QIODevice: make the read/write chunk sizes configurable

By default, the read chunk size is QIODEVICE_BUFFERSIZE and the write
chunk size is 0 (which means that we don't use the internal write buffer).
Derived classes may override these values to define the size of
QIODevice's write buffer or to optimize the read buffer use.

Bump the TypeInformationVersion field in qtHookData, to notify the
Qt Creator developers that the offset of QFilePrivate::fileName was
changed and dumpers should be adapted.

Change-Id: Ib732bc94be8da8a5514a6e5dcc04445895f130d8
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

src/corelib/global/qhooks.cpp

@@ -67,7 +67,7 @@ quintptr Q_CORE_EXPORT qtHookData[] = {
     // The required sizes and offsets are tested in tests/auto/other/toolsupport.
     // When this fails and the change was intentional, adjust the test and
     // adjust this value here.
-    2
+    3
 };
 
 Q_STATIC_ASSERT(QHooks::LastHookIndex == sizeof(qtHookData) / sizeof(qtHookData[0]));

src/corelib/io/qiodevice.cpp

@@ -154,6 +154,8 @@ QIODevicePrivate::QIODevicePrivate()
       writeChannelCount(0),
       currentReadChannel(0),
       currentWriteChannel(0),
+      readBufferChunkSize(QIODEVICE_BUFFERSIZE),
+      writeBufferChunkSize(0),
       transactionPos(0),
       transactionStarted(false)
        , baseReadLineDataCalled(false)
@@ -675,7 +677,7 @@ void QIODevicePrivate::setReadChannelCount(int count)
 {
     if (count > readBuffers.size()) {
         readBuffers.insert(readBuffers.end(), count - readBuffers.size(),
-                           QRingBuffer(QIODEVICE_BUFFERSIZE));
+                           QRingBuffer(readBufferChunkSize));
     } else {
         readBuffers.resize(count);
     }
@@ -723,8 +725,12 @@ void QIODevice::setCurrentWriteChannel(int channel)
 void QIODevicePrivate::setWriteChannelCount(int count)
 {
     if (count > writeBuffers.size()) {
-        writeBuffers.insert(writeBuffers.end(), count - writeBuffers.size(),
-                            QRingBuffer(QIODEVICE_BUFFERSIZE));
+        // If writeBufferChunkSize is zero (default value), we don't use
+        // QIODevice's write buffers.
+        if (writeBufferChunkSize != 0) {
+            writeBuffers.insert(writeBuffers.end(), count - writeBuffers.size(),
+                                QRingBuffer(writeBufferChunkSize));
+        }
     } else {
         writeBuffers.resize(count);
     }
@@ -1035,7 +1041,7 @@ qint64 QIODevice::read(char *data, qint64 maxSize)
             // Make sure the device is positioned correctly.
             if (sequential || d->pos == d->devicePos || seek(d->pos)) {
                 madeBufferReadsOnly = false; // fix readData attempt
-                if ((maxSize >= QIODEVICE_BUFFERSIZE || (d->openMode & Unbuffered))
+                if ((maxSize >= d->readBufferChunkSize || (d->openMode & Unbuffered))
                     && !keepDataInBuffer) {
                     // Read big chunk directly to output buffer
                     readFromDevice = readData(data, maxSize);
@@ -1056,7 +1062,8 @@ qint64 QIODevice::read(char *data, qint64 maxSize)
                 } else {
                     // Do not read more than maxSize on unbuffered devices
                     const qint64 bytesToBuffer = (d->openMode & Unbuffered)
-                            ? qMin(maxSize, QIODEVICE_BUFFERSIZE) : QIODEVICE_BUFFERSIZE;
+                            ? qMin(maxSize, qint64(d->readBufferChunkSize))
+                            : qint64(d->readBufferChunkSize);
                     // Try to fill QIODevice buffer by single read
                     readFromDevice = readData(d->buffer.reserve(bytesToBuffer), bytesToBuffer);
                     deviceAtEof = (readFromDevice != bytesToBuffer);
@@ -1146,8 +1153,6 @@ QByteArray QIODevice::read(qint64 maxSize)
 #if defined QIODEVICE_DEBUG
     printf("%p QIODevice::read(%lld), d->pos = %lld, d->buffer.size() = %lld\n",
            this, maxSize, d->pos, d->buffer.size());
-#else
-    Q_UNUSED(d);
 #endif
 
