gianm commented on code in PR #19496:
URL: https://github.com/apache/druid/pull/19496#discussion_r3291937123
##########
processing/src/main/java/org/apache/druid/segment/file/PartialSegmentFileMapperV10.java:
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@@ -507,6 +517,15 @@ public void initializeContainer(int containerIndex) throws
IOException
* {@link #mapFile} calls for files in this container will re-trigger
downloads via {@link #initializeContainer}
* and the bitmap will be repopulated incrementally.
* <p>
+ * <b>Concurrency contract.</b> The caller is responsible for ensuring no
concurrent {@link #mapFile} (or
+ * {@link #ensureFilesAvailable}) call is in flight for any file in this
container. This is enforced one layer up
+ * by the cache-entry refcount: {@code PartialSegmentBundleCacheEntry} only
invokes {@code evictContainer} from its
+ * {@code doActualUnmount} callback, which fires only after every reference
acquired via
+ * {@code acquireReference()} has been closed. Bypassing that gate is
dangerous — {@link ByteBufferUtils#unmap}
Review Comment:
I am approving this PR but wouldn't mind if this comment was tidied up a bit
prior to merge. It's a bit verbose.
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