Multithreading

This is a discussion on Multithreading within the Windows Programming forums, part of the Platform Specific Boards category; Yesterday i built a little test program that created 10 threads, where in each i called a function which run ...

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    Programming Wraith GReaper's Avatar
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    Multithreading

    Yesterday i built a little test program that created 10 threads, where in each i called a function which run a quite big loop. After multiple testings i realised that when running each function in a different thread, and waiting for all of them to finish of course, that it would terminate at almost half the time as when running the function 10 times in the same process. How's that possible? I know it can be done in multiprocessor system, but mine is Intel Core 2 Duo ( Two cores but still one processor ). Am i missing something? Can multicored processor run faster when using multithreading?
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    It can, yes - additionally, it depends on what your function's doing. If it's making some system call that might block, it will be much more efficient to make it ten times concurrently than it will be to make it ten times consecutively. If the call is for blocking I/O, for example, where most of the time will be spent waiting for hardware to do whatever it's doing, this may well be the case.

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    Programming Wraith GReaper's Avatar
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    Ok, but can i say that those 10 thread, or some of them, run at exactly the same time?
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    Quote Originally Posted by Sipher View Post
    Ok, but can i say that those 10 thread, or some of them, run at exactly the same time?
    Up to two of them may do, on a dual-core processor, but that would be an accident and not generally something you'd care to know about. They only run "at the same time" in a conceptual sense - it's a useful way to think about them at a certain level of abstraction (e.g. when you want to make ten system calls concurrently), but in actual fact they probably won't literally run at the same time.

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    Unregistered User Yarin's Avatar
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    This may be a stupid question, but it has happened to me: Are you sure the function is thread safe? If it's not, the concurrency could mess it up, causing some threads' execution of the function to prematurely return.

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