic methods 206 killall
207 Kills/terminates/cancels all coroutines except the currently running
208 one. This is useful after a fork, either in the child or the parent,
209 as usually only one of them should inherit the running coroutines.
72 210
73 PROCESS METHODS 211 Note that while this will try to free some of the main programs
212 resources, you cannot free all of them, so if a coroutine that is
213 not the main program calls this function, there will be some
214 one-time resource leak.
215
216 COROUTINE METHODS
74 These are the methods you can call on process objects. 217 These are the methods you can call on coroutine objects (or to create
218 them).
75 219
76 new Coro \&sub [, @args...] 220 new Coro \&sub [, @args...]
77 Create a new process and return it. When the sub returns the process 221 Create a new coroutine and return it. When the sub returns, the
78 automatically terminates as if "terminate" with the returned values 222 coroutine automatically terminates as if "terminate" with the
79 were called. To make the process run you must first put it into the 223 returned values were called. To make the coroutine run you must
80 ready queue by calling the ready method. 224 first put it into the ready queue by calling the ready method.
81 225
82 $process->ready 226 See "async" and "Coro::State::new" for additional info about the
83 Put the given process into the ready queue. 227 coroutine environment.
84 228
229 $success = $coroutine->ready
230 Put the given coroutine into the end of its ready queue (there is
231 one queue for each priority) and return true. If the coroutine is
232 already in the ready queue, do nothing and return false.
233
234 This ensures that the scheduler will resume this coroutine
235 automatically once all the coroutines of higher priority and all
236 coroutines of the same priority that were put into the ready queue
237 earlier have been resumed.
238
239 $is_ready = $coroutine->is_ready
240 Return whether the coroutine is currently the ready queue or not,
241
85 $process->cancel (arg...) 242 $coroutine->cancel (arg...)
86 Terminates the given process and makes it return the given arguments 243 Terminates the given coroutine and makes it return the given
87 as status (default: the empty list). 244 arguments as status (default: the empty list). Never returns if the
245 coroutine is the current coroutine.
88 246
89 $process->join 247 $coroutine->schedule_to
248 Puts the current coroutine to sleep (like "Coro::schedule"), but
249 instead of continuing with the next coro from the ready queue,
250 always switch to the given coroutine object (regardless of priority
251 etc.). The readyness state of that coroutine isn't changed.
252
253 This is an advanced method for special cases - I'd love to hear
254 about any uses for this one.
255
256 $coroutine->cede_to
257 Like "schedule_to", but puts the current coroutine into the ready
258 queue. This has the effect of temporarily switching to the given
259 coroutine, and continuing some time later.
260
261 This is an advanced method for special cases - I'd love to hear
262 about any uses for this one.
263
264 $coroutine->throw ([$scalar])
265 If $throw is specified and defined, it will be thrown as an
266 exception inside the coroutine at the next convenient point in time.
267 Otherwise clears the exception object.
268
269 Coro will check for the exception each time a schedule-like-function
270 returns, i.e. after each "schedule", "cede",
271 "Coro::Semaphore->down", "Coro::Handle->readable" and so on. Most of
272 these functions detect this case and return early in case an
273 exception is pending.
274
275 The exception object will be thrown "as is" with the specified
276 scalar in $@, i.e. if it is a string, no line number or newline will
277 be appended (unlike with "die").
278
279 This can be used as a softer means than "cancel" to ask a coroutine
280 to end itself, although there is no guarantee that the exception
281 will lead to termination, and if the exception isn't caught it might
282 well end the whole program.
283
284 You might also think of "throw" as being the moral equivalent of
285 "kill"ing a coroutine with a signal (in this case, a scalar).
286
287 $coroutine->join
90 Wait until the coroutine terminates and return any values given to 288 Wait until the coroutine terminates and return any values given to
91 the "terminate" or "cancel" functions. "join" can be called multiple 289 the "terminate" or "cancel" functions. "join" can be called
92 times from multiple processes. 290 concurrently from multiple coroutines, and all will be resumed and
291 given the status return once the $coroutine terminates.
93 292
293 $coroutine->on_destroy (\&cb)
294 Registers a callback that is called when this coroutine gets
295 destroyed, but before it is joined. The callback gets passed the
296 terminate arguments, if any, and *must not* die, under any
297 circumstances.
298
94 $oldprio = $process->prio($newprio) 299 $oldprio = $coroutine->prio ($newprio)
95 Sets (or gets, if the argument is missing) the priority of the 300 Sets (or gets, if the argument is missing) the priority of the
96 process. Higher priority processes get run before lower priority 301 coroutine. Higher priority coroutines get run before lower priority
97 processes. Priorities are small signed integers (currently -4 .. 302 coroutines. Priorities are small signed integers (currently -4 ..
