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Revision 1.36 by root, Sun Jun 7 02:01:04 2015 UTC vs.
Revision 1.41 by root, Fri Aug 23 08:01:13 2019 UTC

66CORO THREAD LIFE CYCLE 66CORO THREAD LIFE CYCLE
67 During the long and exciting (or not) life of a coro thread, it goes 67 During the long and exciting (or not) life of a coro thread, it goes
68 through a number of states: 68 through a number of states:
69 69
70 1. Creation 70 1. Creation
71 The first thing in the life of a coro thread is it's creation - 71 The first thing in the life of a coro thread is its creation -
72 obviously. The typical way to create a thread is to call the "async 72 obviously. The typical way to create a thread is to call the "async
73 BLOCK" function: 73 BLOCK" function:
74 74
75 async { 75 async {
76 # thread code goes here 76 # thread code goes here
85 This creates a new coro thread and puts it into the ready queue, 85 This creates a new coro thread and puts it into the ready queue,
86 meaning it will run as soon as the CPU is free for it. 86 meaning it will run as soon as the CPU is free for it.
87 87
88 "async" will return a Coro object - you can store this for future 88 "async" will return a Coro object - you can store this for future
89 reference or ignore it - a thread that is running, ready to run or 89 reference or ignore it - a thread that is running, ready to run or
90 waiting for some event is alive on it's own. 90 waiting for some event is alive on its own.
91 91
92 Another way to create a thread is to call the "new" constructor with 92 Another way to create a thread is to call the "new" constructor with
93 a code-reference: 93 a code-reference:
94 94
95 new Coro sub { 95 new Coro sub {
239 implements an endless loop, the $guard will not be cleaned up. 239 implements an endless loop, the $guard will not be cleaned up.
240 However, since the thread object returned by "async" is not stored 240 However, since the thread object returned by "async" is not stored
241 anywhere, the thread is initially referenced because it is in the 241 anywhere, the thread is initially referenced because it is in the
242 ready queue, when it runs it is referenced by $Coro::current, but 242 ready queue, when it runs it is referenced by $Coro::current, but
243 when it calls "schedule", it gets "cancel"ed causing the guard 243 when it calls "schedule", it gets "cancel"ed causing the guard
244 object to be destroyed (see the next section), and printing it's 244 object to be destroyed (see the next section), and printing its
245 message. 245 message.
246 246
247 If this seems a bit drastic, remember that this only happens when 247 If this seems a bit drastic, remember that this only happens when
248 nothing references the thread anymore, which means there is no way 248 nothing references the thread anymore, which means there is no way
249 to further execute it, ever. The only options at this point are 249 to further execute it, ever. The only options at this point are
252 5. Cleanup 252 5. Cleanup
253 Threads will allocate various resources. Most but not all will be 253 Threads will allocate various resources. Most but not all will be
254 returned when a thread terminates, during clean-up. 254 returned when a thread terminates, during clean-up.
255 255
256 Cleanup is quite similar to throwing an uncaught exception: perl 256 Cleanup is quite similar to throwing an uncaught exception: perl
257 will work it's way up through all subroutine calls and blocks. On 257 will work its way up through all subroutine calls and blocks. On its
258 it's way, it will release all "my" variables, undo all "local"'s and 258 way, it will release all "my" variables, undo all "local"'s and free
259 free any other resources truly local to the thread. 259 any other resources truly local to the thread.
260 260
261 So, a common way to free resources is to keep them referenced only 261 So, a common way to free resources is to keep them referenced only
262 by my variables: 262 by my variables:
263 263
264 async { 264 async {
284 those code blocks): 284 those code blocks):
285 285
286 async { 286 async {
287 my $window = new Gtk2::Window "toplevel"; 287 my $window = new Gtk2::Window "toplevel";
288 # The window will not be cleaned up automatically, even when $window 288 # The window will not be cleaned up automatically, even when $window
289 # gets freed, so use a guard to ensure it's destruction 289 # gets freed, so use a guard to ensure its destruction
290 # in case of an error: 290 # in case of an error:
291 my $window_guard = Guard::guard { $window->destroy }; 291 my $window_guard = Guard::guard { $window->destroy };
292 292
293 # we are safe here 293 # we are safe here
294 }; 294 };
417 program, as "async" does. As the coro is being reused, stuff like 417 program, as "async" does. As the coro is being reused, stuff like
418 "on_destroy" will not work in the expected way, unless you call 418 "on_destroy" will not work in the expected way, unless you call
419 terminate or cancel, which somehow defeats the purpose of pooling 419 terminate or cancel, which somehow defeats the purpose of pooling
420 (but is fine in the exceptional case). 420 (but is fine in the exceptional case).
