* @param completion - The completion of the asynchronous work
     * @throws IllegalStateException when new work is submitted for an operation while another thread is waiting in {@link #waitForCompletion(BuildOperationRef, ProjectLockRetention)} for the same operation.
     */
    void registerWork(BuildOperationRef operation, AsyncWorkCompletion completion);

    /**

        given:
        setupQueue(threads)
        def success = Mock(TestBuildOperation)

        when:
        runs.times { operationQueue.add(success) }

        and:
        operationQueue.waitForCompletion()

        then:
        runs * success.run(_)

        where:
        runs | threads
        0    | 1
        0    | 4
        0    | 10
        1    | 1
        1    | 4

            queue.cancel();
        }

        try {
            queue.waitForCompletion();
        } catch (MultipleBuildOperationFailures e) {
            failures.add(e);
        }

        if (failures.size() == 1) {
            throw failures.get(0);

        def operationFailures = [new Exception("failed operation 1"), new Exception("failed operation 2")]
        def buildQueue = Mock(BuildOperationQueue) {
            waitForCompletion() >> { throw new MultipleBuildOperationFailures(operationFailures, null) }
        }
        def buildOperationQueueFactory = Mock(BuildOperationQueueFactory) {
            create(_, _, _) >> { buildQueue }
        }

            handlers.add(handler);
            last = handler.getWaitPrecondition();
            return handler;
        } finally {
            lock.unlock();
        }
    }

    public void waitForCompletion() {
        cancelBlockedRequests();
        waitForRequestsToFinish();

        lock.lock();
        try {
            List<Throwable> failures = new ArrayList<Throwable>();

    }

    public void start() {
        server.start();
        running = true;
    }

    public void stop() {
        handler.waitForCompletion();
        running = false;
        // Stop is very slow, clean it up later
        EXECUTOR_SERVICE.execute(new Runnable() {
            @Override
            public void run() {

                // when performed from a worker thread (see DefaultBuildOperationQueue.waitForCompletion() which intentionally does not release the project locks while waiting)
                // TODO - add validation to fail eagerly when a worker attempts to lock a project
                //