… | |
… | |
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 |
… | |
… | |
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 |
… | |
… | |
424 | "terminate" or "cancel" functions. "join" can be called concurrently |
411 | "terminate" or "cancel" functions. "join" can be called concurrently |
425 | from multiple coro, and all will be resumed and given the status |
412 | from multiple coro, and all will be resumed and given the status |
426 | return once the $coro terminates. |
413 | return once the $coro terminates. |
427 | |
414 | |
428 | $coro->on_destroy (\&cb) |
415 | $coro->on_destroy (\&cb) |
429 | Registers a callback that is called when this coro gets destroyed, |
416 | Registers a callback that is called when this coro thread gets |
430 | but before it is joined. The callback gets passed the terminate |
417 | destroyed, but before it is joined. The callback gets passed the |
431 | arguments, if any, and *must not* die, under any circumstances. |
418 | terminate arguments, if any, and *must not* die, under any |
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419 | circumstances. |
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420 | |
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421 | There can be any number of "on_destroy" callbacks per coro. |
432 | |
422 | |
433 | $oldprio = $coro->prio ($newprio) |
423 | $oldprio = $coro->prio ($newprio) |
434 | Sets (or gets, if the argument is missing) the priority of the coro. |
424 | Sets (or gets, if the argument is missing) the priority of the coro |
435 | Higher priority coro get run before lower priority coro. Priorities |
425 | thread. Higher priority coro get run before lower priority coros. |
436 | are small signed integers (currently -4 .. +3), that you can refer |
426 | Priorities are small signed integers (currently -4 .. +3), that you |
437 | to using PRIO_xxx constants (use the import tag :prio to get then): |
427 | can refer to using PRIO_xxx constants (use the import tag :prio to |
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428 | get then): |
438 | |
429 | |
439 | PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
430 | PRIO_MAX > PRIO_HIGH > PRIO_NORMAL > PRIO_LOW > PRIO_IDLE > PRIO_MIN |
440 | 3 > 1 > 0 > -1 > -3 > -4 |
431 | 3 > 1 > 0 > -1 > -3 > -4 |
441 | |
432 | |
442 | # set priority to HIGH |
433 | # set priority to HIGH |
443 | current->prio (PRIO_HIGH); |
434 | current->prio (PRIO_HIGH); |
444 | |
435 | |
445 | The idle coro ($Coro::idle) always has a lower priority than any |
436 | The idle coro thread ($Coro::idle) always has a lower priority than |
446 | existing coro. |
437 | any existing coro. |
447 | |
438 | |
448 | Changing the priority of the current coro will take effect |
439 | Changing the priority of the current coro will take effect |
449 | immediately, but changing the priority of coro in the ready queue |
440 | immediately, but changing the priority of a coro in the ready queue |
450 | (but not running) will only take effect after the next schedule (of |
441 | (but not running) will only take effect after the next schedule (of |
451 | that coro). This is a bug that will be fixed in some future version. |
442 | that coro). This is a bug that will be fixed in some future version. |
452 | |
443 | |
453 | $newprio = $coro->nice ($change) |
444 | $newprio = $coro->nice ($change) |
454 | Similar to "prio", but subtract the given value from the priority |
445 | Similar to "prio", but subtract the given value from the priority |
455 | (i.e. higher values mean lower priority, just as in unix). |
446 | (i.e. higher values mean lower priority, just as in UNIX's nice |
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447 | command). |
456 | |
448 | |
457 | $olddesc = $coro->desc ($newdesc) |
449 | $olddesc = $coro->desc ($newdesc) |
458 | Sets (or gets in case the argument is missing) the description for |
450 | Sets (or gets in case the argument is missing) the description for |
459 | this coro. This is just a free-form string you can associate with a |
451 | this coro thread. This is just a free-form string you can associate |
460 | coro. |
452 | with a coro. |
461 | |
453 | |
462 | This method simply sets the "$coro->{desc}" member to the given |
454 | This method simply sets the "$coro->{desc}" member to the given |
463 | string. You can modify this member directly if you wish. |
455 | string. You can modify this member directly if you wish, and in |
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456 | fact, this is often preferred to indicate major processing states |
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457 | that cna then be seen for example in a Coro::Debug session: |
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458 | |
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459 | sub my_long_function { |
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460 | local $Coro::current->{desc} = "now in my_long_function"; |
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461 | ... |
|
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462 | $Coro::current->{desc} = "my_long_function: phase 1"; |
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463 | ... |
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464 | $Coro::current->{desc} = "my_long_function: phase 2"; |
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465 | ... |
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466 | } |
464 | |
467 | |
465 | GLOBAL FUNCTIONS |
468 | GLOBAL FUNCTIONS |
466 | Coro::nready |
469 | Coro::nready |
467 | Returns the number of coro that are currently in the ready state, |
470 | Returns the number of coro that are currently in the ready state, |
468 | i.e. that can be switched to by calling "schedule" directory or |
471 | i.e. that can be switched to by calling "schedule" directory or |
… | |
… | |
485 | The reason this function exists is that many event libraries (such |
