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Java example source code file (AbstractFutureBenchmarks.java)

This example Java source code file (AbstractFutureBenchmarks.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

annotation, cancellationexception, cancelled, canignorereturnvalue, completed, executionexception, facade, interrupted, interruptedexception, oldabstractfuture, override, sync, threading, threads, throwable, timeoutexception

The AbstractFutureBenchmarks.java Java example source code

/*
 * Copyright (C) 2014 The Guava Authors
 *
 * Licensed 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 com.google.common.util.concurrent;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.util.concurrent.CancellationException;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;

import javax.annotation.Nullable;

/**
 * Utilities for the AbstractFutureBenchmarks
 */
final class AbstractFutureBenchmarks {
  private AbstractFutureBenchmarks() {}

  interface Facade<T> extends ListenableFuture {
    @CanIgnoreReturnValue
    boolean set(T t);

    @CanIgnoreReturnValue
    boolean setException(Throwable t);
  }

  private static class NewAbstractFutureFacade<T> extends AbstractFuture implements Facade {
    @CanIgnoreReturnValue
    @Override
    public boolean set(T t) {
      return super.set(t);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean setException(Throwable t) {
      return super.setException(t);
    }
  }

  private static class OldAbstractFutureFacade<T>
      extends OldAbstractFuture<T> implements Facade {
    @CanIgnoreReturnValue
    @Override
    public boolean set(T t) {
      return super.set(t);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean setException(Throwable t) {
      return super.setException(t);
    }
  }

  enum Impl {
    NEW {
      @Override <T> Facade newFacade() {
        return new NewAbstractFutureFacade<T>();
      }
    },
    OLD {
      @Override <T> Facade newFacade() {
        return new OldAbstractFutureFacade<T>();
      }
    };

    abstract <T> Facade newFacade();
  }

  static void awaitWaiting(Thread t) {
    while (true) {
      Thread.State state = t.getState();
      switch (state) {
        case RUNNABLE:
        case BLOCKED:
          Thread.yield();
          break;
        case WAITING:
          return;
        default:
          throw new AssertionError("unexpected state: " + state);
      }
    }
  }

  abstract static class OldAbstractFuture<V> implements ListenableFuture {

    /** Synchronization control for AbstractFutures. */
    private final Sync<V> sync = new Sync();

    // The execution list to hold our executors.
    private final ExecutionList executionList = new ExecutionList();

    /**
     * Constructor for use by subclasses.
     */
    protected OldAbstractFuture() {}

    /*
     * Improve the documentation of when InterruptedException is thrown. Our
     * behavior matches the JDK's, but the JDK's documentation is misleading.
     */
    /**
     * {@inheritDoc}
     *
     * <p>The default {@link AbstractFuture} implementation throws {@code
     * InterruptedException} if the current thread is interrupted before or during
     * the call, even if the value is already available.
     *
     * @throws InterruptedException if the current thread was interrupted before
     *     or during the call (optional but recommended).
     * @throws CancellationException {@inheritDoc}
     */
    @CanIgnoreReturnValue
    @Override
    public V get(long timeout, TimeUnit unit)
        throws InterruptedException, TimeoutException, ExecutionException {
      return sync.get(unit.toNanos(timeout));
    }

    /*
     * Improve the documentation of when InterruptedException is thrown. Our
     * behavior matches the JDK's, but the JDK's documentation is misleading.
     */
    /**
     * {@inheritDoc}
     *
     * <p>The default {@link AbstractFuture} implementation throws {@code
     * InterruptedException} if the current thread is interrupted before or during
     * the call, even if the value is already available.
     *
     * @throws InterruptedException if the current thread was interrupted before
     *     or during the call (optional but recommended).
     * @throws CancellationException {@inheritDoc}
     */
    @CanIgnoreReturnValue
    @Override
    public V get() throws InterruptedException, ExecutionException {
      return sync.get();
    }

    @Override
    public boolean isDone() {
      return sync.isDone();
    }

    @Override
    public boolean isCancelled() {
      return sync.isCancelled();
    }

