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package net.spy.memcached.transcoders;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;

import net.spy.memcached.CASValue;
import net.spy.memcached.CachedData;
import net.spy.memcached.compat.SpyObject;
import net.spy.memcached.internal.BasicThreadFactory;

/**
 * Asynchronous transcoder.
 */
public class TranscodeService extends SpyObject {

  private final ThreadPoolExecutor pool;

  public TranscodeService(boolean daemon) {
    pool = new ThreadPoolExecutor(1, 10, 60L,
            TimeUnit.MILLISECONDS, new ArrayBlockingQueue(100),
            new BasicThreadFactory("transcoder", daemon),
            new ThreadPoolExecutor.DiscardPolicy());
  }

  /**
   * Perform a decode.
   */
  public  Future decode(final Transcoder tc,
                              final CachedData cachedData) {

    assert !pool.isShutdown() : "Pool has already shut down.";

    TranscodeService.Task task = new TranscodeService.Task(
        new Callable() {
          public T call() {
            return tc.decode(cachedData);
          }
        });

    if (tc.asyncDecode(cachedData)) {
      this.pool.execute(task);
    }
    return task;
  }

  /**
   * Perform a decode.
   */
  public  Future> decode(final Transcoder tc,
                                        final long cas,
                                        final CachedData cachedData) {

    assert !pool.isShutdown() : "Pool has already shut down.";

    TranscodeService.Task> task = new TranscodeService.Task>(
        new Callable>() {
          public CASValue call() {
            return new CASValue(cas, tc.decode(cachedData));
          }
        });

    if (tc.asyncDecode(cachedData)) {
      this.pool.execute(task);
    }
    return task;
  }

  /**
   * Shut down the pool.
   */
  public void shutdown() {
    pool.shutdown();
  }

  /**
   * Ask whether this service has been shut down.
   */
  public boolean isShutdown() {
    return pool.isShutdown();
  }

  private static class Task extends FutureTask {
    private final AtomicBoolean isRunning = new AtomicBoolean(false);

    public Task(Callable callable) {
      super(callable);
    }

    @Override
    public T get() throws InterruptedException, ExecutionException {
      this.run();
      return super.get();
    }

    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException,
            ExecutionException, TimeoutException {
      this.run();
      return super.get(timeout, unit);
    }

    @Override
    public void run() {
      if (this.isRunning.compareAndSet(false, true)) {
        super.run();
      }
    }
  }

}