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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 coroutine 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 at the same time even on SMP machines. 29 threads but don't (in general) run in parallel at the same time even on
22 The specific flavor of coroutine use din this module also guarentees you 30 SMP machines. The specific flavor of coroutine used in this module also
23 that it will not switch between coroutines unless necessary, at 31 guarantees you that it will not switch between coroutines unless
24 easily-identified points in your program, so locking and parallel access 32 necessary, at easily-identified points in your program, so locking and
25 are rarely an issue, making coroutine programming much safer than 33 parallel access are rarely an issue, making coroutine programming much
26 threads programming. 34 safer and easier than threads programming.
27 35
28 (Perl, however, does not natively support real threads but instead does 36 Unlike a normal perl program, however, coroutines allow you to have
29 a very slow and memory-intensive emulation of processes using threads. 37 multiple running interpreters that share data, which is especially
30 This is a performance win on Windows machines, and a loss everywhere 38 useful to code pseudo-parallel processes and for event-based
31 else). 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).
32 49
33 In this module, coroutines are defined as "callchain + lexical variables 50 In this module, coroutines are defined as "callchain + lexical variables
34 + @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own 51 + @_ + $_ + $@ + $/ + C stack), that is, a coroutine has its own
35 callchain, its own set of lexicals and its own set of perls most 52 callchain, its own set of lexicals and its own set of perls most
36 important global variables. 53 important global variables (see Coro::State for more configuration).
37 54
38 $main 55 $Coro::main
39 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.
40 61
41 $current (or as function: current) 62 $Coro::current
42 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
43 value is $main (of course). 65 $main (of course).
44 66
45 This variable is strictly *read-only*. It is provided for 67 This variable is strictly *read-only*. You can take copies of the
46 performance reasons. If performance is not essentiel you are 68 value stored in it and use it as any other coroutine object, but you
47 encouraged to use the "Coro::current" function instead. 69 must not otherwise modify the variable itself.
48 70
49 $idle 71 $Coro::idle
50 A callback that is called whenever the scheduler finds no ready 72 This variable is mainly useful to integrate Coro into event loops.
51 coroutines to run. The default implementation prints "FATAL: 73 It is usually better to rely on Coro::AnyEvent or L"Coro::EV", as
52 deadlock detected" and exits, because the program has no other way 74 this is pretty low-level functionality.
53 to continue. 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.
54 80
55 This hook is overwritten by modules such as "Coro::Timer" and 81 This hook is overwritten by modules such as "Coro::Timer" and
56 "Coro::Event" to wait on an external event that hopefully wake up a 82 "Coro::AnyEvent" to wait on an external event that hopefully wake up
57 coroutine so the scheduler can run it. 83 a coroutine so the scheduler can run it.
84
85 Note that the callback *must not*, under any circumstances, block
86 the current coroutine. Normally, this is achieved by having an "idle
87 coroutine" that calls the event loop and then blocks again, and then
88 readying that coroutine in the idle handler.
89
90 See Coro::Event or Coro::AnyEvent for examples of using this
91 technique.
58 92
59 Please note that if your callback recursively invokes perl (e.g. for 93 Please note that if your callback recursively invokes perl (e.g. for
60 event handlers), then it must be prepared to be called recursively. 94 event handlers), then it must be prepared to be called recursively
95 itself.
61 96
62 STATIC METHODS 97 SIMPLE COROUTINE CREATION
63 Static methods are actually functions that operate on the current
64 coroutine only.
65
66 async { ... } [@args...] 98 async { ... } [@args...]
67 Create a new asynchronous coroutine and return it's coroutine object 99 Create a new coroutine and return it's coroutine object (usually
68 (usually unused). When the sub returns the new coroutine 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
69 automatically terminated. 105 automatically terminated.
70 106
71 Calling "exit" in a coroutine will not work correctly, so do not do 107 The remaining arguments are passed as arguments to the closure.
72 that.
73 108
74 When the coroutine dies, the program will exit, just as in the main 109 See the "Coro::State::new" constructor for info about the coroutine
75 program. 110 environment in which coroutines are executed.
76 111
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
77 # create a new coroutine that just prints its arguments 119 Example: Create a new coroutine that just prints its arguments.
120
78 async { 121 async {
79 print "@_\n"; 122 print "@_\n";
80 } 1,2,3,4; 123 } 1,2,3,4;
81 124
82 async_pool { ... } [@args...] 125 async_pool { ... } [@args...]
