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Subject [GitHub] [incubator-zipkin] Logic-32 commented on a change in pull request #2502: Adding storage-throttle module to address "over capacity" issues
Date Tue, 30 Apr 2019 16:32:24 GMT
Logic-32 commented on a change in pull request #2502: Adding storage-throttle module to address
"over capacity" issues
URL: https://github.com/apache/incubator-zipkin/pull/2502#discussion_r279835441
 
 

 ##########
 File path: zipkin-server/src/main/java/zipkin2/server/internal/throttle/ThrottledCall.java
 ##########
 @@ -0,0 +1,211 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package zipkin2.server.internal.throttle;
+
+import com.netflix.concurrency.limits.Limiter;
+import com.netflix.concurrency.limits.Limiter.Listener;
+import java.io.IOException;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.function.Supplier;
+import zipkin2.Call;
+import zipkin2.Callback;
+import zipkin2.storage.InMemoryStorage;
+
+/**
+ * {@link Call} implementation that is backed by an {@link ExecutorService}. The ExecutorService
serves two
+ * purposes:
+ * <ol>
+ * <li>Limits the number of requests that can run in parallel.</li>
+ * <li>Depending on configuration, can queue up requests to make sure we don't aggressively
drop requests that would
+ *     otherwise succeed if given a moment. Bounded queues are safest for this as unbounded
ones can lead to heap
+ *     exhaustion and {@link OutOfMemoryError OOM errors}.</li>
+ * </ol>
+ *
+ * @see ThrottledStorageComponent
+ */
+class ThrottledCall<V> extends Call<V> {
+  private final ExecutorService executor;
+  private final Limiter<Void> limiter;
+  private final Listener limitListener;
+  /**
+   * Delegate call needs to be supplied later to avoid having it take action when it is created
(like
+   * {@link InMemoryStorage} and thus avoid being throttled.
+   */
+  private final Supplier<Call<V>> delegate;
+  private Call<V> call;
+  private boolean canceled;
+
+  public ThrottledCall(ExecutorService executor, Limiter<Void> limiter, Supplier<Call<V>>
delegate) {
+    this.executor = executor;
+    this.limiter = limiter;
+    this.limitListener = limiter.acquire(null).orElseThrow(RejectedExecutionException::new);
+    this.delegate = delegate;
+  }
+
+  private ThrottledCall(ThrottledCall other) {
+    this(other.executor, other.limiter, other.call == null ? other.delegate : () -> other.call.clone());
+  }
+
+  @Override
+  public V execute() throws IOException {
+    try {
+      call = delegate.get();
+
+      // Make sure we throttle
+      Future<V> future = executor.submit(() -> {
+        try (AutoCloseable nameReverter = updateThreadName(call.toString())) {
+          return call.execute();
+        }
+      });
+      V result = future.get(); // Still block for the response
+
+      limitListener.onSuccess();
+      return result;
+    } catch (ExecutionException e) {
+      Throwable cause = e.getCause();
+      if (cause instanceof RejectedExecutionException) {
+        // Storage rejected us, throttle back
+        limitListener.onDropped();
+      } else {
+        limitListener.onIgnore();
+      }
+
+      throw new ThrottleException(cause);
 
 Review comment:
   Per my comment on line 95, I updated this to check the type of `cause` and only wrap when
necessary in this specific instance.

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