StreamTask with Mailbox.pdf

Our motivation behind this proposal is to simplify the threading model of stream tasks with a mailbox-based approach (similar to execution model commonly found in the actor-model). With the current threading model in Flink’s stream tasks, there are multiple threads that potentially want to access object states concurrently, for example event-processing and checkpoint triggering. Threads are shielded from each other through mutually exclusive access with a single “global” lock - the infamous checkpointing lock.