ServiceManager.WritingThread throws ConcurrentModificationException occasionally

ServiceManager.WritingThread can throw ConcurrentModificationException, because its HashMap members are not thread-safe and are modified from both ServiceManager's thread and from WritingThread's thread.
For example ConcurrentModificationException occurs when WritingThread runs by HashMap keys in WritingThread.write() method and at the same time ServiceManager changes the same HashMap via public WritingThread.remove() method.