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, 5 insertions, 5 deletions

diff --git a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
index 98bedea48a..524af5a2a7 100644
--- a/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
+++ b/src/plugins/platforms/xcb/qxcbnativeinterface.cpp
@@ -437,20 +437,20 @@ void QXcbNativeInterface::setAppUserTime(QScreen* screen, xcb_timestamp_t time)
 qint32 QXcbNativeInterface::generatePeekerId()
 {
     QXcbIntegration *integration = QXcbIntegration::instance();
-    return integration->defaultConnection()->generatePeekerId();
+    return integration->defaultConnection()->eventQueue()->generatePeekerId();
 }
 
 bool QXcbNativeInterface::removePeekerId(qint32 peekerId)
 {
     QXcbIntegration *integration = QXcbIntegration::instance();
-    return integration->defaultConnection()->removePeekerId(peekerId);
+    return integration->defaultConnection()->eventQueue()->removePeekerId(peekerId);
 }
 
-bool QXcbNativeInterface::peekEventQueue(QXcbConnection::PeekerCallback peeker, void *peekerData,
-                                         QXcbConnection::PeekOptions option, qint32 peekerId)
+bool QXcbNativeInterface::peekEventQueue(QXcbEventQueue::PeekerCallback peeker, void *peekerData,
+                                         QXcbEventQueue::PeekOptions option, qint32 peekerId)
 {
     QXcbIntegration *integration = QXcbIntegration::instance();
-    return integration->defaultConnection()->peekEventQueue(peeker, peekerData, option, peekerId);
+    return integration->defaultConnection()->eventQueue()->peekEventQueue(peeker, peekerData, option, peekerId);
 }
 
 void QXcbNativeInterface::setStartupId(const char *data)