Fix events handling in waitForBytesWritten() method on Windows

In case of communication event is triggered in the
waitForBytesWritten() method then necessary to process it with
the _q_completeAsyncCommunication() method, but not with the
_q_completeAsyncRead() method.

Otherwise it leads to false filling of the readBuffer with the
data that were read earlier (or with garbage) which remained in
readChunkBuffer.

The synchronous loopback autotest reproduces a bug without of
this patch.

Tested on Windows 7/8 with the on-board and USB serial ports,
using Qt5.

Task-number: QTBUG-40344
Change-Id: I679109b60f4058c4c6f7e5f02c1f70ba6039d8d8
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>

2 files changed, 52 insertions, 5 deletions

diff --git a/src/serialport/qserialport_win.cpp b/src/serialport/qserialport_win.cpp
index 3432fc9..a6e1df7 100644
--- a/src/serialport/qserialport_win.cpp
+++ b/src/serialport/qserialport_win.cpp
@@ -449,8 +449,10 @@ bool QSerialPortPrivate::waitForBytesWritten(int msecs)
             return false;
         }
 
-        if (triggeredEvent == communicationOverlapped.hEvent
-                || triggeredEvent == readCompletionOverlapped.hEvent) {
+        if (triggeredEvent == communicationOverlapped.hEvent) {
+            if (!_q_completeAsyncCommunication())
+                return false;
+        } else if (triggeredEvent == readCompletionOverlapped.hEvent) {
             if (!_q_completeAsyncRead())
                 return false;
         } else if (triggeredEvent == writeCompletionOverlapped.hEvent) {
diff --git a/tests/auto/qserialport/tst_qserialport.cpp b/tests/auto/qserialport/tst_qserialport.cpp
index 192541c..4709d13 100644
--- a/tests/auto/qserialport/tst_qserialport.cpp
+++ b/tests/auto/qserialport/tst_qserialport.cpp
@@ -104,13 +104,15 @@ private slots:
     void waitForReadyReadWithOneByte();
     void waitForReadyReadWithAlphabet();
 
+    void twoStageSynchronousLoopback();
+
 protected slots:
     void handleBytesWrittenAndExitLoopSlot(qint64 bytesWritten);
     void handleBytesWrittenAndExitLoopSlot2(qint64 bytesWritten);
 
 private:
 #ifdef Q_OS_WIN
-    void clearReceiver();
+    void clearReceiver(const QString &customReceiverName = QString());
 #endif
 
     QString m_senderPortName;
@@ -142,9 +144,10 @@ tst_QSerialPort::tst_QSerialPort()
 // not expected). It is recommended to use this method for cleaning of
 // read FIFO of receiver for those tests in which reception of data is
 // required.
-void tst_QSerialPort::clearReceiver()
+void tst_QSerialPort::clearReceiver(const QString &customReceiverName)
 {
-    QSerialPort receiver(m_receiverPortName);
+    QSerialPort receiver(customReceiverName.isEmpty()
+                         ? m_receiverPortName : customReceiverName);
     if (receiver.open(QIODevice::ReadOnly))
         enterLoopMsecs(100);
 }
@@ -438,5 +441,47 @@ void tst_QSerialPort::waitForReadyReadWithAlphabet()
     QVERIFY(readyReadSpy.count() > 0);
 }
 
+void tst_QSerialPort::twoStageSynchronousLoopback()
+{
+#ifdef Q_OS_WIN
+    clearReceiver();
+    clearReceiver(m_senderPortName);
+#endif
+
+    QSerialPort senderPort(m_senderPortName);
+    QVERIFY(senderPort.open(QSerialPort::ReadWrite));
+
+    QSerialPort receiverPort(m_receiverPortName);
+    QVERIFY(receiverPort.open(QSerialPort::ReadWrite));
+
+    const int waitMsecs = 50;
+
+    // first stage
+    senderPort.write(newlineArray);
+    senderPort.waitForBytesWritten(waitMsecs);
+    QTest::qSleep(waitMsecs);
+    receiverPort.waitForReadyRead(waitMsecs);
+    QCOMPARE(newlineArray.size(), receiverPort.bytesAvailable());
+    receiverPort.write(receiverPort.readAll());
+    receiverPort.waitForBytesWritten(waitMsecs);
+    QTest::qSleep(waitMsecs);
+    senderPort.waitForReadyRead(waitMsecs);
+    QCOMPARE(newlineArray.size(), senderPort.bytesAvailable());
+    QCOMPARE(newlineArray, senderPort.readAll());
+
+    // second stage
+    senderPort.write(newlineArray);
+    senderPort.waitForBytesWritten(waitMsecs);
+    QTest::qSleep(waitMsecs);
+    receiverPort.waitForReadyRead(waitMsecs);
+    QCOMPARE(newlineArray.size(), receiverPort.bytesAvailable());
+    receiverPort.write(receiverPort.readAll());
+    receiverPort.waitForBytesWritten(waitMsecs);
+    QTest::qSleep(waitMsecs);
+    senderPort.waitForReadyRead(waitMsecs);
+    QCOMPARE(newlineArray.size(), senderPort.bytesAvailable());
+    QCOMPARE(newlineArray, senderPort.readAll());
+}
+
 QTEST_MAIN(tst_QSerialPort)
 #include "tst_qserialport.moc"