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.

(cherry-picked from b32740001f735be9f0938f85d325dc2cf3dbe598)
Change-Id: I64bfb871d17c179f474d6672546e532566913a7f
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>

1 files changed, 9 insertions, 8 deletions

diff --git a/src/serialport/qserialport_win.cpp b/src/serialport/qserialport_win.cpp
index 73fedc03..5379b13a 100644
--- a/src/serialport/qserialport_win.cpp
+++ b/src/serialport/qserialport_win.cpp
@@ -508,20 +508,21 @@ bool QSerialPortPrivate::_q_completeAsyncRead()
         readStarted = false;
         return false;
     }
-    if (bytesTransferred > 0) {
+    if (bytesTransferred > 0)
         readBuffer.append(readChunkBuffer.left(bytesTransferred));
-        if (!emulateErrorPolicy())
-            emitReadyRead();
-    }
 
     readStarted = false;
 
+    bool result = true;
     if ((bytesTransferred == ReadChunkSize) && (policy == QSerialPort::IgnorePolicy))
-        return startAsyncRead();
+        result = startAsyncRead();
     else if (readBufferMaxSize == 0 || readBufferMaxSize > readBuffer.size())
-        return startAsyncCommunication();
-    else
-        return true;
+        result = startAsyncCommunication();
+
+    if ((bytesTransferred > 0) && !emulateErrorPolicy())
+        emitReadyRead();
+
+    return result;
 }
 
 bool QSerialPortPrivate::_q_completeAsyncWrite()