Fix reading when switching from asynchronous to synchronous approach

If one wants to use the asynchronous approach (using the signals and
slots), and then - the synchronous (using the waitForXX functions) then
synchronous reading stalls because the waitForReadyRead() method
always returns the TimeoutError code.

The reason is that the signal readyRead() is emitted before the
startAsyncRead() (or the startAsyncCommunication()) called inside of
completeAsyncRead().

Need to emit the readyRead() only after the next asynchronous reading
(the startAsyncRead() or the startAsyncCommunication()) was cocked.

Now the behavior is similar to behavior of QWindowsPipeReader. Besides,
the auto-test which reveals this issue is added.

Tested with the virtual com0com serial ports, using the auto-tests and
set of the examples.

Change-Id: I64bfb871d17c179f474d6672546e532566913a7f
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>
Reviewed-by: Andrzej Ostruszka <andrzej.ostruszka@gmail.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/src/serialport/qserialport_win.cpp b/src/serialport/qserialport_win.cpp
index b01d2d0e..57b70966 100644
--- a/src/serialport/qserialport_win.cpp
+++ b/src/serialport/qserialport_win.cpp
@@ -426,18 +426,20 @@ bool QSerialPortPrivate::completeAsyncRead(qint64 bytesTransferred)
     if (bytesTransferred > 0) {
         char *ptr = buffer.reserve(bytesTransferred);
         ::memcpy(ptr, readChunkBuffer.constData(), bytesTransferred);
-        if (!emulateErrorPolicy())
-            emitReadyRead();
     }
 
     readStarted = false;
 
+    bool result = true;
     if ((bytesTransferred == ReadChunkSize) && (policy == QSerialPort::IgnorePolicy))
-        return startAsyncRead();
+        result = startAsyncRead();
     else if (readBufferMaxSize == 0 || readBufferMaxSize > buffer.size())
-        return startAsyncCommunication();
-    else
-        return true;
+        result = startAsyncCommunication();
+
+    if ((bytesTransferred > 0) && !emulateErrorPolicy())
+        emitReadyRead();
+
+    return result;
 }
 
 bool QSerialPortPrivate::completeAsyncWrite(qint64 bytesTransferred)