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37 | easily-identified points in your program, so locking and parallel access |
37 | easily-identified points in your program, so locking and parallel access |
38 | are rarely an issue, making thread programming much safer and easier |
38 | are rarely an issue, making thread programming much safer and easier |
39 | than using other thread models. |
39 | than using other thread models. |
40 | |
40 | |
41 | Unlike the so-called "Perl threads" (which are not actually real threads |
41 | Unlike the so-called "Perl threads" (which are not actually real threads |
42 | but only the windows process emulation ported to unix, and as such act |
42 | but only the windows process emulation (see section of same name for |
43 | as processes), Coro provides a full shared address space, which makes |
43 | more details) ported to unix, and as such act as processes), Coro |
44 | communication between threads very easy. And Coro's threads are fast, |
44 | provides a full shared address space, which makes communication between |
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45 | threads very easy. And Coro's threads are fast, too: disabling the |
45 | too: disabling the Windows process emulation code in your perl and using |
46 | Windows process emulation code in your perl and using Coro can easily |
46 | Coro can easily result in a two to four times speed increase for your |
47 | result in a two to four times speed increase for your programs. A |
47 | programs. A parallel matrix multiplication benchmark runs over 300 times |
48 | parallel matrix multiplication benchmark runs over 300 times faster on a |
48 | faster on a single core than perl's pseudo-threads on a quad core using |
49 | single core than perl's pseudo-threads on a quad core using all four |
49 | all four cores. |
50 | cores. |
50 | |
51 | |
51 | Coro achieves that by supporting multiple running interpreters that |
52 | Coro achieves that by supporting multiple running interpreters that |
52 | share data, which is especially useful to code pseudo-parallel processes |
53 | share data, which is especially useful to code pseudo-parallel processes |
53 | and for event-based programming, such as multiple HTTP-GET requests |
54 | and for event-based programming, such as multiple HTTP-GET requests |
54 | running concurrently. See Coro::AnyEvent to learn more on how to |
55 | running concurrently. See Coro::AnyEvent to learn more on how to |
… | |
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82 | $Coro::idle |
83 | $Coro::idle |
83 | This variable is mainly useful to integrate Coro into event loops. |
84 | This variable is mainly useful to integrate Coro into event loops. |
84 | It is usually better to rely on Coro::AnyEvent or Coro::EV, as this |
85 | It is usually better to rely on Coro::AnyEvent or Coro::EV, as this |
85 | is pretty low-level functionality. |
86 | is pretty low-level functionality. |
86 | |
87 | |
87 | This variable stores either a Coro object or a callback. |
88 | This variable stores a Coro object that is put into the ready queue |
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89 | when there are no other ready threads (without invoking any ready |
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90 | hooks). |
88 | |
91 | |
89 | If it is a callback, the it is called whenever the scheduler finds |
92 | The default implementation dies with "FATAL: deadlock detected.", |
90 | no ready coros to run. The default implementation prints "FATAL: |
93 | followed by a thread listing, because the program has no other way |
91 | deadlock detected" and exits, because the program has no other way |
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92 | to continue. |
94 | to continue. |
93 | |
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94 | If it is a coro object, then this object will be readied (without |
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95 | invoking any ready hooks, however) when the scheduler finds no other |
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96 | ready coros to run. |
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97 | |
95 | |
98 | This hook is overwritten by modules such as "Coro::EV" and |
96 | This hook is overwritten by modules such as "Coro::EV" and |
99 | "Coro::AnyEvent" to wait on an external event that hopefully wake up |
97 | "Coro::AnyEvent" to wait on an external event that hopefully wake up |
100 | a coro so the scheduler can run it. |
98 | a coro so the scheduler can run it. |
101 | |
99 | |
102 | Note that the callback *must not*, under any circumstances, block |
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103 | the current coro. Normally, this is achieved by having an "idle |
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104 | coro" that calls the event loop and then blocks again, and then |
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105 | readying that coro in the idle handler, or by simply placing the |
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106 | idle coro in this variable. |
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107 | |
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108 | See Coro::Event or Coro::AnyEvent for examples of using this |
100 | See Coro::EV or Coro::AnyEvent for examples of using this technique. |
109 | technique. |
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110 | |
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111 | Please note that if your callback recursively invokes perl (e.g. for |
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112 | event handlers), then it must be prepared to be called recursively |
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113 | itself. |
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114 | |
101 | |
115 | SIMPLE CORO CREATION |
102 | SIMPLE CORO CREATION |
116 | async { ... } [@args...] |
103 | async { ... } [@args...] |
117 | Create a new coro and return its Coro object (usually unused). The |
104 | Create a new coro and return its Coro object (usually unused). The |
118 | coro will be put into the ready queue, so it will start running |
105 | coro will be put into the ready queue, so it will start running |
… | |
… | |
181 | |
168 | |
