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QIODevice: allow zero-copy in read()

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Try to prevent the data from being copied, if we have a chunk with the
same size in the read buffer.

Task-number: QTBUG-19169
Change-Id: I2a9a5c88855988888b56d0ca69ec4e50b8e6ef98
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>
This commit is contained in:
Alex Trotsenko 2016-02-19 16:52:29 +02:00
parent d1b09dba45
commit 5dc13fe05e
1 changed files with 13 additions and 2 deletions
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15
src/corelib/io/qiodevice.cpp
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@ -1148,13 +1148,24 @@ QByteArray QIODevice::read(qint64 maxSize)
Q_D(QIODevice);
QByteArray result;
CHECK_MAXLEN(read, result);
#if defined QIODEVICE_DEBUG
printf("%p QIODevice::read(%lld), d->pos = %lld, d->buffer.size() = %lld\n",
this, maxSize, d->pos, d->buffer.size());
#endif
// Try to prevent the data from being copied, if we have a chunk
// with the same size in the read buffer.
if (maxSize == d->buffer.nextDataBlockSize() && !d->transactionStarted
&& (d->openMode & (QIODevice::ReadOnly | QIODevice::Text)) == QIODevice::ReadOnly) {
result = d->buffer.read();
if (!d->isSequential())
d->pos += maxSize;
if (d->buffer.isEmpty())
readData(nullptr, 0);
return result;
}
CHECK_MAXLEN(read, result);
if (maxSize >= MaxByteArraySize) {
checkWarnMessage(this, "read", "maxSize argument exceeds QByteArray size limit");
maxSize = MaxByteArraySize - 1;