class DefaultResourceTracker implements ResourceTracker {

	@Override
	public Collection<ResourceRequirement> getAcquiredResources(JobID jobId) {
		Preconditions.checkNotNull(jobId);
		JobScopedResourceTracker tracker = trackers.get(jobId);
		return tracker == null
			? Collections.emptyList()
			: tracker.getAcquiredResources();
	}

}