alirezazamani commented on a change in pull request #741: Fix
ConcurrentModification exception in Workflow Garbage Collection
URL: https://github.com/apache/helix/pull/741#discussion_r377436725
##########
File path: helix-core/src/main/java/org/apache/helix/task/TaskUtil.java
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@@ -1043,23 +1043,33 @@ 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();
+ // toBeDeletedWorkflows is a set that contains the name of the workflows
that their contexts
+ // should be deleted.
Set<String> toBeDeletedWorkflows = new HashSet<>();
- for (Map.Entry<String, ZNRecord> entry : contexts.entrySet()) {
- if (entry.getValue() != null
- && entry.getValue().getId().equals(TaskUtil.WORKFLOW_CONTEXT_KW)) {
- if (dataProvider.getWorkflowConfig(entry.getKey()) == null) {
- toBeDeletedWorkflows.add(entry.getKey());
+ try {
+ Set<String> existingWorkflowContexts = new
HashSet<>(dataProvider.getContexts().keySet());
+ for (String entry : existingWorkflowContexts) {
+ if (entry != null) {
+ WorkflowConfig cfg = dataProvider.getWorkflowConfig(entry);
+ WorkflowContext ctx = dataProvider.getWorkflowContext(entry);
+ if (ctx != null && ctx.getId().equals(TaskUtil.WORKFLOW_CONTEXT_KW)
&& cfg == null) {
+ toBeDeletedWorkflows.add(entry);
+ }
}
}
+ } catch (Exception e) {
+ LOG.warn(
+ "Exception occurred while creating a list of all existing contexts
with missing config!",
+ e);
}
Review comment:
I don't believe deep copy by itself helps. The code generate concurrent
modification in this function: **map.keySet().** We cannot avoid this. How you
are proposing to get the keys in the map in this scenario? We need to get the
keys no matter what (even for doing deep copy). Even the implementation of deep
copying involves to loop over the elements and copy them one by one to the new
map. A deep copy is merely done by iterating through the elements (keys and
values) and cloning those too. Right? In this case if original map has been
changed while copy operation is happening, we might still get concurrent
modification exception.
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