[FLINK-6684] Remove AsyncCheckpointRunnable from StreamTask

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Invalid
• Component/s: Runtime / State Backends
• Assignee: Bowen Li
• Reporter: Stefan Richter
• Created: 23/May/17 13:29
• Updated: 15/Oct/17 11:10
• Resolved: 15/Oct/17 11:10

Description

Right now, StreamTask executes AsyncCheckpointRunnable to run the async part of a snapshot. However, it seems that currently the main reason for executing this code in a separate tread is to avoid its execution under the checkpoint lock, so that processing can proceed.

Actually, the checkpoint is already triggered asynchronously, in Task::triggerCheckpointBarrier. We could also execute the checkpointing without executing AsyncCheckpointRunnable, by just running the code inside the thread that is spawned in Task::triggerCheckpointBarrier. We could simply

1) Run the synchronous part of the checkpoint under the checkpointing lock.
2) Run the asynchronous part of the checkpoint without holding the checkpointing lock.
3) Returning a Future from StatefulTask::triggerCheckpoint when called from Task::triggerCheckpointBarrier.

This would simplify the code and make the usage of the SafetyNetCloseableRegistry possible as intended.