488 | The reason this function exists is that many event libraries (such |
486 | as the venerable Event module) are not thread-safe (a weaker form of |
489 | as the venerable Event module) are not thread-safe (a weaker form of |
487 | reentrancy). This means you must not block within event callbacks, |
490 | reentrancy). This means you must not block within event callbacks, |
488 | otherwise you might suffer from crashes or worse. The only event |
491 | otherwise you might suffer from crashes or worse. The only event |
489 | library currently known that is safe to use without "unblock_sub" is |
492 | library currently known that is safe to use without "unblock_sub" is |
490 | EV. |
493 | EV (but you might still run into deadlocks if all event loops are |
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494 | blocked). |
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495 | |
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496 | Coro will try to catch you when you block in the event loop |
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497 | ("FATAL:$Coro::IDLE blocked itself"), but this is just best effort |
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498 | and only works when you do not run your own event loop. |
491 | |
499 | |
492 | This function allows your callbacks to block by executing them in |
500 | This function allows your callbacks to block by executing them in |
493 | another coro where it is safe to block. One example where blocking |
501 | 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 |
502 | is handy is when you use the Coro::AIO functions to save results to |
495 | disk, for example. |
503 | disk, for example. |
… | |
… | |
506 | when you use a module that uses AnyEvent (and you use |
514 | when you use a module that uses AnyEvent (and you use |
507 | Coro::AnyEvent) and it provides callbacks that are the result of |
515 | Coro::AnyEvent) and it provides callbacks that are the result of |
508 | some event callback, then you must not block either, or use |
516 | some event callback, then you must not block either, or use |
509 | "unblock_sub". |
517 | "unblock_sub". |
510 | |
518 | |
511 | $cb = Coro::rouse_cb |
519 | $cb = rouse_cb |
512 | Create and return a "rouse callback". That's a code reference that, |
520 | Create and return a "rouse callback". That's a code reference that, |
513 | when called, will remember a copy of its arguments and notify the |
521 | when called, will remember a copy of its arguments and notify the |
514 | owner coro of the callback. |
522 | owner coro of the callback. |
515 | |
523 | |
516 | See the next function. |
524 | See the next function. |
517 | |
525 | |
518 | @args = Coro::rouse_wait [$cb] |
526 | @args = rouse_wait [$cb] |
519 | Wait for the specified rouse callback (or the last one that was |
527 | Wait for the specified rouse callback (or the last one that was |
520 | created in this coro). |
528 | created in this coro). |
521 | |
529 | |
522 | As soon as the callback is invoked (or when the callback was invoked |
530 | As soon as the callback is invoked (or when the callback was invoked |
523 | before "rouse_wait"), it will return the arguments originally passed |
531 | before "rouse_wait"), it will return the arguments originally passed |
524 | to the rouse callback. |
532 | to the rouse callback. In scalar context, that means you get the |
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533 | *last* argument, just as if "rouse_wait" had a "return ($a1, $a2, |
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534 | $a3...)" statement at the end. |
525 | |
535 | |
526 | See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
536 | See the section HOW TO WAIT FOR A CALLBACK for an actual usage |
527 | example. |
537 | example. |
528 | |
538 | |
529 | HOW TO WAIT FOR A CALLBACK |
539 | HOW TO WAIT FOR A CALLBACK |
… | |
… | |
606 | unix roughly halves perl performance, even when not used. |
616 | unix roughly halves perl performance, even when not used. |
607 | |
617 | |
608 | coro switching is not signal safe |
618 | coro switching is not signal safe |
609 | You must not switch to another coro from within a signal handler |
619 | You must not switch to another coro from within a signal handler |
610 | (only relevant with %SIG - most event libraries provide safe |
620 | (only relevant with %SIG - most event libraries provide safe |
611 | signals). |
621 | signals), *unless* you are sure you are not interrupting a Coro |
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622 | function. |
612 | |
623 | |
613 | That means you *MUST NOT* call any function that might "block" the |
624 | That means you *MUST NOT* call any function that might "block" the |
614 | current coro - "cede", "schedule" "Coro::Semaphore->down" or |
625 | current coro - "cede", "schedule" "Coro::Semaphore->down" or |
615 | anything that calls those. Everything else, including calling |
626 | anything that calls those. Everything else, including calling |
616 | "ready", works. |
627 | "ready", works. |
617 | |
628 | |
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629 | WINDOWS PROCESS EMULATION |
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630 | A great many people seem to be confused about ithreads (for example, |
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631 | Chip Salzenberg called me unintelligent, incapable, stupid and gullible, |
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632 | while in the same mail making rather confused statements about perl |
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633 | ithreads (for example, that memory or files would be shared), showing |
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634 | his lack of understanding of this area - if it is hard to understand for |
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635 | Chip, it is probably not obvious to everybody). |
