The shutdown method for ToplogyVersionObserver must interrupt the _workerOpCtx to ensure that the observer thread always returns (see here). However, the observer thread may create a new opCtx after checking if a shutdown is in progress (see here), violating this contract and introducing hangs. A simple fix to address this issue is to check the shutdown flag when holding the mutex and before setting _workerOpCtx.

{
    // Set the _workerOpCtx to our newly formed opCtxHandle before we unlock.
    stdx::lock_guard lk(_mutex);
    if (_shouldShutdown.load()) break;
    _workerOpCtx = opCtxHandle.get();
}