{"action":"created","comment":{"url":"https://api.github.com/repos/druid-io/druid/pulls/comments/72312623","id":72312623,"diff_hunk":"@@ -0,0 +1,135 @@\n+/*\n+ * Licensed to Metamarkets Group Inc. (Metamarkets) under one\n+ * or more contributor license agreements. See the NOTICE file\n+ * distributed with this work for additional information\n+ * regarding copyright ownership. Metamarkets licenses this file\n+ * to you under the Apache License, Version 2.0 (the\n+ * \"License\"); you may not use this file except in compliance\n+ * with the License. You may obtain a copy of the License at\n+ *\n+ * http://www.apache.org/licenses/LICENSE-2.0\n+ *\n+ * Unless required by applicable law or agreed to in writing,\n+ * software distributed under the License is distributed on an\n+ * \"AS IS\" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY\n+ * KIND, either express or implied. See the License for the\n+ * specific language governing permissions and limitations\n+ * under the License.\n+ */\n+\n+package io.druid.collections;\n+\n+import com.metamx.common.ISE;\n+import com.metamx.common.logger.Logger;\n+\n+import java.io.Closeable;\n+import java.util.concurrent.atomic.AtomicBoolean;\n+\n+public class ReferenceCountingResourceHolder<T> implements ResourceHolder<T>\n+{\n+  private static final Logger log = new Logger(ReferenceCountingResourceHolder.class);\n+\n+  private final Object lock = new Object();\n+  private final T object;\n+  private final Closeable closer;\n+\n+  private long refcount = 1;\n+  private boolean didClose = false;\n+\n+  public ReferenceCountingResourceHolder(final T object, final Closeable closer)\n+  {\n+    this.object = object;\n+    this.closer = closer;\n+  }\n+\n+  @Override\n+  public T get()\n+  {\n+    synchronized (lock) {\n+      if (refcount <= 0) {\n+        throw new ISE(\"Already closed!\");\n+      }\n+\n+      return object;\n+    }\n+  }\n+\n+  public ReferenceCountingResourceHolder.Releaser increment()\n+  {\n+    synchronized (lock) {\n+      if (refcount <= 0) {\n+        throw new ISE(\"Already closed!\");\n+      }\n+\n+      refcount++;\n+\n+      final AtomicBoolean didRelease = new AtomicBoolean();\n+      return new Releaser()\n+      {\n+        @Override\n+        public void release()\n+        {\n+          if (didRelease.compareAndSet(false, true)) {\n+            decrement();\n+          } else {\n+            log.warn(\"WTF?! release called but we are already released!\");\n+          }\n+        }\n+\n+        @Override\n+        protected void finalize() throws Throwable\n+        {\n+          if (didRelease.compareAndSet(false, true)) {\n+            log.warn(\"Not released! Object was[%s], releasing on finalize of releaser.\", object);\n+            decrement();\n+          }\n+        }\n+      };\n+    }\n+  }\n+\n+  @Override\n+  public void close()\n+  {\n+    synchronized (lock) {\n+      if (!didClose) {\n+        didClose = true;\n+        decrement();\n+      } else {\n+        log.warn(new ISE(\"Already closed!\"), \"Already closed\");\n+      }\n+    }\n+  }\n+\n+  @Override\n+  protected void finalize() throws Throwable\n+  {\n+    synchronized (lock) {\n+      if (!didClose) {\n+        log.warn(\"Not closed! Object was[%s], closing on finalize of holder.\", object);\n+        didClose = true;\n+        decrement();\n+      }\n+    }\n+  }\n+\n+  private void decrement()\n+  {\n+    synchronized (lock) {\n+      refcount--;\n+      if (refcount <= 0) {\n+        try {\n+          closer.close();\n+        }\n+        catch (Exception e) {\n+          log.error(e, \"WTF?! Close failed, uh oh...\");\n+        }\n+      }\n+    }\n+  }\n+\n+  public interface Releaser","path":"common/src/main/java/io/druid/collections/ReferenceCountingResourceHolder.java","position":131,"original_position":131,"commit_id":"646d35d81cae6caf28a38e89d9cdf2a45825cdcb","original_commit_id":"646d35d81cae6caf28a38e89d9cdf2a45825cdcb","user":{"login":"gianm","id":1214075,"avatar_url":"https://avatars.githubusercontent.com/u/1214075?v=3","gravatar_id":"","url":"https://api.github.com/users/gianm","html_url":"https://github.com/gianm","followers_url":"https://api.github.com/users/gianm/followers","following_url":"https://api.github.com/users/gianm/following{/other_user}","gists_url":"https://api.github.com/users/gianm/gists{/gist_id}","starred_url":"https://api.github.com/users/gianm/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/gianm/subscriptions","organizations_url":"https://api.github.com/users/gianm/orgs","repos_url":"https://api.github.com/users/gianm/repos","events_url":"https://api.github.com/users/gianm/events{/privacy}","received_events_url":"https://api.github.com/users/gianm/received_events","type":"User","site_admin":false},"body":"Hmm, it can extend Closeable though (and drop the throws clause). I'll change that.","created_at":"2016-07-26T18:47:04Z","updated_at":"2016-07-26T18:47:04Z","html_url":"https://github.com/druid-io/druid/pull/3268#discussion_r72312623","pull_request_url":"https://api.github.com/repos/druid-io/druid/pulls/3268","_links":{"self":{"href":"https://api.github.com/repos/druid-io/druid/pulls/comments/72312623"},"html":{"href":"https://github.com/druid-io/druid/pull/3268#discussion_r72312623"},"pull_request":{"href":"https://api.github.com/repos/druid-io/druid/pulls/3268"}}},"pull_request":{"url":"https://api.github.com/repos/druid-io/druid/pulls/3268","id":78203327,"html_url":"https://github.com/druid-io/druid/pull/3268","diff_url":"https://github.com/druid-io/druid/pull/3268.diff","patch_url":"https://github.com/druid-io/druid/pull/3268.patch","issue_url":"https://api.github.com/repos/druid-io/druid/issues/3268","number":3268,"state":"open","locked":false,"title":"Reference counting, better error handling for resources in groupBy v2.","user":{"login":"gianm","id":1214075,"avatar_url":"https://avatars.githubusercontent.com/u/1214075?v=3","gravatar_id":"","url":"https://api.github.com/users/gianm","html_url":"https://github.com/gianm","followers_url":"https://api.github.com/users/gianm/followers","following_url":"https://api.github.com/users/gianm/following{/other_user}","gists_url":"https://api.github.com/users/gianm/gists{/gist_id}","starred_url":"https://api.github.com/users/gianm/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/gianm/subscriptions","organizations_url":"https://api.github.com/users/gianm/orgs","repos_url":"https://api.github.com/users/gianm/repos","events_url":"https://api.github.com/users/gianm/events{/privacy}","received_events_url":"https://api.github.com/users/gianm/received_events","type":"User","site_admin":false},"body":"Refcounting prevents releasing the merge buffer, or closing the concurrent\r\ngrouper, before the processing threads have all finished.\r\n\r\nThe better error handling prevents an avalanche of per-runner exceptions\r\nwhen grouping resources are exhausted, by grouping those all up into a\r\nsingle merged 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