Make the function pointer to xcb_poll_for_queued_event not a member

In the normal case, this change is a no-op. In case RTLD_DEFAULT isn't
defined, this makes the job of the optimizer easier to detect that the
static variable is never modified and that it can do a lot of dead code
elimination.

This also enables the optimization in the next commit.

Change-Id: Ib306f8f647014b399b87ffff13f12f40a359233b
Reviewed-by: Gatis Paeglis <gatis.paeglis@digia.com>

1 files changed, 20 insertions, 13 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index 29e1fd145d..2158300591 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -77,6 +77,21 @@
 #include <xcb/render.h>
 #endif
 
+typedef xcb_generic_event_t * (*XcbPollForQueuedEventFunctionPointer)(xcb_connection_t *c);
+static XcbPollForQueuedEventFunctionPointer local_xcb_poll_for_queued_event;
+
+static inline void checkXcbPollForQueuedEvent()
+{
+#ifdef RTLD_DEFAULT
+    local_xcb_poll_for_queued_event = (XcbPollForQueuedEventFunctionPointer)dlsym(RTLD_DEFAULT, "xcb_poll_for_queued_event");
+#endif
+
+#ifdef Q_XCB_DEBUG
+    if (local_xcb_poll_for_queued_event)
+        qDebug("Using threaded event reader with xcb_poll_for_queued_event");
+#endif
+}
+
 QT_BEGIN_NAMESPACE
 
 Q_LOGGING_CATEGORY(lcQpaXInput, "qt.qpa.input")
@@ -1169,21 +1184,13 @@ void QXcbConnection::addPeekFunc(PeekFunc f)
 
 QXcbEventReader::QXcbEventReader(QXcbConnection *connection)
     : m_connection(connection)
-    , m_xcb_poll_for_queued_event(0)
 {
-#ifdef RTLD_DEFAULT
-    m_xcb_poll_for_queued_event = (XcbPollForQueuedEventFunctionPointer)dlsym(RTLD_DEFAULT, "xcb_poll_for_queued_event");
-#endif
-
-#ifdef Q_XCB_DEBUG
-    if (m_xcb_poll_for_queued_event)
-        qDebug("Using threaded event reader with xcb_poll_for_queued_event");
-#endif
+    checkXcbPollForQueuedEvent();
 }
 
 void QXcbEventReader::start()
 {
-    if (m_xcb_poll_for_queued_event) {
+    if (local_xcb_poll_for_queued_event) {
         connect(this, SIGNAL(eventPending()), m_connection, SLOT(processXcbEvents()), Qt::QueuedConnection);
         connect(this, SIGNAL(finished()), m_connection, SLOT(processXcbEvents()));
         QThread::start();
@@ -1209,7 +1216,7 @@ void QXcbEventReader::registerEventDispatcher(QAbstractEventDispatcher *dispatch
     // flush the xcb connection before the EventDispatcher is going to block
     // In the non-threaded case processXcbEvents is called before going to block,
     // which flushes the connection.
-    if (m_xcb_poll_for_queued_event)
+    if (local_xcb_poll_for_queued_event)
         connect(dispatcher, SIGNAL(aboutToBlock()), m_connection, SLOT(flush()));
 }
 
@@ -1219,7 +1226,7 @@ void QXcbEventReader::run()
     while (m_connection && (event = xcb_wait_for_event(m_connection->xcb_connection()))) {
         m_mutex.lock();
         addEvent(event);
-        while (m_connection && (event = m_xcb_poll_for_queued_event(m_connection->xcb_connection())))
+        while (m_connection && (event = local_xcb_poll_for_queued_event(m_connection->xcb_connection())))
             addEvent(event);
         m_mutex.unlock();
         emit eventPending();
@@ -1243,7 +1250,7 @@ void QXcbEventReader::addEvent(xcb_generic_event_t *event)
 QXcbEventArray *QXcbEventReader::lock()
 {
     m_mutex.lock();
-    if (!m_xcb_poll_for_queued_event) {
+    if (!local_xcb_poll_for_queued_event) {
         while (xcb_generic_event_t *event = xcb_poll_for_event(m_connection->xcb_connection()))
             m_events << event;
     }