lukecwik commented on a change in pull request #12016:
URL: https://github.com/apache/beam/pull/12016#discussion_r448088312
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File path: sdks/java/core/src/main/java/org/apache/beam/sdk/transforms/DoFn.java
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@@ -1053,6 +1056,51 @@ public Duration getAllowedTimestampSkew() {
@Experimental(Kind.SPLITTABLE_DO_FN)
public @interface SplitRestriction {}
+ /**
+ * Annotation for the method that truncates the restriction of a <a
+ * href="https://s.apache.org/splittable-do-fn";>splittable</a> {@link DoFn}
into a bounded one to
+ * be processed when pipeline starts to drain.
+ *
+ * <p>This method is used to perform truncation of the restriction while it
is not actively being
+ * processed.
+ *
+ * <p>Signature: {@code void truncateRestriction(<arguments>);}
+ *
+ * <p>This method must satisfy the following constraints:
+ *
+ * <ul>
+ * <li>If one of the arguments is of type {@link OutputReceiver}, then it
will be passed an
+ * output receiver for outputting the truncated restrictions. All
truncated restrictions
+ * must be output through this parameter.
+ * <li>If one of its arguments is tagged with the {@link Element}
annotation, then it will be
+ * passed the current element being processed; the argument must be of
type {@code InputT}.
+ * Note that automatic conversion of {@link Row}s and {@link
FieldAccess} parameters are
+ * currently unsupported.
+ * <li>If one of its arguments is tagged with the {@link Restriction}
annotation, then it will
+ * be passed the current restriction being processed; the argument
must be of type {@code
+ * RestrictionT}.
+ * <li>If one of its arguments is tagged with the {@link Timestamp}
annotation, then it will be
+ * passed the timestamp of the current element being processed; the
argument must be of type
+ * {@link Instant}.
+ * <li>If one of its arguments is a {@link RestrictionTracker}, then it
will be passed a tracker
+ * that is initialized for the current {@link Restriction}. The
argument must be of the
+ * exact type {@code RestrictionTracker<RestrictionT, PositionT>}.
+ * <li>If one of its arguments is a subtype of {@link BoundedWindow}, then
it will be passed the
+ * window of the current element. When applied by {@link ParDo} the
subtype of {@link
+ * BoundedWindow} must match the type of windows on the input {@link
PCollection}. If the
+ * window is not accessed a runner may perform additional
optimizations.
+ * <li>If one of its arguments is of type {@link PaneInfo}, then it will
be passed information
+ * about the current triggering pane.
+ * <li>If one of the parameters is of type {@link PipelineOptions}, then
it will be passed the
+ * options for the current pipeline.
+ * </ul>
Review comment:
```suggestion
* </ul>
*
* <p>The default behavior when a pipeline is being drained is that {@link
IS_BOUNDED} restrictions process entirely while {@link IS_UNBOUNDED}
restrictions process till a checkpoint is possible. Splittable {@link DoFn}s
should only provide this method if they want to change this default behavior.
```
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