83 Similar to "async", but uses a coroutine pool, so you should not 126 Similar to "async", but uses a coroutine pool, so you should not
84 call terminate or join (although you are allowed to), and you get a 127 call terminate or join on it (although you are allowed to), and you
85 coroutine that might have executed other code already (which can be 128 get a coroutine that might have executed other code already (which
86 good or bad :). 129 can be good or bad :).
87 130
131 On the plus side, this function is faster than creating (and
132 destroying) a completly new coroutine, so if you need a lot of
133 generic coroutines in quick successsion, use "async_pool", not
134 "async".
135
88 Also, the block is executed in an "eval" context and a warning will 136 The code block is executed in an "eval" context and a warning will
89 be issued in case of an exception instead of terminating the 137 be issued in case of an exception instead of terminating the
90 program, as "async" does. As the coroutine is being reused, stuff 138 program, as "async" does. As the coroutine is being reused, stuff
91 like "on_destroy" will not work in the expected way, unless you call 139 like "on_destroy" will not work in the expected way, unless you call
92 terminate or cancel, which somehow defeats the purpose of pooling. 140 terminate or cancel, which somehow defeats the purpose of pooling
141 (but is fine in the exceptional case).
93 142
94 The priority will be reset to 0 after each job, otherwise the 143 The priority will be reset to 0 after each run, tracing will be
95 coroutine will be re-used "as-is". 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 $/".
96 149
97 The pool size is limited to 8 idle coroutines (this can be adjusted 150 The idle pool size is limited to 8 idle coroutines (this can be
98 by changing $Coro::POOL_SIZE), and there can be as many non-idle 151 adjusted by changing $Coro::POOL_SIZE), but there can be as many
99 coros as required. 152 non-idle coros as required.
100 153
101 If you are concerned about pooled coroutines growing a lot because a 154 If you are concerned about pooled coroutines growing a lot because a
102 single "async_pool" used a lot of stackspace you can e.g. 155 single "async_pool" used a lot of stackspace you can e.g.
103 "async_pool { terminate }" once per second or so to slowly replenish 156 "async_pool { terminate }" once per second or so to slowly replenish
104 the pool. 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.
105 164
106 schedule 165 schedule
107 Calls the scheduler. Please note that the current coroutine 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
108 be put into the ready queue, so calling this function usually means 173 ready queue, so calling this function usually means you will never
109 you will never be called again unless something else (e.g. an event 174 be called again unless something else (e.g. an event handler) calls
110 handler) calls ready. 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.
111 184
112 The canonical way to wait on external events is this: 185 The canonical way to wait on external events is this:
113 186
114 { 187 {
115 # remember current coroutine 188 # remember current coroutine
120 # wake up sleeping coroutine 193 # wake up sleeping coroutine
121 $current->ready; 194 $current->ready;
122 undef $current; 195 undef $current;
123 }; 196 };
124 197
125 # call schedule until event occured. 198 # call schedule until event occurred.
126 # in case we are woken up for other reasons 199 # in case we are woken up for other reasons
127 # (current still defined), loop. 200 # (current still defined), loop.
128 Coro::schedule while $current; 201 Coro::schedule while $current;
129 } 202 }
130 203
131 cede 204 cede
132 "Cede" to other coroutines. This function puts the current coroutine 205 "Cede" to other coroutines. This function puts the current coroutine
133 into the ready queue and calls "schedule", which has the effect of 206 into the ready queue and calls "schedule", which has the effect of
134 giving up the current "timeslice" to other coroutines of the same or 207 giving up the current "timeslice" to other coroutines of the same or
135 higher priority. 208 higher priority. Once your coroutine gets its turn again it will
209 automatically be resumed.
136 210
137 Returns true if at least one coroutine switch has happened. 211 This function is often called "yield" in other languages.
138 212
139 Coro::cede_notself 213 Coro::cede_notself
140 Works like cede, but is not exported by default and will cede to any 214 Works like cede, but is not exported by default and will cede to
141 coroutine, regardless of priority, once. 215 *any* coroutine, regardless of priority. This is useful sometimes to
142 216 ensure progress is made.
143 Returns true if at least one coroutine switch has happened.
144 217
145 terminate [arg...] 218 terminate [arg...]
146 Terminates the current coroutine with the given status values (see 219 Terminates the current coroutine with the given status values (see
147 cancel). 220 cancel).
148 221
149 # dynamic methods 222 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 Note that while this will try to free some of the main programs
228 resources, you cannot 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.
