QNetworkAccessManager: HTTP download performance improvements

Better usage of move semantics with implicit sharing to avoid
detaching (=malloc/memcpy). Also some other improvements.
Download performance improvement is around 20% according
to the httpDownloadPerformance autotest.

Reviewed-by: Thiago Macieira

1 files changed, 25 insertions, 15 deletions

diff --git a/src/network/access/qnetworkreplyimpl.cpp b/src/network/access/qnetworkreplyimpl.cpp
index 55b8b7f..44ae328 100644
--- a/src/network/access/qnetworkreplyimpl.cpp
+++ b/src/network/access/qnetworkreplyimpl.cpp
@@ -103,16 +103,17 @@ void QNetworkReplyImplPrivate::_q_copyReadyRead()
             break;
 
         bytesToRead = qBound<qint64>(1, bytesToRead, copyDevice->bytesAvailable());
-        char *ptr = readBuffer.reserve(bytesToRead);
-        qint64 bytesActuallyRead = copyDevice->read(ptr, bytesToRead);
+        QByteArray byteData;
+        byteData.resize(bytesToRead);
+        qint64 bytesActuallyRead = copyDevice->read(byteData.data(), byteData.size());
         if (bytesActuallyRead == -1) {
-            readBuffer.chop(bytesToRead);
+            byteData.clear();
             backendNotify(NotifyCopyFinished);
             break;
         }
 
-        if (bytesActuallyRead != bytesToRead)
-            readBuffer.chop(bytesToRead - bytesActuallyRead);
+        byteData.resize(bytesActuallyRead);
+        readBuffer.append(byteData);
 
         if (!copyDevice->isSequential() && copyDevice->atEnd()) {
             backendNotify(NotifyCopyFinished);
@@ -384,19 +385,17 @@ qint64 QNetworkReplyImplPrivate::nextDownstreamBlockSize() const
     if (readBufferMaxSize == 0)
         return DesiredBufferSize;
 
-    return qMax<qint64>(0, readBufferMaxSize - readBuffer.size());
+    return qMax<qint64>(0, readBufferMaxSize - readBuffer.byteAmount());
 }
 
 // we received downstream data and send this to the cache
 // and to our readBuffer (which in turn gets read by the user of QNetworkReply)
-void QNetworkReplyImplPrivate::appendDownstreamData(const QByteArray &data)
+void QNetworkReplyImplPrivate::appendDownstreamData(QByteDataBuffer &data)
 {
     Q_Q(QNetworkReplyImpl);
     if (!q->isOpen())
         return;
 
-    readBuffer.append(data);
-
     if (cacheEnabled && !cacheSaveDevice) {
         // save the meta data
         QNetworkCacheMetaData metaData;
@@ -415,10 +414,19 @@ void QNetworkReplyImplPrivate::appendDownstreamData(const QByteArray &data)
         }
     }
 
-    if (cacheSaveDevice)
-        cacheSaveDevice->write(data);
+    qint64 bytesWritten = 0;
+    for (int i = 0; i < data.bufferCount(); i++) {
+        QByteArray item = data[i];
+
+        if (cacheSaveDevice)
+            cacheSaveDevice->write(item.constData(), item.size());
+        readBuffer.append(item);
+
+        bytesWritten += item.size();
+    }
+    data.clear();
 
-    bytesDownloaded += data.size();
+    bytesDownloaded += bytesWritten;
     lastBytesDownloaded = bytesDownloaded;
 
     QPointer<QNetworkReplyImpl> qq = q;
@@ -427,6 +435,8 @@ void QNetworkReplyImplPrivate::appendDownstreamData(const QByteArray &data)
     pauseNotificationHandling();
     emit q->downloadProgress(bytesDownloaded,
                              totalSize.isNull() ? Q_INT64_C(-1) : totalSize.toLongLong());
+    // important: At the point of this readyRead(), the data parameter list must be empty,
+    // else implicit sharing will trigger memcpy when the user is reading data!
     emit q->readyRead();
 
     // hopefully we haven't been deleted here
@@ -602,14 +612,14 @@ void QNetworkReplyImpl::close()
 */
 qint64 QNetworkReplyImpl::bytesAvailable() const
 {
-    return QNetworkReply::bytesAvailable() + d_func()->readBuffer.size();
+    return QNetworkReply::bytesAvailable() + d_func()->readBuffer.byteAmount();
 }
 
 void QNetworkReplyImpl::setReadBufferSize(qint64 size)
 {
     Q_D(QNetworkReplyImpl);
     if (size > d->readBufferMaxSize &&
-        size == d->readBuffer.size())
+        size > d->readBuffer.byteAmount())
         d->backendNotify(QNetworkReplyImplPrivate::NotifyDownstreamReadyWrite);
 
     QNetworkReply::setReadBufferSize(size);
@@ -657,7 +667,7 @@ qint64 QNetworkReplyImpl::readData(char *data, qint64 maxlen)
         return 1;
     }
 
-    maxlen = qMin<qint64>(maxlen, d->readBuffer.size());
+    maxlen = qMin<qint64>(maxlen, d->readBuffer.byteAmount());
     return d->readBuffer.read(data, maxlen);
 }