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Re^2: PerlIO file handle dup

by chris212 (Scribe)
on Mar 07, 2017 at 14:55 UTC ( #1183835=note: print w/replies, xml ) Need Help??


in reply to Re: PerlIO file handle dup
in thread PerlIO file handle dup

I'm not sure I tried passing data between threads with a shared array, but I think performance would be similar to a queue, which was too slow.

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Re^3: PerlIO file handle dup
by BrowserUk (Pope) on Mar 07, 2017 at 16:39 UTC
    but I think performance would be similar to a queue,

    The problem with a queue is that all locking is applied to the entire shared array, thus every lock blocks all contenders, even if they are after different elements of the array.

    If you look carefully at my example, you'll see that the @buffers array itself isn't (explicitly) shared and is never locked; only the per-thread scalar elements are.

    And as only the reader thread and 1 worker thread per buffer are competing for any given lock, all workers threads are free to continue independantly of each other.

    And finally, the lock on any given buffer is only held for the brief time it takes to copy its contents to a local buffer, thus the reader thread can be repopulating it with the next record whilst the worker thread is processing the previous one.

    The upshot is that in my use of this technique, it beats Thread::Queue by a wide margin for applications where the processing of a record takes 3x or more time, than that required to read it.

    Test it. You might be pleasantly surprised.


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