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Fix possible race condition leading to a dead lock

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It is a bit dangerous to call wl_display_dispatch() in the event thread,
since it may race with the dispatch called e.g. in QWaylandDisplay's
blockingReadEvents() and lead to a dead lock. Instead, use wl_display_prepare_read()
and wl_display_read_events() in the event thread, which doesn't block, and only
dispatch in QWaylandDisplay.
As a result we don't need the additional wayland queue anymore, so remove it.

Change-Id: I9fbbe5d2f38d06773beb7847df1a0212cca92c37
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>
This commit is contained in:
Giulio Camuffo 2015-06-17 14:48:44 +03:00
parent 837c740cd6
commit 0b71d61d37
4 changed files with 6 additions and 20 deletions
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14
src/plugins/platforms/wayland/qwaylanddisplay.cpp
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@ -147,12 +147,7 @@ QWaylandDisplay::QWaylandDisplay(QWaylandIntegration *waylandIntegration)
mEventThreadObject->displayConnect();
mDisplay = mEventThreadObject->display(); //blocks until display is available
//Create a new even queue for the QtGui thread
mEventQueue = wl_display_create_queue(mDisplay);
struct ::wl_registry *registry = wl_display_get_registry(mDisplay);
wl_proxy_set_queue((struct wl_proxy *)registry, mEventQueue);
init(registry);
connect(mEventThreadObject, SIGNAL(newEventsRead()), this, SLOT(flushRequests()));
@ -180,7 +175,7 @@ QWaylandDisplay::~QWaylandDisplay(void)
void QWaylandDisplay::flushRequests()
{
if (wl_display_dispatch_queue_pending(mDisplay, mEventQueue) < 0) {
if (wl_display_dispatch_pending(mDisplay) < 0) {
mEventThreadObject->checkError();
exitWithError();
}
@ -191,7 +186,7 @@ void QWaylandDisplay::flushRequests()
void QWaylandDisplay::blockingReadEvents()
{
if (wl_display_dispatch_queue(mDisplay, mEventQueue) < 0) {
if (wl_display_dispatch(mDisplay) < 0) {
mEventThreadObject->checkError();
exitWithError();
}
@ -345,17 +340,16 @@ void QWaylandDisplay::forceRoundTrip()
int ret = 0;
bool done = false;
wl_callback *callback = wl_display_sync(mDisplay);
wl_proxy_set_queue((struct wl_proxy *)callback, mEventQueue);
wl_callback_add_listener(callback, &sync_listener, &done);
flushRequests();
if (QThread::currentThread()->eventDispatcher()) {
while (!done && ret >= 0) {
QThread::currentThread()->eventDispatcher()->processEvents(QEventLoop::WaitForMoreEvents);
ret = wl_display_dispatch_queue_pending(mDisplay, mEventQueue);
ret = wl_display_dispatch_pending(mDisplay);
}
} else {
while (!done && ret >= 0)
ret = wl_display_dispatch_queue(mDisplay, mEventQueue);
ret = wl_display_dispatch(mDisplay);
}
if (ret == -1 && !done)

2
src/plugins/platforms/wayland/qwaylanddisplay_p.h
View File

@ -108,7 +108,6 @@ public:
void setCursor(struct wl_buffer *buffer, struct wl_cursor_image *image);
struct wl_display *wl_display() const { return mDisplay; }
struct wl_event_queue *wl_event_queue() const { return mEventQueue; }
struct ::wl_registry *wl_registry() { return object(); }
const struct wl_compositor *wl_compositor() const { return mCompositor.object(); }
@ -175,7 +174,6 @@ private:
};
struct wl_display *mDisplay;
struct wl_event_queue *mEventQueue;
QtWayland::wl_compositor mCompositor;
struct wl_shm *mShm;
QThread *mEventThread;

8
src/plugins/platforms/wayland/qwaylandeventthread.cpp
View File

@ -80,13 +80,9 @@ void QWaylandEventThread::checkError() const
void QWaylandEventThread::readWaylandEvents()
{
if (wl_display_dispatch(m_display) < 0) {
checkError();
m_readNotifier->setEnabled(false);
emit fatalError();
return;
if (wl_display_prepare_read(m_display) == 0) {
wl_display_read_events(m_display);
}
emit newEventsRead();
}

2
src/plugins/platforms/wayland/qwaylandnativeinterface.cpp
View File

@ -58,8 +58,6 @@ void *QWaylandNativeInterface::nativeResourceForIntegration(const QByteArray &re
if (lowerCaseResource == "display" || lowerCaseResource == "wl_display" || lowerCaseResource == "nativedisplay")
return m_integration->display()->wl_display();
if (lowerCaseResource == "wl_event_queue")
return m_integration->display()->wl_event_queue();
if (lowerCaseResource == "compositor")
return const_cast<wl_compositor *>(m_integration->display()->wl_compositor());
if (lowerCaseResource == "server_buffer_integration")