pkuwm commented on a change in pull request #741: Fix ConcurrentModification
exception in Workflow Garbage Collection
URL: https://github.com/apache/helix/pull/741#discussion_r383095382
##########
File path: helix-core/src/main/java/org/apache/helix/task/TaskUtil.java
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@@ -1043,23 +1043,40 @@ public static void purgeExpiredJobs(String workflow,
WorkflowConfig workflowConf
* @param dataProvider
* @param manager
*/
- public static void workflowGarbageCollection(WorkflowControllerDataProvider
dataProvider,
+ public static void workflowGarbageCollection(final
WorkflowControllerDataProvider dataProvider,
final HelixManager manager) {
// Garbage collections for conditions where workflow context exists but
config is missing.
- Map<String, ZNRecord> contexts = dataProvider.getContexts();
- HelixDataAccessor accessor = manager.getHelixDataAccessor();
- HelixPropertyStore<ZNRecord> propertyStore =
manager.getHelixPropertyStore();
+ Set<String> existingContexts;
+ /*
+ * Here try-catch is used to avoid concurrent modification exception while
doing deep copy.
+ * Map.keySet() can produce concurrent modification exception.
+ * Reason: If the map is modified while an iteration over the set is in
progress, concurrent
+ * modification exception will be thrown.
+ */
+ try {
+ existingContexts = new HashSet<>(dataProvider.getContexts().keySet());
Review comment:
@alirezazamani Is there a specific reason why we don't change the contexts
map below to a concurrent hash map and make it thread safe?
```
private Map<String, ZNRecord> _contextMap = new HashMap<>();
```
What I can only see is performance concern when contexts modification is
blocked by this copying. If performance is not that bad, I believe changing the
contextMap to a concurrent hash map is the right fix.
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