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/*
 * Licensed to the University of California, Berkeley 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 tachyon.client.file;

import tachyon.client.ClientContext;
import tachyon.client.FileSystemMasterClient;
import tachyon.client.block.TachyonBlockStore;

/**
 * A shared context in each client JVM for common File System client functionality such as a pool
 * of master clients. This class is thread safe.
 */
public enum FileSystemContext {
  INSTANCE;

  private FileSystemMasterClientPool mFileSystemMasterClientPool;
  private final TachyonBlockStore mTachyonBlockStore;

  /**
   * Creates a new file stream context.
   */
  FileSystemContext() {
    mFileSystemMasterClientPool =
        new FileSystemMasterClientPool(ClientContext.getMasterAddress());
    mTachyonBlockStore = TachyonBlockStore.get();
  }

  /**
   * Acquires a block master client from the block master client pool.
   *
   * @return the acquired block master client
   */
  public FileSystemMasterClient acquireMasterClient() {
    return mFileSystemMasterClientPool.acquire();
  }

  /**
   * Releases a block master client into the block master client pool.
   *
   * NOTE: the client pool is already thread-safe. Synchronizing on FileSystemContext will lead to
   * deadlock: thread A acquired a client and awaits for FileSystemContext to release the client,
   * while thread B holds the lock of FileSystemContext but waits for available clients.
   *
   * @param masterClient a block master client to release
   */
  public void releaseMasterClient(FileSystemMasterClient masterClient) {
    mFileSystemMasterClientPool.release(masterClient);
  }

  /**
   * @return the Tachyon block store
   */
  public synchronized TachyonBlockStore getTachyonBlockStore() {
    return mTachyonBlockStore;
  }

  /**
   * Re-initializes the Block Store context. This method should only be used in
   * {@link ClientContext}.
   */
  public synchronized void reset() {
    mFileSystemMasterClientPool.close();
    mFileSystemMasterClientPool =
        new FileSystemMasterClientPool(ClientContext.getMasterAddress());
  }
}