Merge remote-tracking branch 'origin/tqtc/lts-5.15.13' into tqtc/lts-5.15-opensourcev5.15.13-lts-lgpl

Change-Id: I7053ce5196cadf7069fb018d2f8415d3269a8c20

1 files changed, 10 insertions, 1 deletions

diff --git a/src/serialport/qwinoverlappedionotifier.cpp b/src/serialport/qwinoverlappedionotifier.cpp
index 2090004b..8ec5c1a8 100644
--- a/src/serialport/qwinoverlappedionotifier.cpp
+++ b/src/serialport/qwinoverlappedionotifier.cpp
@@ -396,8 +396,8 @@ void QWinOverlappedIoNotifierPrivate::notify(DWORD numberOfBytes, DWORD errorCod
     Q_Q(QWinOverlappedIoNotifier);
     WaitForSingleObject(hResultsMutex, INFINITE);
     results.enqueue(IOResult(numberOfBytes, errorCode, overlapped));
-    ReleaseMutex(hResultsMutex);
     ReleaseSemaphore(hSemaphore, 1, NULL);
+    ReleaseMutex(hResultsMutex);
     // Do not send a signal if we didn't process the previous one.
     // This is done to prevent soft memory leaks when working in a completely
     // synchronous way.
@@ -417,6 +417,15 @@ void QWinOverlappedIoNotifierPrivate::_q_notified()
         WaitForSingleObject(hResultsMutex, INFINITE);
         QQueue<IOResult> values;
         results.swap(values);
+        // Decreasing the semaphore count to keep it in sync with the number
+        // of messages in queue. As ReleaseSemaphore does not accept negative
+        // values, this is sort of a recommended way to go:
+        // https://learn.microsoft.com/en-us/windows/win32/api/synchapi/nf-synchapi-releasesemaphore#remarks
+        int numToDecrease = values.size() - 1;
+        while (numToDecrease > 0) {
+            WaitForSingleObject(hSemaphore, 0);
+            --numToDecrease;
+        }
         ReleaseMutex(hResultsMutex);
         // 'q' can go out of scope if the user decides to close the serial port
         // while processing some answer. So we need to guard against that.