Fix deadlocks on WebEngineContext destruction

This patch aims to handle 3 deadlocks on exit:

(1) Do not attempt to restart Viz thread on shutdown,
    this will make deadlock with no separate gpu thread,
    since force shut down of FrameSinkManager requires
    interaction with gpu process.

(2) QCoreApplication, QGuiApplication, QApplication
    behave differently when doing qt post routine,
    ~QGuiApplication calls the post routine handler after
    closing event dispatcher, which will on windows stop processing
    timer events, which we need to pump message loop when
    shuting down viz. Do not use QEventLoop and switch
    to active pulling. The proper solution is to fix QGuiApplication
    destructor to call post routine first, but this change  might
    have side effects on already existing user code.

(3) Since 7f1649b438329e we delete root frame sink asynchronously,
    which will in gpu thread running in separate thread create a deadlock.
    Viz requires gpu to destruct root frame sink, however if main process
    tries to close gpu process this will in turn try close viz, but viz calls
    back gpu now since the root frame sink is not destroyed.
    Use the same solution as in (1).

Change-Id: Ic6bc904bdac90ee01a5c5b9398a2e2746be3bbd8
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>

0 files changed, 0 insertions, 0 deletions