wip: make bundler push, not pull

src/main/java/com/google/api/gax/bundling/PushingBundler.java

@@ -0,0 +1,142 @@
+/*
+ * Copyright 2017, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+package com.google.api.gax.bundling;
+
+import com.google.common.base.Preconditions;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.ReentrantLock;
+import org.joda.time.Duration;
+
+/**
+ * Queues up elements until either a duration of time has passed or any threshold in a given set of
+ * thresholds is breached, and then delivers the elements in a bundle to the consumer.
+ */
+public final class PushingBundler<E> {
+
+  private final Runnable flushRunnable =
+      new Runnable() {
+        @Override
+        public void run() {
+          flush();
+        }
+      };
+
+  private final Duration maxDelay;
+  private final ScheduledExecutorService executor;
+
+  // Invariant:
+  // - lock gates all accesses to members below
+  // - currentOpenBundle and currentAlarmFuture are either both null or both non-null
+  // TODO(pongad): Require that ThresholdBundleReceiver be thread-safe. Then move it out of the lock.
+  private final ReentrantLock lock = new ReentrantLock();
+  private LinkedList<E> currentOpenBundle;
+  private ScheduledFuture<?> currentAlarmFuture;
+  private final ArrayList<BundlingThreshold<E>> thresholds;
+  private final ThresholdBundleReceiver<E> receiver;
+
+  private PushingBundler(
+      Collection<BundlingThreshold<E>> thresholdPrototypes,
+      ScheduledExecutorService executor,
+      Duration maxDelay,
+      ThresholdBundleReceiver<E> receiver) {
+    this.maxDelay = Preconditions.checkNotNull(maxDelay);
+    this.receiver = Preconditions.checkNotNull(receiver);
+    this.executor = Preconditions.checkNotNull(executor);
+
+    this.thresholds = new ArrayList<BundlingThreshold<E>>(thresholdPrototypes);
+    resetThresholds();
+  }
+
+  /**
+   * Immediately make contained elements available to the {@code ThresholdBundleReceiver}.
+   */
+  public void flush() {
+    lock.lock();
+    try {
+      LinkedList<E> bundle = currentOpenBundle;
+      currentOpenBundle = null;
+      if (currentAlarmFuture != null) {
+        currentAlarmFuture.cancel(false);
+        currentAlarmFuture = null;
+      }
+      resetThresholds();
+
+      if (bundle != null && !bundle.isEmpty()) {
+        receiver.processBundle(bundle);
+      }
+    } finally {
+      lock.unlock();
+    }
+  }
+
+  /**
+   * Adds an element to the bundler. If the element causes the collection to go past any of the
+   * thresholds, the bundle will be made available to the {@code ThresholdBundleReceiver}.
+   */
+  public void add(E e) {
+    lock.lock();
+    try {
+      receiver.validateItem(e);
+      if (currentOpenBundle == null) {
+        currentOpenBundle = new LinkedList<E>();
+        currentAlarmFuture =
+            executor.schedule(flushRunnable, maxDelay.getMillis(), TimeUnit.MILLISECONDS);
+      }
+
+      currentOpenBundle.add(e);
+      if (doesReachThreshold(e)) {
+        flush();
+      }
+    } finally {
+      lock.unlock();
+    }
+  }
+
+  private boolean doesReachThreshold(E e) {
+    for (BundlingThreshold threshold : thresholds) {
+      threshold.accumulate(e);
+      if (threshold.isThresholdReached()) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  private void resetThresholds() {
+    for (int i = 0; i < thresholds.size(); i++) {
+      thresholds.set(i, thresholds.get(i).copyWithZeroedValue());
+    }
+  }
+}