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Thread: Create new QsharedMemory after crash

  1. #1
    Join Date
    Mar 2010
    Qt products
    Unix/X11 Windows

    Default Create new QsharedMemory after crash

    If application owning the QSharedMemory crashes, it will not detach so next time create will fail.
    From the document:
    QSharedMemory "owns" the shared memory segment. When the last thread or process that has an instance of QSharedMemory attached to a particular shared memory segment detaches from the segment by destroying its instance of QSharedMemory, the Unix kernel release the shared memory segment. But if that last thread or process crashes without running the QSharedMemory destructor, the shared memory segment survives the crash.

    My question is this: before I call create, if I try to atatch and detach will it detect that this is the last process and thus release the segment? If not, is there any Qt way to release the shared memory without using ipcrm?

    Here is a possible code snippet:

    Qt Code:
    1. QSharedMemory * hnd = NULL;
    2. QSharedMemory * pHnd = new QSharedMemory(strKey);
    3. if (pHnd)
    4. {
    5. // Try to attach and detach to handle crashed segments
    6. if (pHnd->attach(QSharedMemory::ReadOnly))
    7. pHnd->detach();
    8. // Now create brand new segment
    9. if (pHnd->create(size))
    10. hnd = pHnd;
    11. else
    12. delete pHnd;
    13. }
    14. return hnd; // Null if unsuccessful
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    Last edited by dashesy; 30th June 2012 at 01:25.

  2. #2
    Join Date
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    Warsaw, Poland
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    Qt products
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    Default Re: Create new QsharedMemory after crash

    Why don't you just try and see?
    Your biological and technological distinctiveness will be added to our own. Resistance is futile.

    Please ask Qt related questions on the forum and not using private messages or visitor messages.

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