182 | schedule |
169 | schedule |
183 | Calls the scheduler. The scheduler will find the next coro that is |
170 | Calls the scheduler. The scheduler will find the next coro that is |
184 | to be run from the ready queue and switches to it. The next coro to |
171 | to be run from the ready queue and switches to it. The next coro to |
185 | be run is simply the one with the highest priority that is longest |
172 | be run is simply the one with the highest priority that is longest |
186 | in its ready queue. If there is no coro ready, it will clal the |
173 | in its ready queue. If there is no coro ready, it will call the |
187 | $Coro::idle hook. |
174 | $Coro::idle hook. |
188 | |
175 | |
189 | Please note that the current coro will *not* be put into the ready |
176 | Please note that the current coro will *not* be put into the ready |
190 | queue, so calling this function usually means you will never be |
177 | queue, so calling this function usually means you will never be |
191 | called again unless something else (e.g. an event handler) calls |
178 | called again unless something else (e.g. an event handler) calls |
… | |
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487 | reentrancy). This means you must not block within event callbacks, |
474 | reentrancy). This means you must not block within event callbacks, |
488 | otherwise you might suffer from crashes or worse. The only event |
475 | otherwise you might suffer from crashes or worse. The only event |
489 | library currently known that is safe to use without "unblock_sub" is |
476 | library currently known that is safe to use without "unblock_sub" is |
490 | EV. |
477 | EV. |
491 | |
478 | |
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479 | Coro will try to catch you when you block in the event loop |
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480 | ("FATAL:$Coro::IDLE blocked itself"), but this is just best effort |
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481 | and only works when you do not run your own event loop. |
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482 | |
492 | This function allows your callbacks to block by executing them in |
483 | This function allows your callbacks to block by executing them in |
493 | another coro where it is safe to block. One example where blocking |
484 | another coro where it is safe to block. One example where blocking |
494 | is handy is when you use the Coro::AIO functions to save results to |
485 | is handy is when you use the Coro::AIO functions to save results to |
495 | disk, for example. |
486 | disk, for example. |
496 | |
487 | |
… | |
… | |
506 | when you use a module that uses AnyEvent (and you use |
497 | when you use a module that uses AnyEvent (and you use |
507 | Coro::AnyEvent) and it provides callbacks that are the result of |
498 | Coro::AnyEvent) and it provides callbacks that are the result of |
508 | some event callback, then you must not block either, or use |
499 | some event callback, then you must not block either, or use |
509 | "unblock_sub". |
500 | "unblock_sub". |
510 | |
501 | |
511 | $cb = Coro::rouse_cb |
502 | $cb = rouse_cb |
512 | Create and return a "rouse callback". That's a code reference that, |
503 | Create and return a "rouse callback". That's a code reference that, |
513 | when called, will remember a copy of its arguments and notify the |
504 | when called, will remember a copy of its arguments and notify the |
514 | owner coro of the callback. |
505 | owner coro of the callback. |
515 | |
506 | |
516 | See the next function. |
507 | See the next function. |
517 | |
508 | |
518 | @args = Coro::rouse_wait [$cb] |
509 | @args = rouse_wait [$cb] |
519 | Wait for the specified rouse callback (or the last one that was |
510 | Wait for the specified rouse callback (or the last one that was |
520 | created in this coro). |
511 | created in this coro). |
521 | |
512 | |
522 | As soon as the callback is invoked (or when the callback was invoked |
513 | As soon as the callback is invoked (or when the callback was invoked |
523 | before "rouse_wait"), it will return the arguments originally passed |
514 | before "rouse_wait"), it will return the arguments originally passed |
… | |
… | |
608 | unix roughly halves perl performance, even when not used. |
599 | unix roughly halves perl performance, even when not used. |
609 | |
600 | |
610 | coro switching is not signal safe |
601 | coro switching is not signal safe |
611 | You must not switch to another coro from within a signal handler |
602 | You must not switch to another coro from within a signal handler |
612 | (only relevant with %SIG - most event libraries provide safe |
603 | (only relevant with %SIG - most event libraries provide safe |
613 | signals). |
604 | signals), *unless* you are sure you are not interrupting a Coro |
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605 | function. |
614 | |
606 | |
615 | That means you *MUST NOT* call any function that might "block" the |
607 | That means you *MUST NOT* call any function that might "block" the |
616 | current coro - "cede", "schedule" "Coro::Semaphore->down" or |
608 | current coro - "cede", "schedule" "Coro::Semaphore->down" or |
617 | anything that calls those. Everything else, including calling |
609 | anything that calls those. Everything else, including calling |
618 | "ready", works. |
610 | "ready", works. |
619 | |
611 | |
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612 | WINDOWS PROCESS EMULATION |
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613 | A great many people seem to be confused about ithreads (for example, |
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614 | Chip Salzenberg called me unintelligent, incapable, stupid and gullible, |
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615 | while in the same mail making rather confused statements about perl |
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616 | ithreads (for example, that memory or files would be shared), showing |
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617 | his lack of understanding of this area - if it is hard to understand for |
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618 | Chip, it is probably not obvious to everybody). |
