From 5b78d7fdcf9b758f117eaa65dc5eeddd0d4557e0 Mon Sep 17 00:00:00 2001
From: Alex Trotsenko <alex1973tr@gmail.com>
Date: Fri, 7 May 2021 18:16:17 +0300
Subject: QLocalSocket/Win: avoid double buffering on write

As QWindowsPipeWriter now maintains a chunk queue, there is no need to
use the internal QIODevice buffer and wait for the previous operation
to complete.

Change-Id: Id4d54edfe920aeb4a534980cb0cc85a56c067a70
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
---
 src/corelib/io/qiodevice.cpp          |  4 +---
 src/corelib/io/qiodevice_p.h          |  7 +++++++
 src/corelib/io/qwindowspipewriter.cpp | 29 +++++++++++++++++++++++------
 src/corelib/io/qwindowspipewriter_p.h |  5 +++++
 4 files changed, 36 insertions(+), 9 deletions(-)

(limited to 'src/corelib')

diff --git a/src/corelib/io/qiodevice.cpp b/src/corelib/io/qiodevice.cpp
index f3354cad65..3e3ee6e406 100644
--- a/src/corelib/io/qiodevice.cpp
+++ b/src/corelib/io/qiodevice.cpp
@@ -1763,9 +1763,7 @@ qint64 QIODevice::write(const QByteArray &data)
 */
 void QIODevicePrivate::write(const char *data, qint64 size)
 {
-    if (currentWriteChunk != nullptr
-        && currentWriteChunk->constData() == data
-        && currentWriteChunk->size() == size) {
+    if (isWriteChunkCached(data, size)) {
         // We are called from write(const QByteArray &) overload.
         // So, we can make a shallow copy of chunk.
         writeBuffer.append(*currentWriteChunk);
diff --git a/src/corelib/io/qiodevice_p.h b/src/corelib/io/qiodevice_p.h
index 3f8e459d88..3639418bbc 100644
--- a/src/corelib/io/qiodevice_p.h
+++ b/src/corelib/io/qiodevice_p.h
@@ -185,6 +185,13 @@ public:
     qint64 skipByReading(qint64 maxSize);
     void write(const char *data, qint64 size);
 
+    inline bool isWriteChunkCached(const char *data, qint64 size) const
+    {
+        return currentWriteChunk != nullptr
+               && currentWriteChunk->constData() == data
+               && currentWriteChunk->size() == size;
+    }
+
 #ifdef QT_NO_QOBJECT
     QIODevice *q_ptr = nullptr;
 #endif
diff --git a/src/corelib/io/qwindowspipewriter.cpp b/src/corelib/io/qwindowspipewriter.cpp
index f2f4dce056..cfa486451c 100644
--- a/src/corelib/io/qwindowspipewriter.cpp
+++ b/src/corelib/io/qwindowspipewriter.cpp
@@ -121,16 +121,35 @@ qint64 QWindowsPipeWriter::bytesToWrite() const
 }
 
 /*!
-    Writes data to the pipe.
+    Writes a shallow copy of \a ba to the internal buffer.
  */
 bool QWindowsPipeWriter::write(const QByteArray &ba)
+{
+    return writeImpl(ba);
+}
+
+/*!
+    Writes data to the internal buffer.
+ */
+bool QWindowsPipeWriter::write(const char *data, qint64 size)
+{
+    return writeImpl(data, size);
+}
+
+template <typename... Args>
+inline bool QWindowsPipeWriter::writeImpl(Args... args)
 {
     QMutexLocker locker(&mutex);
 
     if (lastError != ERROR_SUCCESS)
         return false;
 
-    writeBuffer.append(ba);
+    writeBuffer.append(args...);
+    return writeImplTail(&locker);
+}
+
+bool QWindowsPipeWriter::writeImplTail(QMutexLocker<QMutex> *locker)
+{
     if (writeSequenceStarted)
         return true;
 
@@ -143,10 +162,10 @@ bool QWindowsPipeWriter::write(const QByteArray &ba)
 
     if (!winEventActPosted) {
         winEventActPosted = true;
-        locker.unlock();
+        locker->unlock();
         QCoreApplication::postEvent(this, new QEvent(QEvent::WinEventAct));
     } else {
-        locker.unlock();
+        locker->unlock();
     }
 
     SetEvent(syncHandle);
@@ -232,8 +251,6 @@ void QWindowsPipeWriter::waitCallback(PTP_CALLBACK_INSTANCE instance, PVOID cont
 bool QWindowsPipeWriter::writeCompleted(DWORD errorCode, DWORD numberOfBytesWritten)
 {
     if (errorCode == ERROR_SUCCESS) {
-        Q_ASSERT(numberOfBytesWritten == DWORD(writeBuffer.nextDataBlockSize()));
-
         bytesWrittenPending = true;
         pendingBytesWrittenValue += numberOfBytesWritten;
         writeBuffer.free(numberOfBytesWritten);
diff --git a/src/corelib/io/qwindowspipewriter_p.h b/src/corelib/io/qwindowspipewriter_p.h
index cb78195a85..f8cabb225d 100644
--- a/src/corelib/io/qwindowspipewriter_p.h
+++ b/src/corelib/io/qwindowspipewriter_p.h
@@ -69,6 +69,7 @@ public:
     ~QWindowsPipeWriter();
 
     bool write(const QByteArray &ba);
+    bool write(const char *data, qint64 size);
     void stop();
     bool waitForWrite(int msecs);
     bool checkForWrite() { return consumePendingAndEmit(false); }
@@ -83,6 +84,10 @@ protected:
     bool event(QEvent *e) override;
 
 private:
+    template <typename... Args>
+    inline bool writeImpl(Args... args);
+    bool writeImplTail(QMutexLocker<QMutex> *locker);
+
     void startAsyncWriteLocked();
     static void CALLBACK waitCallback(PTP_CALLBACK_INSTANCE instance, PVOID context,
                                       PTP_WAIT wait, TP_WAIT_RESULT waitResult);
-- 
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