xcb: lock-free event processing

For details how this works refer to the documentation in the patch.

The follow-up patches will switch to calling processXcbEvents() on every
event loop iteration. With the existing code that would mean frequent
locking of shared data (event queue). Acquiring a lock is fast, but
lock contention isn't. To avoid potential problems, reimplement xcb event
processing to be lock-free. Besides theoretical performance benefits,
this definitally improves code readability in qxcbconnection.cpp. Thanks
to Mikhail Svetkin for questioning the design of the existing code.

Done-with: Mikhail Svetkin <mikhail.svetkin@qt.io>
Change-Id: I935f2b6ca802580f5c80205aef7b2f9afc172d26
Reviewed-by: Mikhail Svetkin <mikhail.svetkin@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/plugins/platforms/xcb/qxcbnativeinterface.h b/src/plugins/platforms/xcb/qxcbnativeinterface.h
index d1f2747bea..4656f46be5 100644
--- a/src/plugins/platforms/xcb/qxcbnativeinterface.h
+++ b/src/plugins/platforms/xcb/qxcbnativeinterface.h
@@ -118,8 +118,8 @@ public:
 
     static qint32 generatePeekerId();
     static bool removePeekerId(qint32 peekerId);
-    static bool peekEventQueue(QXcbConnection::PeekerCallback peeker, void *peekerData = nullptr,
-                               QXcbConnection::PeekOptions option = QXcbConnection::PeekDefault,
+    static bool peekEventQueue(QXcbEventQueue::PeekerCallback peeker, void *peekerData = nullptr,
+                               QXcbEventQueue::PeekOptions option = QXcbEventQueue::PeekDefault,
                                qint32 peekerId = -1);
 
     Q_INVOKABLE QString dumpConnectionNativeWindows(const QXcbConnection *connection, WId root) const;