98 +3), that you can refer to using PRIO_xxx constants (use the import 303 +3), that you can refer to using PRIO_xxx constants (use the import
99 tag :prio to get then): 304 tag :prio to get then):
100 305
101 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN 306 PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN
102 3 > 1 > 0 > -1 > -3 > -4 307 3 > 1 > 0 > -1 > -3 > -4
105 current->prio(PRIO_HIGH); 310 current->prio(PRIO_HIGH);
106 311
107 The idle coroutine ($Coro::idle) always has a lower priority than 312 The idle coroutine ($Coro::idle) always has a lower priority than
108 any existing coroutine. 313 any existing coroutine.
109 314
110 Changing the priority of the current process will take effect 315 Changing the priority of the current coroutine will take effect
111 immediately, but changing the priority of processes in the ready 316 immediately, but changing the priority of coroutines in the ready
112 queue (but not running) will only take effect after the next 317 queue (but not running) will only take effect after the next
113 schedule (of that process). This is a bug that will be fixed in some 318 schedule (of that coroutine). This is a bug that will be fixed in
114 future version. 319 some future version.
115 320
116 $newprio = $process->nice($change) 321 $newprio = $coroutine->nice ($change)
117 Similar to "prio", but subtract the given value from the priority 322 Similar to "prio", but subtract the given value from the priority
118 (i.e. higher values mean lower priority, just as in unix). 323 (i.e. higher values mean lower priority, just as in unix).
119 324
120 $olddesc = $process->desc($newdesc) 325 $olddesc = $coroutine->desc ($newdesc)
121 Sets (or gets in case the argument is missing) the description for 326 Sets (or gets in case the argument is missing) the description for
122 this process. This is just a free-form string you can associate with 327 this coroutine. This is just a free-form string you can associate
123 a process. 328 with a coroutine.
329
330 This method simply sets the "$coroutine->{desc}" member to the given
331 string. You can modify this member directly if you wish.
332
333 GLOBAL FUNCTIONS
334 Coro::nready
335 Returns the number of coroutines that are currently in the ready
336 state, i.e. that can be switched to by calling "schedule" directory
337 or indirectly. The value 0 means that the only runnable coroutine is
338 the currently running one, so "cede" would have no effect, and
339 "schedule" would cause a deadlock unless there is an idle handler
340 that wakes up some coroutines.
341
342 my $guard = Coro::guard { ... }
343 This creates and returns a guard object. Nothing happens until the
344 object gets destroyed, in which case the codeblock given as argument
345 will be executed. This is useful to free locks or other resources in
346 case of a runtime error or when the coroutine gets canceled, as in
347 both cases the guard block will be executed. The guard object
348 supports only one method, "->cancel", which will keep the codeblock
349 from being executed.
350
351 Example: set some flag and clear it again when the coroutine gets
352 canceled or the function returns:
353
354 sub do_something {
355 my $guard = Coro::guard { $busy = 0 };
356 $busy = 1;
357
358 # do something that requires $busy to be true
359 }
360
361 unblock_sub { ... }
362 This utility function takes a BLOCK or code reference and "unblocks"
363 it, returning a new coderef. Unblocking means that calling the new
364 coderef will return immediately without blocking, returning nothing,
365 while the original code ref will be called (with parameters) from
366 within another coroutine.
367
368 The reason this function exists is that many event libraries (such
369 as the venerable Event module) are not coroutine-safe (a weaker form
370 of thread-safety). This means you must not block within event
371 callbacks, otherwise you might suffer from crashes or worse. The
372 only event library currently known that is safe to use without
373 "unblock_sub" is EV.
374
375 This function allows your callbacks to block by executing them in
376 another coroutine where it is safe to block. One example where
377 blocking is handy is when you use the Coro::AIO functions to save
378 results to disk, for example.
379
380 In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
381 when creating event callbacks that want to block.
382
383 If your handler does not plan to block (e.g. simply sends a message
384 to another coroutine, or puts some other coroutine into the ready
385 queue), there is no reason to use "unblock_sub".
386
387 Note that you also need to use "unblock_sub" for any other callbacks
388 that are indirectly executed by any C-based event loop. For example,
389 when you use a module that uses AnyEvent (and you use
390 Coro::AnyEvent) and it provides callbacks that are the result of
391 some event callback, then you must not block either, or use
392 "unblock_sub".
393
394 $cb = Coro::rouse_cb
395 Create and return a "rouse callback". That's a code reference that,
396 when called, will save its arguments and notify the owner coroutine
397 of the callback.
398
399 See the next function.
400
401 @args = Coro::rouse_wait [$cb]
402 Wait for the specified rouse callback (or the last one tht was
403 created in this coroutine).
