Don't lock render thread when blocking swap is used

By default, Qt will use a non-blocking eglSwapBuffers() and
implement our own frame event mechanism with a time-out.

When the blocking version of eglSwapBuffers() is in use (either
because it's manually enabled or because the driver does not
support the alternative), it depends on the main thread to
poll events, as it will wait indefinitely for a frame callback.

This is incompatible with our locking of the surface for the
duration of the frame, since we may end up locking the main
thread in QWaylandWindow::reset() during shutdown while the
render thread is simultaneously locked in eglSwapBuffers().

The lock was implemented to work around a bug in one family of
graphics drivers, so we simply disable it when blocking
eglSwapBuffers() is used. If we need to put this back, we would
need a more advanced approach and make sure we continue to poll
events even while we're waiting for access to the surface.

Pick-to: 6.5
Fixes: QTBUG-118890
Change-Id: I04f7d2b168726d82c38fe3fafd350dcab928b956
Reviewed-by: David Edmundson <davidedmundson@kde.org>
(cherry picked from commit 02263f21f5cdd61d71e5e8e08b2e73c05c6c1e76)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit b0f96ca63ee89f06254d65a8aca780c0d61933b4)

1 files changed, 4 insertions, 2 deletions

diff --git a/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp b/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp
index e10b89813..039ec1a6a 100644
--- a/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp
+++ b/src/hardwareintegration/client/wayland-egl/qwaylandglcontext.cpp
@@ -274,13 +274,15 @@ QWaylandGLContext::~QWaylandGLContext()
 void QWaylandGLContext::beginFrame()
 {
     Q_ASSERT(m_currentWindow != nullptr);
-    m_currentWindow->beginFrame();
+    if (m_supportNonBlockingSwap)
+        m_currentWindow->beginFrame();
 }
 
 void QWaylandGLContext::endFrame()
 {
     Q_ASSERT(m_currentWindow != nullptr);
-    m_currentWindow->endFrame();
+    if (m_supportNonBlockingSwap)
+        m_currentWindow->endFrame();
 }
 
 bool QWaylandGLContext::makeCurrent(QPlatformSurface *surface)