[jira] [Commented] (SOLR-8323) Add CollectionWatcher API to ZkStateReader

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SOLR-8323?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15267144#comment-15267144 ] 

ASF GitHub Bot commented on SOLR-8323:
--------------------------------------

Github user romseygeek commented on a diff in the pull request:

    https://github.com/apache/lucene-solr/pull/32#discussion_r61777874
  
    --- 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 --
    
    Yeah, I think this can be done in a follow-up issue, if need be?


> Add CollectionWatcher API to ZkStateReader
> ------------------------------------------
>
>                 Key: SOLR-8323
>                 URL: https://issues.apache.org/jira/browse/SOLR-8323
>             Project: Solr
>          Issue Type: Improvement
>    Affects Versions: master
>            Reporter: Alan Woodward
>            Assignee: Alan Woodward
>         Attachments: SOLR-8323.patch, SOLR-8323.patch, SOLR-8323.patch, SOLR-8323.patch
>
>
> An API to watch for changes to collection state would be a generally useful thing, both internally and for client use.



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