class TaskExecutor {
	final Object lockObject = new Object();
	final Set taskSet = Collections.synchronizedSet(new HashSet<Key>());
	
	void startTask(Key key) {
		synchronized(taskSet) {
			if (!taskSet.contains(key)) {
				executorService.submit(new Task(key));
	
				taskSet.add(key);
				activeTaskCountSemaphore.acquire();
	
			} else {
				throw new TaskException("Задача с данным ключем уже активна");
			}
		}
	}
	
	void onTaskComplete(Key key) {
		synchronized(taskSet) {
			taskSet.remove(key);
			activeTaskCountSemaphore.release();
		}
	}
}

	public int getActiveTaskCount() {
		return taskSet.size();
	}