multithreaded reeading and writing from buffer

This is a discussion on multithreaded reeading and writing from buffer within the C++ Programming forums, part of the General Programming Boards category; The last years, 99% of my time I'm doing java so my C++ skills are well, erm, lets's say a ...

  1. #1
    Banned maes's Avatar
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    multithreaded reeading and writing from buffer

    The last years, 99% of my time I'm doing java so my C++ skills are well, erm, lets's say a bit at a low level.
    But I'm having a bit of a problem.
    I have a buffer that is accessed by two threads.
    One for reading and one for writing to the buffer (a vector).
    I'm pretty sure that I never write outside the memory allocated by the buffer.
    Due to performance issues we tryed removing 2 mutex locks and that worked CPU usage droped with 50%. We made the methods where we removed the mutex locks a bit smarter so we first check if we can safely read or not.
    That code isn't 100% safe because things can still go wrong between the check and the actual read.

    Now, about 2 or 3 times a day, we get a blue screen on Win XP and immediately after a reset of windows.
    Can this be the result of a push and pop on the same address?
    As far as I know, if I try to write beyond my allocated memory I would get an access violation message but windows wouldn't reset. Is this the same with reading and writing to the same address?

    I analysed the mini dumps from windows but that didn't give me any usefull information.

    I haven't been able to simulate it on the development machine with debuging capabilities nor am I allowed post any code.
    I also ran it with the ntsd but it hasn't crashed yet.

    Could the windows crash be related to our program or can it be a hardware fault (like a heat problem)?


    Thanks

    Maes
    Last edited by maes; 08-20-2007 at 01:39 AM.

  2. #2
    Deathray Engineer MacGyver's Avatar
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    I doubt you're causing the blue screen with that program unless your code is part of a driver (in which case unsafe thread code is a really baaaaaaaaad idea), or something else of that nature.

    Windows NT based systems, such as XP, are pretty stable and don't usually blue screen unless there is a driver problem or something hardware related.

  3. #3
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    I agree, it's very unlikely that you will crash the system with a user-mode application (unless you are talking to a borken driver of course).

    What is the bluescreen error you get?

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  4. #4
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by maes View Post
    Could the windows crash be related to our program or can it be a hardware fault (like a heat problem)?
    Unlikely, since the problem only appeared once you changed your code. You might spend all week speculating why Windows crashes, but that's probably not a good use of your time since you might find another box where it doesn't crash. Just fix the code and chalk it up to "Who knows with Windows."

  5. #5
    Banned maes's Avatar
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    Quote Originally Posted by matsp View Post
    I agree, it's very unlikely that you will crash the system with a user-mode application (unless you are talking to a borken driver of course).

    What is the bluescreen error you get?

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    Mats

    The blue screen disapears to quickly the computer resets immediatly after.
    But I think you're all right. Last night I had the original program running and it still did a reboot.
    So I doubt it will be a bug in our program.

    Thanks for the help,

    Maes

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    if i do not remember wrong you can download the tweakui utility from microsoft and disable the immediate reboot with it. then you are able to read the blue screen message.

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    Quote Originally Posted by pheres View Post
    if i do not remember wrong you can download the tweakui utility from microsoft and disable the immediate reboot with it. then you are able to read the blue screen message.
    Yes - in fact, it doesn't take a TweakUI either - just go to Control-Panel->System->Advanced and unclick "Automatically reboot" - or if you have a minidump, you should be able to see the fault that caused the dump.

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