150 231
151 COROUTINE METHODS 232 COROUTINE METHODS
152 These are the methods you can call on coroutine objects. 233 These are the methods you can call on coroutine objects (or to create
234 them).
153 235
154 new Coro \&sub [, @args...] 236 new Coro \&sub [, @args...]
155 Create a new coroutine and return it. When the sub returns the 237 Create a new coroutine and return it. When the sub returns, the
156 coroutine automatically terminates as if "terminate" with the 238 coroutine automatically terminates as if "terminate" with the
157 returned values were called. To make the coroutine run you must 239 returned values were called. To make the coroutine run you must
158 first put it into the ready queue by calling the ready method. 240 first put it into the ready queue by calling the ready method.
159 241
160 Calling "exit" in a coroutine will not work correctly, so do not do 242 See "async" and "Coro::State::new" for additional info about the
161 that. 243 coroutine environment.
162 244
163 $success = $coroutine->ready 245 $success = $coroutine->ready
164 Put the given coroutine into the ready queue (according to it's 246 Put the given coroutine into the end of its ready queue (there is
165 priority) and return true. If the coroutine is already in the ready 247 one queue for each priority) and return true. If the coroutine is
166 queue, do nothing and return false. 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.
167 254
168 $is_ready = $coroutine->is_ready 255 $is_ready = $coroutine->is_ready
169 Return wether the coroutine is currently the ready queue or not, 256 Return whether the coroutine is currently the ready queue or not,
170 257
171 $coroutine->cancel (arg...) 258 $coroutine->cancel (arg...)
172 Terminates the given coroutine and makes it return the given 259 Terminates the given coroutine and makes it return the given
173 arguments as status (default: the empty list). Never returns if the 260 arguments as status (default: the empty list). Never returns if the
174 coroutine is the current coroutine. 261 coroutine is the current coroutine.
175 262
263 $coroutine->throw ([$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
176 $coroutine->join 281 $coroutine->join
177 Wait until the coroutine terminates and return any values given to 282 Wait until the coroutine terminates and return any values given to
178 the "terminate" or "cancel" functions. "join" can be called multiple 283 the "terminate" or "cancel" functions. "join" can be called
179 times from multiple coroutine. 284 concurrently from multiple coroutines, and all will be resumed and
285 given the status return once the $coroutine terminates.
180 286
181 $coroutine->on_destroy (\&cb) 287 $coroutine->on_destroy (\&cb)
182 Registers a callback that is called when this coroutine gets 288 Registers a callback that is called when this coroutine gets
183 destroyed, but before it is joined. The callback gets passed the 289 destroyed, but before it is joined. The callback gets passed the
184 terminate arguments, if any. 290 terminate arguments, if any, and *must not* die, under any
291 circumstances.
185 292
186 $oldprio = $coroutine->prio ($newprio) 293 $oldprio = $coroutine->prio ($newprio)
187 Sets (or gets, if the argument is missing) the priority of the 294 Sets (or gets, if the argument is missing) the priority of the
188 coroutine. Higher priority coroutines get run before lower priority 295 coroutine. Higher priority coroutines get run before lower priority
189 coroutines. Priorities are small signed integers (currently -4 .. 296 coroutines. Priorities are small signed integers (currently -4 ..
212 $olddesc = $coroutine->desc ($newdesc) 319 $olddesc = $coroutine->desc ($newdesc)
213 Sets (or gets in case the argument is missing) the description for 320 Sets (or gets in case the argument is missing) the description for
214 this coroutine. This is just a free-form string you can associate 321 this coroutine. This is just a free-form string you can associate
215 with a coroutine. 322 with a coroutine.
216 323
324 This method simply sets the "$coroutine->{desc}" member to the given
325 string. You can modify this member directly if you wish.
326
217 GLOBAL FUNCTIONS 327 GLOBAL FUNCTIONS
218 Coro::nready 328 Coro::nready
219 Returns the number of coroutines that are currently in the ready 329 Returns the number of coroutines that are currently in the ready
220 state, i.e. that can be swicthed to. The value 0 means that the only 330 state, i.e. that can be switched to by calling "schedule" directory
221 runnable coroutine is the currently running one, so "cede" would 331 or indirectly. The value 0 means that the only runnable coroutine is
222 have no effect, and "schedule" would cause a deadlock unless there 332 the currently running one, so "cede" would have no effect, and
333 "schedule" would cause a deadlock unless there is an idle handler
223 is an idle handler that wakes up some coroutines. 334 that wakes up some coroutines.