|
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636 | |
|
|
637 | What follows is an ultra-condensed version of my talk about threads in |
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638 | scripting languages given on the perl workshop 2009: |
|
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639 | |
|
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640 | The so-called "ithreads" were originally implemented for two reasons: |
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641 | first, to (badly) emulate unix processes on native win32 perls, and |
|
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642 | secondly, to replace the older, real thread model ("5.005-threads"). |
|
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643 | |
|
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644 | It does that by using threads instead of OS processes. The difference |
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645 | between processes and threads is that threads share memory (and other |
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646 | state, such as files) between threads within a single process, while |
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647 | processes do not share anything (at least not semantically). That means |
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648 | that modifications done by one thread are seen by others, while |
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649 | modifications by one process are not seen by other processes. |
|
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650 | |
|
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651 | The "ithreads" work exactly like that: when creating a new ithreads |
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652 | process, all state is copied (memory is copied physically, files and |
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653 | code is copied logically). Afterwards, it isolates all modifications. On |
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654 | UNIX, the same behaviour can be achieved by using operating system |
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655 | processes, except that UNIX typically uses hardware built into the |
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656 | system to do this efficiently, while the windows process emulation |
|
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657 | emulates this hardware in software (rather efficiently, but of course it |
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658 | is still much slower than dedicated hardware). |
|
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659 | |
|
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660 | As mentioned before, loading code, modifying code, modifying data |
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661 | structures and so on is only visible in the ithreads process doing the |
|
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662 | modification, not in other ithread processes within the same OS process. |
|
|
663 | |
|
|
664 | This is why "ithreads" do not implement threads for perl at all, only |
|
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665 | processes. What makes it so bad is that on non-windows platforms, you |
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666 | can actually take advantage of custom hardware for this purpose (as |
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667 | evidenced by the forks module, which gives you the (i-) threads API, |
|
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668 | just much faster). |
|
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669 | |
|
|
670 | Sharing data is in the i-threads model is done by transfering data |
|
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671 | structures between threads using copying semantics, which is very slow - |
|
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672 | shared data simply does not exist. Benchmarks using i-threads which are |
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673 | communication-intensive show extremely bad behaviour with i-threads (in |
|
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674 | fact, so bad that Coro, which cannot take direct advantage of multiple |
|
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675 | CPUs, is often orders of magnitude faster because it shares data using |
|
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676 | real threads, refer to my talk for details). |
|
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677 | |
|
|
678 | As summary, i-threads *use* threads to implement processes, while the |
|
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679 | compatible forks module *uses* processes to emulate, uhm, processes. |
|
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680 | I-threads slow down every perl program when enabled, and outside of |
|
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681 | windows, serve no (or little) practical purpose, but disadvantages every |
|
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682 | single-threaded Perl program. |
|
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683 | |
|
|
684 | This is the reason that I try to avoid the name "ithreads", as it is |
|
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685 | misleading as it implies that it implements some kind of thread model |
|
|
686 | for perl, and prefer the name "windows process emulation", which |
|
|
687 | describes the actual use and behaviour of it much better. |
|
|
688 | |
618 | SEE ALSO |
689 | SEE ALSO |
619 | Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
690 | Event-Loop integration: Coro::AnyEvent, Coro::EV, Coro::Event. |
620 | |
691 | |
621 | Debugging: Coro::Debug. |
692 | Debugging: Coro::Debug. |
622 | |
693 | |