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NAME |
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Coro::Multicore - make coro threads on multiple cores with specially |
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supported modules |
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|
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SYNOPSIS |
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use Coro::Multicore; |
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|
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# or, if you want it disabled by default (e.g. to use it from a module) |
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use Coro::Multicore (); |
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|
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DESCRIPTION |
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EXPERIMENTAL WARNING: This module is in its early stages of development. |
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It's fine to try out, but it didn't receive the normal amount of testing |
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and real-world usage that my other modules have gone through. |
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|
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While Coro threads (unlike ithreads) provide real threads similar to |
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pthreads, python threads and so on, they do not run in parallel to each |
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other even on machines with multiple CPUs or multiple CPU cores. |
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|
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This module lifts this restriction under two very specific but useful |
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conditions: firstly, the coro thread executes in XS code and does not |
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touch any perl data structures, and secondly, the XS code is specially |
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prepared to allow this. |
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|
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This means that, when you call an XS function of a module prepared for |
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it, this XS function can execute in parallel to any other Coro threads. |
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|
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The mechanism to support this is easily added to existing modules and is |
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independent of Coro or Coro::Multicore, and therefore could be used, |
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without changes, with other, similar, modules, or even the perl core, |
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should it gain real thread support anytime soon. See |
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<http://perlmulticore.schmorp.de/> for more info on how to prepare a |
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module to allow parallel execution. Preparing an existing module is |
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easy, doesn't add much overhead and no dependencies. |
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|
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This module is an AnyEvent user (and also, if not obvious, uses Coro). |
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|
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HOW TO USE IT |
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It could hardly be simpler - if you use coro threads, and before you |
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call a supported lengthy operation implemented in XS, use this module |
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and other coro threads can run in parallel: |
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|
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use Coro::Multicore; |
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|
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This module has no important API functions to learn or remember. All you |
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need to do is *load* it before you can take advantage of it. |
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|
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EXPORTS |
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This module does not (at the moment) export any symbols. It does, |
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however, export "behaviour" - if you use the default import, then |
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Coro::Multicore will be enabled for all threads and all callers in the |
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whole program: |
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|
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use Coro::Multicore; |
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|
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In a module where you don't control what else might be loaded and run, |
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you might want to be more conservative, and not import anything. This |
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has the effect of not enabling the functionality by default, so you have |
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to enable it per scope: |
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|
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use Coro::Multicore (); |
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|
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sub myfunc { |
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Coro::Multicore::scoped_enable; |
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|
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# from here to the end of this function, and in any functions |
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# called from this function, tasks will be executed asynchronously. |
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} |
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|
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API FUNCTIONS |
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$previous = Coro::Multicore::enable [$enable] |
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This function enables (if $enable is true) or disables (if $enable |
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is false) the multicore functionality globally. By default, it is |
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enabled. |
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|
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This can be used to effectively disable this module's functionality |
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by default, and enable it only for selected threads or scopes, by |
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calling "Coro::Multicore::scope_enable". |
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|
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The function returns the previous value of the enable flag. |
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|
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Coro::Multicore::scoped_enable |
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This function instructs Coro::Multicore to handle all requests |
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executed in the current coro thread, from the call to the end of the |
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current scope. |
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|
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Calls to "scoped_enable" and "scoped_disable" don't nest very well |
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at the moment, so don't nest them. |
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|
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Coro::Multicore::scoped_disable |
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The opposite of "Coro::Multicore::scope_disable": instructs |
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Coro::Multicore to *not* handle the next multicore-enabled request. |
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|
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INTERACTION WITH OTHER SOFTWARE |
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This module is very similar to other environments where perl |
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interpreters are moved between threads, such as mod_perl2, and the same |
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caveats apply. |
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|
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I want to spell out the most important ones: |
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|
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pthreads usage |
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Any creation of pthreads make it impossible to fork portably from a |
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perl program, as forking from within a threaded program will leave |
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the program in a state similar to a signal handler. While it might |
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work on some platforms (as an extension), this might also result in |
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silent data corruption. It also seems to work most of the time, so |
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it's hard to test for this. |
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|
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I recommend using something like AnyEvent::Fork, which can create |
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subprocesses safely (via Proc::FastSpawn). |
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|
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Similar issues exist for signal handlers, although this module works |
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hard to keep safe perl signals safe. |
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|
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module support |
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This module moves the same perl interpreter between different |
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threads. Some modules might get confused by that (although this can |
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usually be considered a bug). This is a rare case though. |
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|
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event loop reliance |
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To be able to wake up programs waiting for results, this module |
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relies on an active event loop (via AnyEvent). This is used to |
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notify the perl interpreter when the asynchronous task is done. |
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|
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Since event loops typically fail to work properly after a fork, this |
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means that some operations that were formerly working will now hang |
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after fork. |
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|
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A workaround is to call "Coro::Multicore::enable 0" after a fork to |
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disable the module. |
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|
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Future versions of this module might do this automatically. |
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|
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BUGS |
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(OS-) threads are never released |
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At the moment, threads that were created once will never be freed. |
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They will be reused for asynchronous requests, though, so a slong as |
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you limit the maximum number of concurrent asynchronous tasks, this |
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will also limit the maximum number of threads created. |
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|
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Future versions will likely lift this limitation. |
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|
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AnyEvent is initalised at module load time |
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AnyEvent is initialised on module load, as opposed to at a later |
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time. |
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|
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Future versions will likely change this. |
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|
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AUTHOR |
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Marc Lehmann <schmorp@schmorp.de> |
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http://software.schmorp.de/pkg/AnyEvent-XSThreadPool.html |
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|
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Additional thanks to Zsbán Ambrus, who gave considerable desing input |
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for this module and the perl multicore specification. |
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