exec/java-exec/src/main/java/org/apache/drill/exec/ops/SendingAccountor.java

/*
 * 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 org.apache.drill.exec.ops;

import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicInteger;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * Account for whether all messages sent have been completed. Necessary before
 * finishing a task so we don't think buffers are hanging when they will be
 * released.
 *
 * TODO: Need to update to use long for number of pending messages.
 */
public class SendingAccountor {
  private static final Logger logger = LoggerFactory.getLogger(SendingAccountor.class);

  private final AtomicInteger batchesSent = new AtomicInteger(0);
  private final Semaphore wait = new Semaphore(0);

  void increment() {
    batchesSent.incrementAndGet();
  }

  void decrement() {
    wait.release();
  }

  public synchronized void waitForSendComplete() {
      int waitForBatches = batchesSent.get();
      boolean isInterrupted = false;
      while(waitForBatches != 0) {
        try {
          wait.acquire(waitForBatches);
          waitForBatches = batchesSent.addAndGet(-1 * waitForBatches);
        } catch (InterruptedException e) {
          // We should always wait for send complete. If we don't, we'll leak memory or have a memory miss when we try
          // to send. This should be safe because: network connections should get disconnected and fail a send if a
          // node goes down, otherwise, the receiving side connection should always consume from the rpc layer
          // (blocking is cooperative and will get triggered before this)
          logger.warn("Interrupted while waiting for send complete. Continuing to wait.", e);

          isInterrupted = true;
        }
      }

      if (isInterrupted) {
        // Preserve evidence that the interruption occurred so that code higher up on the call stack can learn of the
        // interruption and respond to it if it wants to.
        Thread.currentThread().interrupt();
      }
  }
}