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619 | |
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620 | What follows is an ultra-condensed version of my talk about threads in |
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621 | scripting languages given onthe perl workshop 2009: |
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622 | |
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623 | The so-called "ithreads" were originally implemented for two reasons: |
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624 | first, to (badly) emulate unix processes on native win32 perls, and |
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625 | secondly, to replace the older, real thread model ("5.005-threads"). |
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626 | |
|
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627 | It does that by using threads instead of OS processes. The difference |
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628 | between processes and threads is that threads share memory (and other |
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629 | state, such as files) between threads within a single process, while |
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630 | processes do not share anything (at least not semantically). That means |
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631 | that modifications done by one thread are seen by others, while |
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632 | modifications by one process are not seen by other processes. |
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633 | |
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634 | The "ithreads" work exactly like that: when creating a new ithreads |
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635 | process, all state is copied (memory is copied physically, files and |
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636 | code is copied logically). Afterwards, it isolates all modifications. On |
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637 | UNIX, the same behaviour can be achieved by using operating system |
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638 | processes, except that UNIX typically uses hardware built into the |
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639 | system to do this efficiently, while the windows process emulation |
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640 | emulates this hardware in software (rather efficiently, but of course it |
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641 | is still much slower than dedicated hardware). |
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642 | |
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643 | As mentioned before, loading code, modifying code, modifying data |
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644 | structures and so on is only visible in the ithreads process doing the |
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645 | modification, not in other ithread processes within the same OS process. |
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646 | |
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647 | This is why "ithreads" do not implement threads for perl at all, only |
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648 | processes. What makes it so bad is that on non-windows platforms, you |
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649 | can actually take advantage of custom hardware for this purpose (as |
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650 | evidenced by the forks module, which gives you the (i-) threads API, |
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651 | just much faster). |
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652 | |
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653 | Sharing data is in the i-threads model is done by transfering data |
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654 | structures between threads using copying semantics, which is very slow - |
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655 | shared data simply does not exist. Benchmarks using i-threads which are |
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656 | communication-intensive show extremely bad behaviour with i-threads (in |
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657 | fact, so bad that Coro, which cannot take direct advantage of multiple |
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658 | CPUs, is often orders of magnitude faster because it shares data using |
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659 | real threads, refer to my talk for details). |
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660 | |
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661 | As summary, i-threads *use* threads to implement processes, while the |
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662 | compatible forks module *uses* processes to emulate, uhm, processes. |
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663 | I-threads slow down every perl program when enabled, and outside of |
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664 | windows, serve no (or little) practical purpose, but disadvantages every |
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665 | single-threaded Perl program. |
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666 | |
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667 | This is the reason that I try to avoid the name "ithreads", as it is |
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668 | misleading as it implies that it implements some kind of thread model |
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669 | for perl, and prefer the name "windows process emulation", which |
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670 | describes the actual use and behaviour of it much better. |
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671 | |
620 | SEE ALSO |
672 | SEE ALSO |
621 | Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
673 | Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
622 | |
674 | |
623 | Debugging: Coro::Debug. |
675 | Debugging: Coro::Debug. |
624 | |
676 | |