in reply to Re^6: need a thread to wait until a buffer is full.
in thread need a thread to wait until a buffer is full.

I thought signals and threads were an iffy combination? Meaning that the main thread tends to intercept all signals? So what if you wanted 2 or 3 buffers? A shared variable can be buffer specific, whereas a signal may be non-specific. (I may have mistakenly used the word "signal" in my node above, in a generic manner, where I really meant "set a shared variable which would signal......."
I'm not really a human, but I play one on earth. Cogito ergo sum a bum
  • Comment on Re^7: need a thread to wait until a buffer is full.

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Re^8: need a thread to wait until a buffer is full.
by BrowserUk (Patriarch) on Jul 25, 2007 at 17:46 UTC

    They aren't signals in that sense of the word. In the sense of cond_signal().

    Basically, the thread in waiting on cond_wait() will not be allocated any timeslices by the scheduler until the other thread calls cond_signal() (or broadcast). So, no polling a second shared var to see if the first is ready yet.

    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".
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      I'll have to look into that, but if the thread waits (without any timeslices) for the cond_signal from the other thread, that would limit it to watching only 1 thread. The way I envisioned it, the controlling thread could ask many other threads to fill their buffers simultaneously, and then go into a loop to harvest them as they come in, and still do other things as well, like asking for more buffer-filling.
      I'm not really a human, but I play one on earth. Cogito ergo sum a bum
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        but if the thread waits (without any timeslices) for the cond_signal from the other thread, that would limit it to watching only 1 thread.

        No, that is not so. The variable upon which the cond_wait() is waiting can be cond_signal()ed from any thread (that has a lock on the variable).

        Also, if more than one thread are in a cond_wait() state on the same variable, one of them (non-determanistically) will be awoken.

        You can also signal a variable using cond_broadcast(), in which case all threads currently blocking on that variable will be woken up, rather than just one.

        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.
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