421 421
422 The priority will be reset to 0 after each run, tracing will be 422 The priority will be reset to 0 after each run, all "swap_sv" calls
423 disabled, the description will be reset and the default output 423 will be undone, tracing will be disabled, the description will be
424 filehandle gets restored, so you can change all these. Otherwise the 424 reset and the default output filehandle gets restored, so you can
425 coro will be re-used "as-is": most notably if you change other 425 change all these. Otherwise the coro will be re-used "as-is": most
426 per-coro global stuff such as $/ you *must needs* revert that 426 notably if you change other per-coro global stuff such as $/ you
427 change, which is most simply done by using local as in: "local $/". 427 *must needs* revert that change, which is most simply done by using
428 local as in: "local $/".
428 429
429 The idle pool size is limited to 8 idle coros (this can be adjusted 430 The idle pool size is limited to 8 idle coros (this can be adjusted
430 by changing $Coro::POOL_SIZE), but there can be as many non-idle 431 by changing $Coro::POOL_SIZE), but there can be as many non-idle
431 coros as required. 432 coros as required.
432 433
533 # at this place, the timezone is Antarctica/South_Pole, 534 # at this place, the timezone is Antarctica/South_Pole,
534 # without disturbing the TZ of any other coro. 535 # without disturbing the TZ of any other coro.
535 }; 536 };
536 537
537 This can be used to localise about any resource (locale, uid, 538 This can be used to localise about any resource (locale, uid,
538 current working directory etc.) to a block, despite the existance of 539 current working directory etc.) to a block, despite the existence of
539 other coros. 540 other coros.
540 541
541 Another interesting example implements time-sliced multitasking 542 Another interesting example implements time-sliced multitasking
542 using interval timers (this could obviously be optimised, but does 543 using interval timers (this could obviously be optimised, but does
543 the job): 544 the job):
625 $state->is_new 626 $state->is_new
626 Returns true iff this Coro object is "new", i.e. has never been run 627 Returns true iff this Coro object is "new", i.e. has never been run
627 yet. Those states basically consist of only the code reference to 628 yet. Those states basically consist of only the code reference to
628 call and the arguments, but consumes very little other resources. 629 call and the arguments, but consumes very little other resources.
629 New states will automatically get assigned a perl interpreter when 630 New states will automatically get assigned a perl interpreter when
630 they are transfered to. 631 they are transferred to.
631 632
632 $state->is_zombie 633 $state->is_zombie
633 Returns true iff the Coro object has been cancelled, i.e. it's 634 Returns true iff the Coro object has been cancelled, i.e. its
634 resources freed because they were "cancel"'ed, "terminate"'d, 635 resources freed because they were "cancel"'ed, "terminate"'d,
635 "safe_cancel"'ed or simply went out of scope. 636 "safe_cancel"'ed or simply went out of scope.
636 637
637 The name "zombie" stems from UNIX culture, where a process that has 638 The name "zombie" stems from UNIX culture, where a process that has
638 exited and only stores and exit status and no other resources is 639 exited and only stores and exit status and no other resources is
650 651
651 $is_suspended = $coro->is_suspended 652 $is_suspended = $coro->is_suspended
652 Returns true iff this Coro object has been suspended. Suspended 653 Returns true iff this Coro object has been suspended. Suspended
653 Coros will not ever be scheduled. 654 Coros will not ever be scheduled.
654 655
655 $coro->cancel (arg...) 656 $coro->cancel ($arg...)
656 Terminates the given Coro thread and makes it return the given 657 Terminate the given Coro thread and make it return the given
657 arguments as status (default: an empty list). Never returns if the 658 arguments as status (default: an empty list). Never returns if the
658 Coro is the current Coro. 659 Coro is the current Coro.
659 660
660 This is a rather brutal way to free a coro, with some limitations - 661 This is a rather brutal way to free a coro, with some limitations -
661 if the thread is inside a C callback that doesn't expect to be 662 if the thread is inside a C callback that doesn't expect to be
696 context and can block if they wish. The downside is that there is no 697 context and can block if they wish. The downside is that there is no
697 guarantee that the thread can be cancelled when you call this 698 guarantee that the thread can be cancelled when you call this
698 method, and therefore, it might fail. It is also considerably slower 699 method, and therefore, it might fail. It is also considerably slower
699 than "cancel" or "terminate". 700 than "cancel" or "terminate".
