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Apache Geode provides a database-like consistency model, reliable transaction processing and a shared-nothing architecture to maintain very low latency performance with high concurrency processing
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/*
 * 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.geode.internal.cache.partitioned.rebalance;

import java.util.Map;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

import org.apache.geode.CancelException;
import org.apache.geode.cache.RegionDestroyedException;
import org.apache.geode.distributed.internal.membership.InternalDistributedMember;

/**
 * A bucket operator that will perform operations on a bucket asynchronously.
 * 
 * This class wraps a delegate bucket operator that is synchronous. That is, the delegate bucket
 * operator is expected to move the bucket and notify the Completion within the scope of the call to
 * create bucket.
 * 
 * What this class does in make that call asynchronous. A task to create the bucket is handed to the
 * thread pool and executed there. After it is done, the completion is notified.
 * 
 * Calling waitForOperations waits for all previously submitted operations and ensures the
 * completions are notified.
 * 
 * Note that only createRedundantBucket is asynchronous, the rest of the operations are synchronous.
 * 
 */
public class ParallelBucketOperator implements BucketOperator {

  private final BucketOperator delegate;
  private final ExecutorService executor;
  private final Semaphore operationSemaphore;
  private final int maxParallelOperations;
  private final ConcurrentLinkedQueue pendingSuccess =
      new ConcurrentLinkedQueue();
  private final ConcurrentLinkedQueue pendingFailure =
      new ConcurrentLinkedQueue();


  /**
   * Create a parallel bucket operator
   * 
   * @param maxParallelOperations The number of operations that can execute concurrently. Futher
   *        calls to createRedundantBucket will block.
   * @param executor the executor to submit tasks to. This executor should be able to create at
   *        least maxParallelOperations threads.
   * @param operator A bucket operator that is synchronous that will do the actual work of creating
   *        a bucket.
   */
  public ParallelBucketOperator(int maxParallelOperations, ExecutorService executor,
      BucketOperator operator) {
    this.maxParallelOperations = maxParallelOperations;
    this.operationSemaphore = new Semaphore(maxParallelOperations);
    this.delegate = operator;
    this.executor = executor;
  }

  /**
   * Create a redundant bucket asynchronously. If maxParallelOperations is not reached, this call
   * will submit a task and return immediately. Otherwise, it will block until an executor thread is
   * available to take a task.
   * 
   * The completion will not be notified until the caller makes another call to createRedundant
   * bucket or waitForOperations.
   */
  @Override
  public void createRedundantBucket(final InternalDistributedMember targetMember,
      final int bucketId, final Map colocatedRegionBytes,
      final Completion completion) {
    drainCompletions();
    operationSemaphore.acquireUninterruptibly();
    executor.execute(new Runnable() {
      @Override
      public void run() {
        try {
          delegate.createRedundantBucket(targetMember, bucketId, colocatedRegionBytes,
              new Completion() {
                @Override
                public void onSuccess() {
                  pendingSuccess.add(completion);
                }

                @Override
                public void onFailure() {
                  pendingFailure.add(completion);
                }
              });
        } catch (CancelException e) {
          // ignore
        } catch (RegionDestroyedException e) {
          // ignore
        } finally {
          operationSemaphore.release();
        }
      }
    });

  }

  @Override
  public boolean removeBucket(InternalDistributedMember memberId, int id,
      Map colocatedRegionSizes) {
    return delegate.removeBucket(memberId, id, colocatedRegionSizes);
  }

  @Override
  public boolean moveBucket(InternalDistributedMember sourceMember,
      InternalDistributedMember targetMember, int bucketId,
      Map colocatedRegionBytes) {
    return delegate.moveBucket(sourceMember, targetMember, bucketId, colocatedRegionBytes);
  }

  @Override
  public boolean movePrimary(InternalDistributedMember source, InternalDistributedMember target,
      int bucketId) {
    return delegate.movePrimary(source, target, bucketId);
  }

  public void drainCompletions() {
    Completion next = null;
    while ((next = pendingSuccess.poll()) != null) {
      next.onSuccess();
    }

    while ((next = pendingFailure.poll()) != null) {
      next.onFailure();
    }

  }

  /**
   * Wait for any pending operations, and notify the the completions that the operations and done.
   */
  public void waitForOperations() {
    boolean interrupted = false;
    while (!executor.isShutdown()) {
      try {
        if (operationSemaphore.tryAcquire(maxParallelOperations, 1, TimeUnit.SECONDS)) {
          operationSemaphore.release(maxParallelOperations);

          drainCompletions();

          if (interrupted) {
            Thread.currentThread().interrupt();
          }

          return;
        }
      } catch (InterruptedException e) {
        interrupted = true;
      }
    }
  }

}