/*
 * 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;

import alluxio.client.file.FileSystem;

import com.google.common.base.Supplier;

import java.io.Closeable;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import javax.annotation.concurrent.ThreadSafe;

/**
 * Keeps a collection of all clients ({@link FileSystem}) returned. The main reason for this is
 * to build cleanup clients.
 */
@ThreadSafe
public final class ClientPool implements Closeable {
  private final List<FileSystem> mClients =
      Collections.synchronizedList(new ArrayList<FileSystem>());

  ClientPool(Supplier<String> uriSupplier) {}

  /**
   * Returns a {@link FileSystem} client. This client does not need to be
   * closed directly, but can be closed by calling {@link #close()} on this object.
   *
   * @return a {@link FileSystem} client
   */
  public FileSystem getClient() throws IOException {
    final FileSystem fs = FileSystem.Factory.get();
    mClients.add(fs);
    return fs;
  }

  @Override
  public void close() throws IOException {
    synchronized (mClients) {
      mClients.clear();
    }
  }
}