700 701
701 A thread is in a safe-cancellable state if it either hasn't been run 702 A thread is in a safe-cancellable state if it either has never been
703 run yet, has already been canceled/terminated or otherwise
702 yet, or it has no C context attached and is inside an SLF function. 704 destroyed, or has no C context attached and is inside an SLF
705 function.
703 706
707 The first two states are trivial - a thread that hasnot started or
708 has already finished is safe to cancel.
709
704 The latter two basically mean that the thread isn't currently inside 710 The last state basically means that the thread isn't currently
705 a perl callback called from some C function (usually via some XS 711 inside a perl callback called from some C function (usually via some
706 modules) and isn't currently executing inside some C function itself 712 XS modules) and isn't currently executing inside some C function
707 (via Coro's XS API). 713 itself (via Coro's XS API).
708 714
709 This call returns true when it could cancel the thread, or croaks 715 This call returns true when it could cancel the thread, or croaks
710 with an error otherwise (i.e. it either returns true or doesn't 716 with an error otherwise (i.e. it either returns true or doesn't
711 return at all). 717 return at all).
712 718
777 from multiple threads, and all will be resumed and given the status 783 from multiple threads, and all will be resumed and given the status
778 return once the $coro terminates. 784 return once the $coro terminates.
779 785
780 $coro->on_destroy (\&cb) 786 $coro->on_destroy (\&cb)
781 Registers a callback that is called when this coro thread gets 787 Registers a callback that is called when this coro thread gets
782 destroyed, that is, after it's resources have been freed but before 788 destroyed, that is, after its resources have been freed but before
783 it is joined. The callback gets passed the terminate/cancel 789 it is joined. The callback gets passed the terminate/cancel
784 arguments, if any, and *must not* die, under any circumstances. 790 arguments, if any, and *must not* die, under any circumstances.
785 791
786 There can be any number of "on_destroy" callbacks per coro, and 792 There can be any number of "on_destroy" callbacks per coro, and
787 there is currently no way to remove a callback once added. 793 there is currently no way to remove a callback once added.
906 It is very common for a coro to wait for some callback to be called. 912 It is very common for a coro to wait for some callback to be called.
907 This occurs naturally when you use coro in an otherwise event-based 913 This occurs naturally when you use coro in an otherwise event-based
908 program, or when you use event-based libraries. 914 program, or when you use event-based libraries.
909 915
910 These typically register a callback for some event, and call that 916 These typically register a callback for some event, and call that
911 callback when the event occured. In a coro, however, you typically want 917 callback when the event occurred. In a coro, however, you typically want
912 to just wait for the event, simplyifying things. 918 to just wait for the event, simplyifying things.
913 919
914 For example "AnyEvent->child" registers a callback to be called when a 920 For example "AnyEvent->child" registers a callback to be called when a
915 specific child has exited: 921 specific child has exited:
916 922
1035 processes. What makes it so bad is that on non-windows platforms, you 1041 processes. What makes it so bad is that on non-windows platforms, you
1036 can actually take advantage of custom hardware for this purpose (as 1042 can actually take advantage of custom hardware for this purpose (as
1037 evidenced by the forks module, which gives you the (i-) threads API, 1043 evidenced by the forks module, which gives you the (i-) threads API,
1038 just much faster). 1044 just much faster).
1039 1045
1040 Sharing data is in the i-threads model is done by transfering data 1046 Sharing data is in the i-threads model is done by transferring data
1041 structures between threads using copying semantics, which is very slow - 1047 structures between threads using copying semantics, which is very slow -
1042 shared data simply does not exist. Benchmarks using i-threads which are 1048 shared data simply does not exist. Benchmarks using i-threads which are
1043 communication-intensive show extremely bad behaviour with i-threads (in 1049 communication-intensive show extremely bad behaviour with i-threads (in
1044 fact, so bad that Coro, which cannot take direct advantage of multiple 1050 fact, so bad that Coro, which cannot take direct advantage of multiple
1045 CPUs, is often orders of magnitude faster because it shares data using 1051 CPUs, is often orders of magnitude faster because it shares data using
1074 1080
1075 XS API: Coro::MakeMaker. 1081 XS API: Coro::MakeMaker.
1076 1082
1077 Low level Configuration, Thread Environment, Continuations: Coro::State. 1083 Low level Configuration, Thread Environment, Continuations: Coro::State.
1078 1084
1079AUTHOR 1085AUTHOR/SUPPORT/CONTACT
1080 Marc Lehmann <schmorp@schmorp.de> 1086 Marc A. Lehmann <schmorp@schmorp.de>
1081 http://home.schmorp.de/ 1087 http://software.schmorp.de/pkg/Coro.html
1082 1088

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