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• The close(timeout) should work when called from a user caller thread or the internal sender thread.
• In sender thread only close(-1, TimeUnit.MILLISECONDS) should be called because:
  
  • close() or close(0, TimeUnit.MILLISECONDS) should not be called because that will make producer block forever.
  • close(500, TimeUnit.MILLISECONDS) has the same effect as close(-1, TimeUnit.MILLISECONDS) only except it will block for 500 milliseconds.
• Because it is possible the close(timeout) is called for multiple times, it has to be idempotent.

Proposed Changes

To close a producer forcefully, the following changes are going to be made:

1.  Add a forceClose flag to sender.
2. When forceClose flag is set, sender will not send any more messages but fail all the messages in RecordAccumulator and wake up the threads waiting on a callback. These threads may be doing:
   
   1. synchronized send
   2. flush()
3. Cleanup metrics and release other resources.

When close(positive, TimeUnit.MILLISECONDS) is called, it will try to do a normal close first. If the normal close did not finish before timeout, it then close the producer forcefully.

Compatibility, Deprecation, and Migration Plan

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