Fix QUdpSocket's emission of readyRead()

The documentation says that QUdpSocket emits readyRead() only for one
datagram and that if you don't read it, the class will not emit again.
That should be implemented by disabling of the socket notifier once we
have the datagram already read, but was broken.

In turn, that breakage caused a live-lock of the event loop: since we
didn't disable the notifier nor read the pending datagram, the event
loop would fire every time for the same datagram.

The re-enabling of the notifier was already working.

Task-number: QTBUG-43857
Change-Id: Ic5d393bfd36e48a193fcffff13bb32ad390b5fe8
Reviewed-by: Peter Hartmann <phartmann@blackberry.com>
Reviewed-by: Richard J. Moore <rich@kde.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/src/network/socket/qabstractsocket.cpp b/src/network/socket/qabstractsocket.cpp
index 604214ce8e..5a1ad40b90 100644
--- a/src/network/socket/qabstractsocket.cpp
+++ b/src/network/socket/qabstractsocket.cpp
@@ -740,8 +740,15 @@ bool QAbstractSocketPrivate::canReadNotification()
         return true;
     }
 
-    if ((isBuffered || socketType != QAbstractSocket::TcpSocket) && socketEngine)
-        socketEngine->setReadNotificationEnabled(readBufferMaxSize == 0 || readBufferMaxSize > q->bytesAvailable());
+    if (socketEngine) {
+        // turn the socket engine off if we've either:
+        // - got pending datagrams
+        // - reached the buffer size limit
+        if (isBuffered)
+            socketEngine->setReadNotificationEnabled(readBufferMaxSize == 0 || readBufferMaxSize > q->bytesAvailable());
+        else if (socketType != QAbstractSocket::TcpSocket)
+            socketEngine->setReadNotificationEnabled(!socketEngine->hasPendingDatagrams());
+    }
 
     // reset the read socket notifier state if we reentered inside the
     // readyRead() connected slot.