If two threads call executeFront() at the same time, it's possible that none of them executes any task, although there are permits available, and one of the threads just added a task in the queue. This scenario causes random initial state transfer timeouts in the testsuite:

    T1: continueTaskInBackground(): queue = empty, permits = 0
    T1: backgroundTaskFinished()
    T1: = semaphore.release(): queue = empty, permits = 1
    T1: = executeFront()
    T1: == semaphore.acquire() -> true: queue = empty, permits = 0
    T2: == queue.poll() -> null
    T2: submit(task)
    T2: = executeFront()
    T2: == semaphore.acquire() -> false
    T2: return without executing any task
    T1: return without executing any task