leventov commented on a change in pull request #8236: Add TaskResourceCleaner;
fix a couple of concurrency bugs in batch tasks
URL: https://github.com/apache/incubator-druid/pull/8236#discussion_r311237120
##########
File path:
indexing-service/src/main/java/org/apache/druid/indexing/common/task/CompactionTask.java
##########
@@ -146,10 +146,13 @@
private final RetryPolicyFactory retryPolicyFactory;
@JsonIgnore
- private List<IndexTask> indexTaskSpecs;
+ private final AppenderatorsManager appenderatorsManager;
@JsonIgnore
- private AppenderatorsManager appenderatorsManager;
+ private List<IndexTask> indexTaskSpecs;
+
+ @Nullable
+ private volatile IndexTask currentRunningTaskSpec = null;
Review comment:
But first of all, "This variable is updated by the main thread and read by
an HTTP thread when `{@link #stopGracefully}` is called." doesn't explain the
concurrency model in enough detail. Can `{@link #stopGracefully}` be called
fully concurrently at whatever moment in parallel with `runTask()`, or it could
be called only in response to some failure within `runTask()`, just from a
different thread? In the first case, `volatile` is likely needed to ensure
*safe publication* (see JCIP 3.5, or
[here](https://shipilev.net/blog/2014/safe-public-construction/#_safe_publication))
of the `IndexTask` object. In the second case, volatile is almost definitely
redundant, if the thread from which `stopGracefully()` is called "gets
informed" about the failure in `runTask()` in any way that is different from
something like a spin-loop read of a non-volatile field (yes, this is very
obscure and never actually happens in practice).
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