    @CanIgnoreReturnValue
    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
      if (!sync.cancel(mayInterruptIfRunning)) {
        return false;
      }
      executionList.execute();
      if (mayInterruptIfRunning) {
        interruptTask();
      }
      return true;
    }

    /**
     * Subclasses can override this method to implement interruption of the
     * future's computation. The method is invoked automatically by a successful
     * call to {@link #cancel(boolean) cancel(true)}.
     *
     * <p>The default implementation does nothing.
     *
     * @since 10.0
     */
    protected void interruptTask() {
    }

    /**
     * Returns true if this future was cancelled with {@code
     * mayInterruptIfRunning} set to {@code true}.
     *
     * @since 14.0
     */
    protected final boolean wasInterrupted() {
      return sync.wasInterrupted();
    }

    /**
     * {@inheritDoc}
     *
     * @since 10.0
     */
    @Override
    public void addListener(Runnable listener, Executor exec) {
      executionList.add(listener, exec);
    }

    /**
     * Subclasses should invoke this method to set the result of the computation
     * to {@code value}.  This will set the state of the future to
     * {@link OldAbstractFuture.Sync#COMPLETED} and invoke the listeners if the
     * state was successfully changed.
     *
     * @param value the value that was the result of the task.
     * @return true if the state was successfully changed.
     */
    @CanIgnoreReturnValue
    protected boolean set(@Nullable V value) {
      boolean result = sync.set(value);
      if (result) {
        executionList.execute();
      }
      return result;
    }

    /**
     * Subclasses should invoke this method to set the result of the computation
     * to an error, {@code throwable}.  This will set the state of the future to
     * {@link OldAbstractFuture.Sync#COMPLETED} and invoke the listeners if the
     * state was successfully changed.
     *
     * @param throwable the exception that the task failed with.
     * @return true if the state was successfully changed.
     */
    @CanIgnoreReturnValue
    protected boolean setException(Throwable throwable) {
      boolean result = sync.setException(checkNotNull(throwable));
      if (result) {
        executionList.execute();
      }
      return result;
    }

    /**
     * <p>Following the contract of {@link AbstractQueuedSynchronizer} we create a
     * private subclass to hold the synchronizer.  This synchronizer is used to
     * implement the blocking and waiting calls as well as to handle state changes
     * in a thread-safe manner.  The current state of the future is held in the
     * Sync state, and the lock is released whenever the state changes to
     * {@link #COMPLETED}, {@link #CANCELLED}, or {@link #INTERRUPTED}
     *
     * <p>To avoid races between threads doing release and acquire, we transition
     * to the final state in two steps.  One thread will successfully CAS from
     * RUNNING to COMPLETING, that thread will then set the result of the
     * computation, and only then transition to COMPLETED, CANCELLED, or
     * INTERRUPTED.
     *
     * <p>We don't use the integer argument passed between acquire methods so we
     * pass around a -1 everywhere.
     */
    static final class Sync<V> extends AbstractQueuedSynchronizer {

      private static final long serialVersionUID = 0L;

      /* Valid states. */
      static final int RUNNING = 0;
      static final int COMPLETING = 1;
      static final int COMPLETED = 2;
      static final int CANCELLED = 4;
      static final int INTERRUPTED = 8;

      private V value;
      private Throwable exception;

      /*
       * Acquisition succeeds if the future is done, otherwise it fails.
       */
      @Override
      protected int tryAcquireShared(int ignored) {
        if (isDone()) {
          return 1;
        }
        return -1;
      }

      /*
       * We always allow a release to go through, this means the state has been
       * successfully changed and the result is available.
       */
      @Override
      protected boolean tryReleaseShared(int finalState) {
        setState(finalState);
        return true;
      }

      /**
       * Blocks until the task is complete or the timeout expires.  Throws a
       * {@link TimeoutException} if the timer expires, otherwise behaves like
       * {@link #get()}.
       */
      V get(long nanos) throws TimeoutException, CancellationException,
          ExecutionException, InterruptedException {

