QRingBuffer: add packet mode

As a special case, setting the value of chunk size to zero forces
QRingBuffer to produce a separate QByteArray on each call which
appends the data. So, this enables a packet mode where portions of
data are stored independently from each other.

Change-Id: I2d0b331211901a289da7d4533e974f06830b5590
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 44 insertions, 22 deletions

diff --git a/src/corelib/tools/qringbuffer.cpp b/src/corelib/tools/qringbuffer.cpp
index 4a2dfdec2b..cb11e72435 100644
--- a/src/corelib/tools/qringbuffer.cpp
+++ b/src/corelib/tools/qringbuffer.cpp
@@ -108,24 +108,25 @@ char *QRingBuffer::reserve(qint64 bytes)
     if (bytes <= 0 || bytes >= MaxByteArraySize)
         return 0;
 
-    if (buffers.isEmpty()) {
-        buffers.append(QByteArray());
-        buffers.first().resize(qMax(basicBlockSize, int(bytes)));
+    if (bufferSize == 0) {
+        if (buffers.isEmpty())
+            buffers.append(QByteArray(qMax(basicBlockSize, int(bytes)), Qt::Uninitialized));
+        else
+            buffers.first().resize(qMax(basicBlockSize, int(bytes)));
     } else {
         const qint64 newSize = bytes + tail;
-        // if need buffer reallocation
-        if (newSize > buffers.constLast().size()) {
-            if (newSize > buffers.constLast().capacity() && (tail >= basicBlockSize
-                    || newSize >= MaxByteArraySize)) {
-                // shrink this buffer to its current size
-                buffers.last().resize(tail);
-
-                // create a new QByteArray
-                buffers.append(QByteArray());
-                ++tailBuffer;
-                tail = 0;
-            }
-            buffers.last().resize(qMax(basicBlockSize, tail + int(bytes)));
+        // if need a new buffer
+        if (basicBlockSize == 0 || (newSize > buffers.constLast().capacity()
+                                    && (tail >= basicBlockSize || newSize >= MaxByteArraySize))) {
+            // shrink this buffer to its current size
+            buffers.last().resize(tail);
+
+            // create a new QByteArray
+            buffers.append(QByteArray(qMax(basicBlockSize, int(bytes)), Qt::Uninitialized));
+            ++tailBuffer;
+            tail = 0;
+        } else if (newSize > buffers.constLast().size()) {
+            buffers.last().resize(qMax(basicBlockSize, int(newSize)));
         }
     }
 
@@ -146,10 +147,8 @@ char *QRingBuffer::reserveFront(qint64 bytes)
     if (bytes <= 0 || bytes >= MaxByteArraySize)
         return 0;
 
-    if (head < bytes) {
-        if (buffers.isEmpty()) {
-            buffers.append(QByteArray());
-        } else {
+    if (head < bytes || basicBlockSize == 0) {
+        if (head > 0) {
             buffers.first().remove(0, head);
             if (tailBuffer == 0)
                 tail -= head;
@@ -157,12 +156,15 @@ char *QRingBuffer::reserveFront(qint64 bytes)
 
         head = qMax(basicBlockSize, int(bytes));
         if (bufferSize == 0) {
+            if (buffers.isEmpty())
+                buffers.prepend(QByteArray(head, Qt::Uninitialized));
+            else
+                buffers.first().resize(head);
             tail = head;
         } else {
-            buffers.prepend(QByteArray());
+            buffers.prepend(QByteArray(head, Qt::Uninitialized));
             ++tailBuffer;
         }
-        buffers.first().resize(head);
     }
 
     head -= int(bytes);
diff --git a/tests/auto/corelib/tools/qringbuffer/tst_qringbuffer.cpp b/tests/auto/corelib/tools/qringbuffer/tst_qringbuffer.cpp
index 4e14fd7a9b..145ba7ff72 100644
--- a/tests/auto/corelib/tools/qringbuffer/tst_qringbuffer.cpp
+++ b/tests/auto/corelib/tools/qringbuffer/tst_qringbuffer.cpp
@@ -45,6 +45,7 @@ private slots:
     void sizeWhenReserved();
     void free();
     void reserveAndRead();
+    void reserveAndReadInPacketMode();
     void reserveFrontAndRead();
     void chop();
     void ungetChar();
@@ -243,6 +244,25 @@ void tst_QRingBuffer::reserveAndRead()
     QCOMPARE(ringBuffer.size(), Q_INT64_C(0));
 }
 
+void tst_QRingBuffer::reserveAndReadInPacketMode()
+{
+    QRingBuffer ringBuffer(0);
+    // try to allocate 255 buffers
+    for (int i = 1; i < 256; ++i) {
+        char *ringPos = ringBuffer.reserve(i);
+        QVERIFY(ringPos);
+    }
+
+    // count and check the size of stored buffers
+    int buffersCount = 0;
+    while (!ringBuffer.isEmpty()) {
+        QByteArray ba = ringBuffer.read();
+        ++buffersCount;
+        QCOMPARE(ba.size(), buffersCount);
+    }
+    QCOMPARE(buffersCount, 255);
+}
+
 void tst_QRingBuffer::reserveFrontAndRead()
 {
     QRingBuffer ringBuffer;