404
405 As soon as the callback is invoked (or when the calback was invoked
406 before "rouse_wait"), it will return a copy of the arguments
407 originally passed to the rouse callback.
408
409 See the section HOW TO WAIT FOR A CALLBACK for an actual usage
410 example.
411
412HOW TO WAIT FOR A CALLBACK
413 It is very common for a coroutine to wait for some callback to be
414 called. This occurs naturally when you use coroutines in an otherwise
415 event-based program, or when you use event-based libraries.
416
417 These typically register a callback for some event, and call that
418 callback when the event occured. In a coroutine, however, you typically
419 want to just wait for the event, simplyifying things.
420
421 For example "AnyEvent->child" registers a callback to be called when a
422 specific child has exited:
423
424 my $child_watcher = AnyEvent->child (pid => $pid, cb => sub { ... });
425
426 But from withina coroutine, you often just want to write this:
427
428 my $status = wait_for_child $pid;
429
430 Coro offers two functions specifically designed to make this easy,
431 "Coro::rouse_cb" and "Coro::rouse_wait".
432
433 The first function, "rouse_cb", generates and returns a callback that,
434 when invoked, will save it's arguments and notify the coroutine that
435 created the callback.
436
437 The second function, "rouse_wait", waits for the callback to be called
438 (by calling "schedule" to go to sleep) and returns the arguments
439 originally passed to the callback.
440
441 Using these functions, it becomes easy to write the "wait_for_child"
442 function mentioned above:
443
444 sub wait_for_child($) {
445 my ($pid) = @_;
446
447 my $watcher = AnyEvent->child (pid => $pid, cb => Coro::rouse_cb);
448
449 my ($rpid, $rstatus) = Coro::rouse_wait;
450 $rstatus
451 }
452
453 In the case where "rouse_cb" and "rouse_wait" are not flexible enough,
454 you can roll your own, using "schedule":
455
456 sub wait_for_child($) {
457 my ($pid) = @_;
458
459 # store the current coroutine in $current,
460 # and provide result variables for the closure passed to ->child
461 my $current = $Coro::current;
462 my ($done, $rstatus);
463
464 # pass a closure to ->child
465 my $watcher = AnyEvent->child (pid => $pid, cb => sub {
466 $rstatus = $_[1]; # remember rstatus
467 $done = 1; # mark $rstatus as valud
468 });
469
470 # wait until the closure has been called
471 schedule while !$done;
472
473 $rstatus
474 }
124 475
125BUGS/LIMITATIONS 476BUGS/LIMITATIONS
126 - you must make very sure that no coro is still active on global 477 fork with pthread backend
127 destruction. very bad things might happen otherwise (usually segfaults). 478 When Coro is compiled using the pthread backend (which isn't
479 recommended but required on many BSDs as their libcs are completely
480 broken), then coroutines will not survive a fork. There is no known
481 workaround except to fix your libc and use a saner backend.
128 482
483 perl process emulation ("threads")
129 - this module is not thread-safe. You should only ever use this module 484 This module is not perl-pseudo-thread-safe. You should only ever use
130 from the same thread (this requirement might be losened in the future 485 this module from the same thread (this requirement might be removed
131 to allow per-thread schedulers, but Coro::State does not yet allow 486 in the future to allow per-thread schedulers, but Coro::State does
132 this). 487 not yet allow this). I recommend disabling thread support and using
488 processes, as having the windows process emulation enabled under
489 unix roughly halves perl performance, even when not used.
490
491 coroutine switching not signal safe
492 You must not switch to another coroutine from within a signal
493 handler (only relevant with %SIG - most event libraries provide safe
494 signals).
495
496 That means you *MUST NOT* call any function that might "block" the
497 current coroutine - "cede", "schedule" "Coro::Semaphore->down" or
498 anything that calls those. Everything else, including calling
499 "ready", works.
133 500
134SEE ALSO 501SEE ALSO
502 Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
503
504 Debugging: Coro::Debug.
505
135 Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util. 506 Support/Utility: Coro::Specific, Coro::Util.
136 507
137 Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, 508 Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
138 Coro::SemaphoreSet, Coro::RWLock. 509 Coro::SemaphoreSet, Coro::RWLock.
139 510
140 Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket, 511 IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
141 Coro::Select.
142 512
143 Embedding: <Coro:MakeMaker> 513 Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
514
515 XS API: Coro::MakeMaker.
516
517 Low level Configuration, Coroutine Environment: Coro::State.
144 518
145AUTHOR 519AUTHOR
146 Marc Lehmann <schmorp@schmorp.de> 520 Marc Lehmann <schmorp@schmorp.de>
147 http://home.schmorp.de/ 521 http://home.schmorp.de/
148 522

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