content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.master.block;
  
  import alluxio.clock.ManualClock;
  import alluxio.master.CoreMasterContext;
  import alluxio.master.metrics.MetricsMaster;
  import alluxio.resource.LockResource;
  import alluxio.util.executor.ExecutorServiceFactory;
  
  import java.util.concurrent.CountDownLatch;
  
  /**
   * When the writer is writing, issue a signal so other readers/writers know when to start.
   * A {@link CountDownLatch} will be used to pass the signal.
   * Other readers/writers will wait on the signal to execute.
   */
  class SignalBlockMaster extends DefaultBlockMaster {
    CountDownLatch mLatch;
  
    SignalBlockMaster(MetricsMaster metricsMaster,
                      CoreMasterContext masterContext,
                      CountDownLatch readerLatch) {
      super(metricsMaster, masterContext);
      mLatch = readerLatch;
    }
  
    SignalBlockMaster(MetricsMaster mMetricsMaster,
                      CoreMasterContext masterContext,
                      ManualClock clock,
                      ExecutorServiceFactory constantExecutorServiceFactory,
                      CountDownLatch targetLatch) {
      super(mMetricsMaster, masterContext, clock, constantExecutorServiceFactory);
      mLatch = targetLatch;
    }
  
    void setLatch(CountDownLatch newLatch) {
      mLatch = newLatch;
    }
  
    @Override
    LockResource lockBlock(long blockId) {
      LockResource res = super.lockBlock(blockId);
      // The latch can receive more signals than the countdown number
      // But the CountdownLatch guarantees nothing happens if the countdown is already 0
      mLatch.countDown();
      return res;
    }
  }
  