org.apache.beam.sdk.transforms

Annotation Type DoFn.Teardown

@Documented
 @Retention(value=RUNTIME)
 @Target(value=METHOD)
public static @interface DoFn.Teardown

Annotation for the method to use to clean up this instance before it is discarded. No other method will be called after a call to the annotated method is made.

A runner will do its best to call this method on any given instance to prevent leaks of transient resources, however, there may be situations where this is impossible (e.g. process crash, hardware failure, etc.) or unnecessary (e.g. the pipeline is shutting down and the process is about to be killed anyway, so all transient resources will be released automatically by the OS). In these cases, the call may not happen. It will also not be retried, because in such situations the DoFn instance no longer exists, so there's no instance to retry it on. In portable execution(with --experiments=beam_fn_api), the exception thrown calling DoFn.Teardown will not fail the bundle execution. Instead, an error message will be shown on sdk harness log.

Thus, all work that depends on input elements, and all externally important side effects, must be performed in the DoFn.ProcessElement or DoFn.FinishBundle methods.

Example things that are a good idea to do in this method:

• Close a network connection that was opened in DoFn.Setup
• Shut down a helper process that was started in DoFn.Setup

Example things that MUST NOT be done in this method:

• Flushing a batch of buffered records to a database: this must be done in DoFn.FinishBundle.
• Deleting temporary files on a distributed filesystem: this must be done using the pipeline structure, e.g. using the Wait transform.

The method annotated with this must satisfy the following constraint:

• It must have zero arguments.