224 335
225 my $guard = Coro::guard { ... } 336 my $guard = Coro::guard { ... }
226 This creates and returns a guard object. Nothing happens until the 337 This creates and returns a guard object. Nothing happens until the
227 objetc gets destroyed, in which case the codeblock given as argument 338 object gets destroyed, in which case the codeblock given as argument
228 will be executed. This is useful to free locks or other resources in 339 will be executed. This is useful to free locks or other resources in
229 case of a runtime error or when the coroutine gets canceled, as in 340 case of a runtime error or when the coroutine gets canceled, as in
230 both cases the guard block will be executed. The guard object 341 both cases the guard block will be executed. The guard object
231 supports only one method, "->cancel", which will keep the codeblock 342 supports only one method, "->cancel", which will keep the codeblock
232 from being executed. 343 from being executed.
241 # do something that requires $busy to be true 352 # do something that requires $busy to be true
242 } 353 }
243 354
244 unblock_sub { ... } 355 unblock_sub { ... }
245 This utility function takes a BLOCK or code reference and "unblocks" 356 This utility function takes a BLOCK or code reference and "unblocks"
246 it, returning the new coderef. This means that the new coderef will 357 it, returning a new coderef. Unblocking means that calling the new
247 return immediately without blocking, returning nothing, while the 358 coderef will return immediately without blocking, returning nothing,
248 original code ref will be called (with parameters) from within its 359 while the original code ref will be called (with parameters) from
249 own coroutine. 360 within another coroutine.
250 361
251 The reason this fucntion exists is that many event libraries (such 362 The reason this function exists is that many event libraries (such
252 as the venerable Event module) are not coroutine-safe (a weaker form 363 as the venerable Event module) are not coroutine-safe (a weaker form
253 of thread-safety). This means you must not block within event 364 of thread-safety). This means you must not block within event
254 callbacks, otherwise you might suffer from crashes or worse. 365 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.
255 368
256 This function allows your callbacks to block by executing them in 369 This function allows your callbacks to block by executing them in
257 another coroutine where it is safe to block. One example where 370 another coroutine where it is safe to block. One example where
258 blocking is handy is when you use the Coro::AIO functions to save 371 blocking is handy is when you use the Coro::AIO functions to save
259 results to disk. 372 results to disk, for example.
260 373
261 In short: simply use "unblock_sub { ... }" instead of "sub { ... }" 374 In short: simply use "unblock_sub { ... }" instead of "sub { ... }"
262 when creating event callbacks that want to block. 375 when creating event callbacks that want to block.
263 376
377 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
264BUGS/LIMITATIONS 388BUGS/LIMITATIONS
265 - you must make very sure that no coro is still active on global
266 destruction. very bad things might happen otherwise (usually segfaults).
267
268 - this module is not thread-safe. You should only ever use this module 389 This module is not perl-pseudo-thread-safe. You should only ever use
269 from the same thread (this requirement might be losened in the future 390 this module from the same thread (this requirement might be removed in
270 to allow per-thread schedulers, but Coro::State does not yet allow 391 the future to allow per-thread schedulers, but Coro::State does not yet
271 this). 392 allow this). I recommend disabling thread support and using processes,
393 as this is much faster and uses less memory.
272 394
273SEE ALSO 395SEE ALSO
396 Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event.
397
398 Debugging: Coro::Debug.
399
274 Support/Utility: Coro::Cont, Coro::Specific, Coro::State, Coro::Util. 400 Support/Utility: Coro::Specific, Coro::Util.
275 401
276 Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore, 402 Locking/IPC: Coro::Signal, Coro::Channel, Coro::Semaphore,
277 Coro::SemaphoreSet, Coro::RWLock. 403 Coro::SemaphoreSet, Coro::RWLock.
278 404
279 Event/IO: Coro::Timer, Coro::Event, Coro::Handle, Coro::Socket, 405 IO/Timers: Coro::Timer, Coro::Handle, Coro::Socket, Coro::AIO.
280 Coro::Select.
281 406
282 Embedding: <Coro:MakeMaker> 407 Compatibility: Coro::LWP, Coro::BDB, Coro::Storable, Coro::Select.
408
409 XS API: Coro::MakeMaker.
410
411 Low level Configuration, Coroutine Environment: Coro::State.
283 412
284AUTHOR 413AUTHOR
285 Marc Lehmann <schmorp@schmorp.de> 414 Marc Lehmann <schmorp@schmorp.de>
286 http://home.schmorp.de/ 415 http://home.schmorp.de/
287 416

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