Github user dragonsinth commented on a diff in the pull request: https://github.com/apache/lucene-solr/pull/32#discussion_r61643539 --- Diff: solr/solrj/src/java/org/apache/solr/common/cloud/ZkStateReader.java --- @@ -1066,32 +1079,201 @@ public static String getCollectionPath(String coll) { return COLLECTIONS_ZKNODE+"/"+coll + "/state.json"; } - public void addCollectionWatch(String coll) { - if (interestingCollections.add(coll)) { - LOG.info("addZkWatch [{}]", coll); - new StateWatcher(coll).refreshAndWatch(false); + /** + * Notify this reader that a local Core is a member of a collection, and so that collection + * state should be watched. + * + * Not a public API. This method should only be called from ZkController. + * + * The number of cores per-collection is tracked, and adding multiple cores from the same + * collection does not increase the number of watches. + * + * @param collection the collection that the core is a member of + * + * @see ZkStateReader#unregisterCore(String) + */ + public void registerCore(String collection) { + AtomicBoolean reconstructState = new AtomicBoolean(false); + collectionWatches.compute(collection, (k, v) -> { + if (v == null) { + reconstructState.set(true); + v = new CollectionWatch(); + } + v.coreRefCount++; + return v; + }); + if (reconstructState.get()) { + new StateWatcher(collection).refreshAndWatch(); + synchronized (getUpdateLock()) { + constructState(); + } + } + } + + /** + * Notify this reader that a local core that is a member of a collection has been closed. + * + * Not a public API. This method should only be called from ZkController. + * + * If no cores are registered for a collection, and there are no {@link CollectionStateWatcher}s + * for that collection either, the collection watch will be removed. + * + * @param collection the collection that the core belongs to + */ + public void unregisterCore(String collection) { + AtomicBoolean reconstructState = new AtomicBoolean(false); + collectionWatches.compute(collection, (k, v) -> { + if (v == null) + return null; + if (v.coreRefCount > 0) + v.coreRefCount--; + if (v.canBeRemoved()) { + watchedCollectionStates.remove(collection); + lazyCollectionStates.put(collection, new LazyCollectionRef(collection)); + reconstructState.set(true); + return null; + } + return v; + }); + if (reconstructState.get()) { + synchronized (getUpdateLock()) { + constructState(); + } + } + } + + /** + * Register a CollectionStateWatcher to be called when the state of a collection changes + * + * A given CollectionStateWatcher will be only called once. If you want to have a persistent watcher, + * it should register itself again in its {@link CollectionStateWatcher#onStateChanged(Set, DocCollection)} + * method. + */ + public void registerCollectionStateWatcher(String collection, CollectionStateWatcher stateWatcher) { + AtomicBoolean watchSet = new AtomicBoolean(false); + collectionWatches.compute(collection, (k, v) -> { + if (v == null) { + v = new CollectionWatch(); + watchSet.set(true); + } + v.stateWatchers.add(stateWatcher); + return v; + }); + if (watchSet.get()) { + new StateWatcher(collection).refreshAndWatch(); synchronized (getUpdateLock()) { constructState(); } } } + /** + * Block until a CollectionStatePredicate returns true, or the wait times out + * + * Note that the predicate may be called again even after it has returned true, so + * implementors should avoid changing state within the predicate call itself. --- End diff -- It seems like it would be nice to shield callers from doing any kind of similar mutexing. If you don't want to bother right now, I can come back and see if I can do something not yucky looking here.
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