Status

Current state: Under Discussion

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here [Change the link from KAFKA-1 to your own ticket]

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

When a Kafka Connect SourceTask is being stopped, the stop() method is called to signal that the task is to stop. However, this method is not necessarily the final method called and the stop() method can actually be called more than once in some situations for the same SourceTask. If the SourceTask has resources that it needs to clean up, there is no safe, easy-to-use way to achieve this. This KIP proposes the addition of a new stopped() method to the SourceTask interface which is guaranteed to be the final call in the SourceTask's lifecycle meaning that is can safely be used for cleaning up resources.

There is no need for an equivalent change on SinkTask because the shape of that interface makes it more clear when the task is safe to clean up its resources safely.

Public Interfaces

A new callback method is added to the SourceTask interface.

public abstract class SourceTask implements Task {

    /**

     * <p>

     * This task has stopped and can safely release resources.

     * </p>

     * <p>

     * SourceTasks are not required to implement this functionality. This hook is provided

     * for systems that have resources such as network connections that need to be

     * released safely once the SourceTask has indeed stopped.

     * </p>

     */

    public void stopped()

    {

        // This space intentionally left blank.

    }

}

Proposed Changes

Add the new stopped() callback to the SourceTask interface. In the Kafka Connect runtime, call this method as the final call to the SourceTask interface once it is known that all activity on the task has indeed stopped.

Compatibility, Deprecation, and Migration Plan

• This is a new optional callback that connectors do not have to implement. No migration concerns.

Rejected Alternatives

• Modify the Kafka Connect runtime so that stop() is called just once.