Merge "transactions: fix mutex deadlock on layer death" into qt-dev

    while (mKeepRunning) {

        mConditionVariable.wait(mMutex);

        std::vector<ListenerStats> completedListenerStats;

        // For each listener

        auto completedTransactionsItr = mCompletedTransactions.begin();

            } else {

                completedTransactionsItr++;

            }

            completedListenerStats.push_back(std::move(listenerStats));

        }

        if (mPresentFence) {

            mPresentFence.clear();

        }

        // If everyone else has dropped their reference to a layer and its listener is dead,

        // we are about to cause the layer to be deleted. If this happens at the wrong time and

        // we are holding mMutex, we will cause a deadlock.

        //

        // The deadlock happens because this thread is holding on to mMutex and when we delete

        // the layer, it grabs SF's mStateLock. A different SF binder thread grabs mStateLock,

        // then call's TransactionCompletedThread::run() which tries to grab mMutex.

        //

        // To avoid this deadlock, we need to unlock mMutex when dropping our last reference to

        // to the layer.

        mMutex.unlock();

        completedListenerStats.clear();

        mMutex.lock();

    }

}