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Re^3: OT: Locking and syncing mechanisms available on *nix.

by nikosv (Hermit)
on Mar 27, 2011 at 11:34 UTC ( #895744=note: print w/ replies, xml ) Need Help??


in reply to Re^2: OT: Locking and syncing mechanisms available on *nix.
in thread OT: Locking and syncing mechanisms available on *nix.

Also, I'm not sure what use the second link was?

It's what is behind the BackgroundWorker component.

I've posted it here just for informational purposes,looking at an alternative concept-wise,since it is releated to windows and threading


Comment on Re^3: OT: Locking and syncing mechanisms available on *nix.
Re^4: OT: Locking and syncing mechanisms available on *nix.
by BrowserUk (Pope) on Mar 27, 2011 at 12:22 UTC

    Ah. Okay. I don't use, nor have any time for the O'Woe dodo that is .NET, so that's of no use to me.

    What I'm really looking for (I think) is a *nix equivalent to Windows Event Objects. Basically, a non-polling, non-spinning mechanism to have one thread block until another thread signals.

    In theory, pthread condition variables ought to be usable for this. In practice, using a condition variable also requires the use of a mutex, which I don't need or want. I'm not trying to mutually exclude anything. Nor do I see a convenient place to put a mutex that I don't need.

    I've run across a few mentions of something called a "futex" which is compared to Window's Event objects, but looking that term up it is defined as a 'fast user mutex'. Again, I'm not trying to mutually exclude anything!

    The situation I'm trying to deal with would seem to be a relatively common occurrence. This thread has detected a situation that means it cannot proceed until some other thread does something. It therefore need to block until that other thread signals that it has been done. So, it reset an event and waits for it to be signalled. The other thread signals that event each time it does whatever it is required to do to allow the first thread to move forward.

    But I don't see how to do this with *nix?


    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    "Science is about questioning the status quo. Questioning authority".
    In the absence of evidence, opinion is indistinguishable from prejudice.
      pthread.h: barriers
      semaphore.h: semaphores
      ipc.h + sem.h: ipc v semaphores
      ipc.h + msg.h: ipc v message queues
      Events can be achieved with a combination of conditional variables and a mutex. Check pthread_cond_timedwait()(search for it inside the page)

        I know, but as I don't have anything I want to mutually exclude access to, I don't want to use the (by all accounts very expensive) mutex mechanism.


        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
      I'm not trying to mutually exclude anything.
      You actually need to mutually exclude access to the condition variable. I don't use Perl threads much, but it looks like threads::shared has the necessary ingredients, and you can do something like this:
      my $cond : shared; $thread1 = async { { lock($cond); cond_wait($cond) until $cond } # do stuff. }; $thread2 = async { # do stuff. { lock($cond); $cond = "proceed"; cond_signal($cond) } };

        Sorry, I guess I should have mentioned I'm operating in XS with no access to threads::shared. Indeed, I'm specifically trying to replace it.


        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.

      Ah. Okay. I don't use, nor have any time for the O’Woe dodo that is .NET.   So that’s no use to me.

      I like that!!   My sentiments exactly!   :-D

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