AHeise commented on a change in pull request #10435: [FLINK-13955][runtime]
migrate ContinuousFileReaderOperator to the mailbox execution model
URL: https://github.com/apache/flink/pull/10435#discussion_r370051507
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File path:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/functions/source/ContinuousFileReaderOperator.java
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@@ -54,39 +62,157 @@
* {@link ContinuousFileMonitoringFunction}. Contrary to the {@link
ContinuousFileMonitoringFunction}
* which has a parallelism of 1, this operator can have DOP > 1.
*
- * <p>As soon as a split descriptor is received, it is put in a queue, and
have another
- * thread read the actual data of the split. This architecture allows the
separation of the
- * reading thread from the one emitting the checkpoint barriers, thus removing
any potential
- * back-pressure.
+ * <p>This implementation uses {@link MailboxExecutor} to execute each action
and states:<ol>
+ * <li>start in {@link ReaderState#IDLE IDLE}</li>
+ * <li>upon receiving a split add it to the queue, switch to {@link
ReaderState#OPENING OPENING} and enqueue a
+ * {@link org.apache.flink.streaming.runtime.tasks.mailbox.Mail mail} with
self as {@link Runnable}</li>
+ * <li>open file, switch to {@link ReaderState#READING READING}, read one
record, re-enqueue self</li>
+ * <li>if no more records or splits available, switch back to {@link
ReaderState#IDLE IDLE}</li>
+ * </ol>
+ * On close:
+ * <ol>
+ * <li>if {@link ReaderState#IDLE IDLE} then close immediately</li>
+ * <li>otherwise switch to {@link ReaderState#CLOSING CLOSING}, call
{@link MailboxExecutor#yield() yield} in a loop
+ * until state is {@link ReaderState#CLOSED CLOSED}</li>
+ * <li>{@link MailboxExecutor#yield() yield()} causes remaining records
(and splits) to be processed in the same way as above</li>
+ * </ol></p>
+ * <p>Using {@link MailboxExecutor} allows to avoid explicit synchronization.
At most one mail should be enqueued at any
+ * given time.</p>
+ * <p>Using FSM approach allows to explicitly define states and enforce {@link
ReaderState#TRANSITIONS transitions} between them.</p>
*/
@Internal
public class ContinuousFileReaderOperator<OUT> extends
AbstractStreamOperator<OUT>
- implements OneInputStreamOperator<TimestampedFileInputSplit, OUT>,
OutputTypeConfigurable<OUT> {
+ implements OneInputStreamOperator<TimestampedFileInputSplit, OUT>,
OutputTypeConfigurable<OUT>, RunnableWithException {
Review comment:
Instead of implementing `RunnableWithException`, I'd use composition where
you use an anonymous class to forward to your method. Then, you don't leak a
new public method not intended to be called externally.
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