QCFSocketNotifier: fix registering a source in the run loop

Even if a callback type is not automatically re-enabled, callbacks are implicitly enabled when the source has been added to the run loop. In this case, calling CFSocketEnableCallBacks() could produce an extra notification if there is a pending event in the queue. The bug is quite unstable and completely depends on the internal OS delays. So, it can't be tested inside Qt. Task-number: QTBUG-59930 Change-Id: I751b8b8cf99cb86b80055f2214a42a638f01abe4 Reviewed-by: Timur Pocheptsov <[email protected]>
vellw · May 3, 2017 · 979c8b7 · 979c8b7
1 parent 0fefed9
commit 979c8b7
Showing 1 changed file with 11 additions and 2 deletions.
diff --git a/src/corelib/kernel/qcfsocketnotifier.cpp b/src/corelib/kernel/qcfsocketnotifier.cpp
@@ -292,10 +292,19 @@ void QCFSocketNotifier::enableSocketNotifiers(CFRunLoopObserverRef ref, CFRunLoo
                 continue;
             }
 
-            if (!socketInfo->readNotifier)
+            // Apple docs say: "If a callback is automatically re-enabled,
+            // it is called every time the condition becomes true ... If a
+            // callback is not automatically re-enabled, then it gets called
+            // exactly once, and is not called again until you manually
+            // re-enable that callback by calling CFSocketEnableCallBacks()".
+            // So, we don't need to enable callbacks on registering.
+            socketInfo->readEnabled = (socketInfo->readNotifier != nullptr);
+            if (!socketInfo->readEnabled)
                 CFSocketDisableCallBacks(socketInfo->socket, kCFSocketReadCallBack);
-            if (!socketInfo->writeNotifier)
+            socketInfo->writeEnabled = (socketInfo->writeNotifier != nullptr);
+            if (!socketInfo->writeEnabled)
                 CFSocketDisableCallBacks(socketInfo->socket, kCFSocketWriteCallBack);
+            continue;
         }
 
         if (socketInfo->readNotifier && !socketInfo->readEnabled) {