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Further tweaked QRingBuffer for added sanity

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sergm
2020-09-06 10:04:10 +03:00
parent 3f2bdfcb8c
commit d40a7d2f61
1 changed files with 9 additions and 8 deletions
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17
mt32emu_qt/src/QRingBuffer.cpp
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@@ -69,7 +69,10 @@ QRingBuffer::~QRingBuffer() {
}
void *QRingBuffer::writePointer(quint32 &bytesFree, bool &freeSpaceContiguous) const {
quint32 myReadPosition = loadRelaxed(readPosition);
// Aquire barrier ensures that data is never written ahead of the indices, when the buffer
// space might still be in use. In practice however, this is barely possible, because all
// subsequent data writes depend on values of the indices, but shouldn't hurt anyway.
quint32 myReadPosition = loadAcquire(readPosition);
quint32 myWritePosition = loadRelaxed(writePosition);
bool wrapped = myWritePosition < myReadPosition;
bytesFree = (wrapped ? myReadPosition : bufferSize) - myWritePosition;
@@ -90,9 +93,9 @@ void QRingBuffer::advanceWritePointer(quint32 bytesWritten) {
}
void *QRingBuffer::readPointer(quint32 &bytesReady) const {
// Aquire barrier ensures that data is never read ahead of the indices.
// In practice, this should never be the case due to the implicit dependency,
// but shouldn't hurt anyway.
// Aquire barrier ensures that data is never read ahead of the indices, when the buffer
// space might not contain valid data yet. In practice however, this is barely possible,
// because all subsequent data reads depend on values of the indices, but shouldn't hurt anyway.
quint32 myReadPosition = loadRelaxed(readPosition);
quint32 myWritePosition = loadAcquire(writePosition);
bytesReady = (myWritePosition < myReadPosition ? bufferSize : myWritePosition) - myReadPosition;
@@ -100,13 +103,11 @@ void *QRingBuffer::readPointer(quint32 &bytesReady) const {
}
void QRingBuffer::advanceReadPointer(quint32 bytesRead) {
// Full barrier here prevents late data reads from possible overlapping with early writes.
// Using a combination of loadAcquire and storeRelease here to simulate it,
// since Qt API lacks operations for simple atomic load or store with the ordered semantic.
quint32 myReadPosition = loadAcquire(readPosition);
quint32 myReadPosition = loadRelaxed(readPosition);
myReadPosition += bytesRead;
if (bufferSize <= myReadPosition) {
myReadPosition -= bufferSize;
}
// Release barrier ensures that data is completely read prior to updating the index.
storeRelease(readPosition, myReadPosition);
}