     if (maxSize >= MaxByteArraySize) {
@@ -1162,11 +1167,11 @@ QByteArray QIODevice::read(qint64 maxSize)
             // If resize fails, read incrementally.
             qint64 readResult;
             do {
-                result.resize(int(qMin(maxSize, result.size() + QIODEVICE_BUFFERSIZE)));
+                result.resize(int(qMin(maxSize, qint64(result.size() + d->readBufferChunkSize))));
                 readResult = read(result.data() + readBytes, result.size() - readBytes);
                 if (readResult > 0 || readBytes == 0)
                     readBytes += readResult;
-            } while (readResult == QIODEVICE_BUFFERSIZE);
+            } while (readResult == d->readBufferChunkSize);
         } else {
             readBytes = read(result.data(), result.size());
         }
@@ -1202,7 +1207,7 @@ QByteArray QIODevice::readAll()
     qint64 readBytes = (d->isSequential() ? Q_INT64_C(0) : size());
     if (readBytes == 0) {
         // Size is unknown, read incrementally.
-        qint64 readChunkSize = qMax(QIODEVICE_BUFFERSIZE,
+        qint64 readChunkSize = qMax(qint64(d->readBufferChunkSize),
                                     d->isSequential() ? (d->buffer.size() - d->transactionPos)
                                                       : d->buffer.size());
         qint64 readResult;
@@ -1215,7 +1220,7 @@ QByteArray QIODevice::readAll()
             readResult = read(result.data() + readBytes, readChunkSize);
             if (readResult > 0 || readBytes == 0) {
                 readBytes += readResult;
-                readChunkSize = QIODEVICE_BUFFERSIZE;
+                readChunkSize = d->readBufferChunkSize;
             }
         } while (readResult > 0);
     } else {
@@ -1394,8 +1399,6 @@ QByteArray QIODevice::readLine(qint64 maxSize)
 #if defined QIODEVICE_DEBUG
     printf("%p QIODevice::readLine(%lld), d->pos = %lld, d->buffer.size() = %lld\n",
            this, maxSize, d->pos, d->buffer.size());
-#else
-    Q_UNUSED(d);
 #endif
 
     if (maxSize >= MaxByteArraySize) {
@@ -1415,11 +1418,11 @@ QByteArray QIODevice::readLine(qint64 maxSize)
 
         qint64 readResult;
         do {
-            result.resize(int(qMin(maxSize, result.size() + QIODEVICE_BUFFERSIZE)));
+            result.resize(int(qMin(maxSize, qint64(result.size() + d->readBufferChunkSize))));
             readResult = readLine(result.data() + readBytes, result.size() - readBytes);
             if (readResult > 0 || readBytes == 0)
                 readBytes += readResult;
-        } while (readResult == QIODEVICE_BUFFERSIZE
+        } while (readResult == d->readBufferChunkSize
                 && result[int(readBytes - 1)] != '\n');
     } else
         readBytes = readLine(result.data(), result.size());

src/corelib/io/qiodevice_p.h

@@ -64,7 +64,7 @@
 QT_BEGIN_NAMESPACE
 
 #ifndef QIODEVICE_BUFFERSIZE
-#define QIODEVICE_BUFFERSIZE Q_INT64_C(16384)
+#define QIODEVICE_BUFFERSIZE 16384
 #endif
 
 Q_CORE_EXPORT int qt_subtract_from_timeout(int timeout, int elapsed);
@@ -125,6 +125,8 @@ public:
     int writeChannelCount;
     int currentReadChannel;
     int currentWriteChannel;
+    int readBufferChunkSize;
+    int writeBufferChunkSize;
     qint64 transactionPos;
     bool transactionStarted;
     bool baseReadLineDataCalled;

tests/auto/other/toolsupport/tst_toolsupport.cpp

@@ -124,7 +124,7 @@ void tst_toolsupport::offsets_data()
     {
         QTestData &data = QTest::newRow("QFilePrivate::fileName")
                 << pmm_to_offsetof(&QFilePrivate::fileName);
-        data << 188 << 272;
+        data << 196 << 280;
     }
 #endif