Optimize QThreadPrivate::addObjectWithPendingBindingStatusChange()

... and bindingStatus()

QBindingStatus* is the final state of the value chain in
m_statusOrPendingObjects, so we can use the Double-Checked Locking
Pattern to avoid locking the mutex when we already have a status - it
won't go away again, unlike the vector in the List state.

To enable the change, make the data member an atomic<>. All loads and
stores can continue to use memory_order::relaxed, except the loads of
a potential status, which have to acquire, and the store of the
status, which has to release. This creates the necessary
synchronizes-with relation. So even though we synchronize out of
middle of the mutex critical section in QThread::exec() this way,
there's no data race between QThread::exec() and a potential
bindingStatus() call.

Change-Id: I0e0b7bd305649fa5f56a0f8723fb75f2577b90dd
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

0 files changed, 0 insertions, 0 deletions