[REEF-1545] Refactor HandlerContainer to improve safety, readability, and performance

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.16
• Component/s: REEF-Common
• Labels: javadoc performance race-condition refactor
• Assignee: Sergiy Matusevych
• Reporter: Sergiy Matusevych
• Created: 24/Aug/16 22:57
• Updated: 12/Sep/16 19:56
• Resolved: 27/Aug/16 00:15

Description

Current implementation of HandlerContainer class has several issues:

• It uses the Subscription class in untyped fashion, ignoring its type parameter.
• .unsubscribe() method manually checks for all possible types of the subscription token, even though it is always known at the subscription time. This is error-prone and hard to read.
• When registering handlers, we use a sequence of two operations - Map.putIfAbsent() and .replace(), instead of just .put(). It also introduces a potential race condition, since the map is synchronized.