        // Attempt to acquire the shared lock with a timeout.
        if (!tryAcquireSharedNanos(-1, nanos)) {
          throw new TimeoutException("Timeout waiting for task.");
        }

        return getValue();
      }

      /**
       * Blocks until {@link #complete(Object, Throwable, int)} has been
       * successfully called.  Throws a {@link CancellationException} if the task
       * was cancelled, or a {@link ExecutionException} if the task completed with
       * an error.
       */
      V get() throws CancellationException, ExecutionException,
          InterruptedException {

        // Acquire the shared lock allowing interruption.
        acquireSharedInterruptibly(-1);
        return getValue();
      }

      /**
       * Implementation of the actual value retrieval.  Will return the value
       * on success, an exception on failure, a cancellation on cancellation, or
       * an illegal state if the synchronizer is in an invalid state.
       */
      private V getValue() throws CancellationException, ExecutionException {
        int state = getState();
        switch (state) {
          case COMPLETED:
            if (exception != null) {
              throw new ExecutionException(exception);
            } else {
              return value;
            }

          case CANCELLED:
          case INTERRUPTED:
            throw cancellationExceptionWithCause(
                "Task was cancelled.", exception);

          default:
            throw new IllegalStateException(
                "Error, synchronizer in invalid state: " + state);
        }
      }

      /**
       * Checks if the state is {@link #COMPLETED}, {@link #CANCELLED}, or {@link #INTERRUPTED}.
       */
      boolean isDone() {
        return (getState() & (COMPLETED | CANCELLED | INTERRUPTED)) != 0;
      }

      /**
       * Checks if the state is {@link #CANCELLED} or {@link #INTERRUPTED}.
       */
      boolean isCancelled() {
        return (getState() & (CANCELLED | INTERRUPTED)) != 0;
      }

      /**
       * Checks if the state is {@link #INTERRUPTED}.
       */
      boolean wasInterrupted() {
        return getState() == INTERRUPTED;
      }

      /**
       * Transition to the COMPLETED state and set the value.
       */
      boolean set(@Nullable V v) {
        return complete(v, null, COMPLETED);
      }

      /**
       * Transition to the COMPLETED state and set the exception.
       */
      boolean setException(Throwable t) {
        return complete(null, t, COMPLETED);
      }

      /**
       * Transition to the CANCELLED or INTERRUPTED state.
       */
      boolean cancel(boolean interrupt) {
        return complete(null, null, interrupt ? INTERRUPTED : CANCELLED);
      }

      /**
       * Implementation of completing a task.  Either {@code v} or {@code t} will
       * be set but not both.  The {@code finalState} is the state to change to
       * from {@link #RUNNING}.  If the state is not in the RUNNING state we
       * return {@code false} after waiting for the state to be set to a valid
       * final state ({@link #COMPLETED}, {@link #CANCELLED}, or {@link
       * #INTERRUPTED}).
       *
       * @param v the value to set as the result of the computation.
       * @param t the exception to set as the result of the computation.
       * @param finalState the state to transition to.
       */
      private boolean complete(@Nullable V v, @Nullable Throwable t,
          int finalState) {
        boolean doCompletion = compareAndSetState(RUNNING, COMPLETING);
        if (doCompletion) {
          // If this thread successfully transitioned to COMPLETING, set the value
          // and exception and then release to the final state.
          this.value = v;
          // Don't actually construct a CancellationException until necessary.
          this.exception = ((finalState & (CANCELLED | INTERRUPTED)) != 0)
              ? new CancellationException("Future.cancel() was called.") : t;
          releaseShared(finalState);
        } else if (getState() == COMPLETING) {
          // If some other thread is currently completing the future, block until
          // they are done so we can guarantee completion.
          acquireShared(-1);
        }
        return doCompletion;
      }
    }

    static final CancellationException cancellationExceptionWithCause(
        @Nullable String message, @Nullable Throwable cause) {
      CancellationException exception = new CancellationException(message);
      exception.initCause(cause);
      return exception;
    }
  }
}

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