jihoonson commented on a change in pull request #6041: Synchronize scheduled
poll() calls in SQLMetadataSegmentManager
URL: https://github.com/apache/incubator-druid/pull/6041#discussion_r204953651
##########
File path:
server/src/main/java/io/druid/metadata/SQLMetadataSegmentManager.java
##########
@@ -96,9 +94,18 @@
private final AtomicReference<ConcurrentHashMap<String, DruidDataSource>>
dataSourcesRef;
private final SQLMetadataConnector connector;
- private volatile ListeningScheduledExecutorService exec = null;
- private volatile ListenableFuture<?> future = null;
- private volatile boolean started;
+ /** The number of times this SQLMetadataSegmentManager was started. */
+ private long startCount = 0;
+ /**
+ * Equal to the current {@link #startCount} value, if the
SQLMetadataSegmentManager is currently started; -1 if
+ * currently stopped.
+ *
+ * This field is used to implement a simple stamp mechanism instead of just
a boolean "started" flag to prevent
+ * the theoretical situation of two tasks scheduled in {@link #start()}
calling {@link #poll()} concurrently, if
+ * the sequence of {@link #start()} - {@link #stop()} - {@link #start()}
actions occurs quickly.
+ */
Review comment:
Sounds a good convention. I also haven't noticed until I check the changes
in https://github.com/apache/incubator-druid/pull/5554 which introduced this
bug.
Added a comment.
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
With regards,
Apache Git Services
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
