The problem seemed to be that I was using QByteArray's ::fromRawData on the pointer returned by the shared memory segment. When I copied that data explicitly using memcpy on this pointer, and then constructed my QByteArray using the copied data, then the seg faults stopped.
Qt QSharedMemory Segmentation Faults after Several Successful Writes
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24-03-2022 - |
Pregunta
I'm using QSharedMemory to store some data and want to subsequently append data to what is contained there. So I call the following code several times with new data. The "audioBuffer" is new data given to this function. I can call this function about 4-7 times ( and it varies ) before it seg faults on the memcpy operation. The size of the QSharedMemory location is huge so in the few calls that I do before seg faulting, there is no issue of memcpy copying data beyond it's boundaries. Also, m_SharedAudioBuffer.errorString() gives no errors up to the memcpy operation. Currently, I only have one process using this QSharedMemory segment. I also tried to write continually without appending each time and that works fine, so something is happening when I try to append more data to the shared memory segment. Any ideas? Thanks!
// Get the buffer size for the current audio buffer in shared memory
int bufferAudioDataSizeBytes = readFromSharedAudioBufferSizeMemory(); // This in number of bytes
// Create a bytearray with our data currently in the shared buffer
char* bufferAudioData = readFromSharedAudioBufferMemory();
QByteArray currentAudioStream = QByteArray::fromRawData(bufferAudioData,bufferAudioDataSizeBytes);
QByteArray currentAudioStreamDeepCopy(currentAudioStream);
currentAudioStreamDeepCopy.append(audioBuffer);
dataSize = currentAudioStreamDeepCopy.size();
//#if DEBUG
qDebug() << "Inserting audio buffer, new size is: " << dataSize;
//#endif
writeToSharedAudioBufferSizeMemory( dataSize ); // Just the size of what we received
// Write into the shared memory
m_SharedAudioBuffer.lock();
// Clear the buffer and define the copy locations
memset(m_SharedAudioBuffer.data(), '\0', m_SharedAudioBuffer.size());
char *to = (char*)m_SharedAudioBuffer.data();
char *from = (char*)audioBuffer.data();
// Now perform the actual copy operation to store the buffer
memcpy( to, from, dataSize );
// Release the lock
m_SharedAudioBuffer.unlock();
EDIT: Perhaps, this is due to my target embedded device which is very small. The available RAM is large when I am trying to write to shared memory, but I notice that in the /tmp directory ( which is only given 4Mb ) I have the following entries - the size is not nearly consumed in /tmp though so I'm not sure why I couldn't allocate more memory, also the QSharedMemory::create method never fails for my maximum size of 960000:
# cd /tmp/
# ls
QtSettings
lib
qipc_sharedmemory_AudioBufferData2a7d5f1a29e3d27dac65b4f350d76a0dfd442222
qipc_sharedmemory_AudioBufferSizeData6b7acc119f94322a6794cbca37ed63df07b733ab
qipc_systemsem_AudioBufferData2a7d5f1a29e3d27dac65b4f350d76a0dfd442222
qipc_systemsem_AudioBufferSizeData6b7acc119f94322a6794cbca37ed63df07b733ab
qtembedded-0
run
Solución