Windows Audio / WaveInAddBuffer() blocks

Question

My application records audio samples from a microphone connected to my PC. So I chose the Windows WaveInXXX API to do the job.

After reading the documentation I decided to avoid using the callback mechanism with WaveInProc to save me the hassle synchronizing the threads. The whole application is pretty big and I thought this would make debugging simpler. When the application requests a block of samples, I just iterate over my buffer queue, take one out, copy the data, unprepare it, prepare it and add it back to the buffer queue. Basic program structure looks like this, I hope it makes the basic program flow clear:

WaveInOpen()
WaveInStart()
FunctionAddingPreparedBuffersToTheQueue()
while(someConditionThatEventuallyBecomesFalse)
    if(NextBufferInQueueIsMarkedDone)
        GetDataFromBuffer()
        UnpreparePrepareHeaderAndAddBuffer()
    else
        WaitForAShortTime()
WaveInStop()
WaveInClose()

Now the problem appears: After some time (and I am unable to reproduce the exact condition), WaveInAddBuffer() causes a deadlock although it's in the same thread as all the rest. The header for the buffer that shall be added when the deadlock happens is prepared and dwFlags == WHDR_PREPARED == 2.

Any ideas what could cause this deadlock?

Answer 1

I have not seen such a problem, but a guess might be something like fragmentation related to all the unprepare/prepare cycles. They are not necessary. You can do the prepare once for each buffer and then unprepare when finished recording. (Prepare locks the buffer into physical memory.)