Is is possible to create a semaphore accessable to both Windows and Qt applications?

  • I tried to create a named semaphore in a Windows application using following code:

    m_hSemaphore = ::CreateSemaphore(NULL, 0, 100, "semaphore_test");

    and in my Qt application I open a semaphore of the same name:

    pSemaphore = new QSystemSemaphore(tr("semaphore_test"), 0, QSystemSemaphore::Open);

    But when the semaphore is released in Windows application, in Qt application,


    is still blocked, which means two applications are not accessing the samesemaphore.

    Is there a way to make both applications access the same semaphore? The similar problem also exists in accessing shared memory in both Windows and Qt applications.

  • AFAIK Qt will decorate the Semaphore name, when using QSystemSemaphore().

    You can use a tool such as ProcessExplorer to lookup the actual (native) name of the Semaphore...

    ! from ProcessExplorer)!

    Looks like the string "qipc_systemsem_" followed by a hash of the specified string is used ;-)

  • bq. Thank you very much for your help! Now I can make Windows application and Qt application use a same semaphore.
    ProcessExplorer does not show shared memory used by a process, so making Windows application and Qt application use same shared memory is still a problem. Any ideas?

    The "shared" memory is nothing but a "memory mapped file", one that is backed by the system page file rather than by a file system file. Doesn't it show up under the file handles in ProcessExplorer?

  • No, it does not show up.

  • I'm now at home and just check it. It does show up! But as a "section", not as a "file" ;-)


  • I see, thanks! By the way, I just noticed that QSharedMemory::setNativeKey will set the native, platform specific key for this shared memory object, that will also help in Qt code to connect to shared memory created from Windows code.

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