/**
 * Creates a thread pool that reuses a fixed number of threads
 * operating off a shared unbounded queue.  At any point, at most
 * <tt>nThreads</tt> threads will be active processing tasks.
 * If additional tasks are submitted when all threads are active,
 * they will wait in the queue until a thread is available.
 * If any thread terminates due to a failure during execution
 * prior to shutdown, a new one will take its place if needed to
 * execute subsequent tasks.  The threads in the pool will exist
 * until it is explicitly {@link ExecutorService#shutdown shutdown}.
 *
 * @param nThreads the number of threads in the pool
 * @return the newly created thread pool
 * @throws IllegalArgumentException if <tt>nThreads &lt;= 0</tt>
 */
public static ExecutorService newFixedThreadPool(int nThreads) {
    return new ThreadPoolExecutor(nThreads, nThreads,
                                  0L, TimeUnit.MILLISECONDS,
                                  new LinkedBlockingQueue<Runnable>());
}

/**
 * Creates a thread pool that reuses a fixed number of threads
 * operating off a shared unbounded queue, using the provided
 * ThreadFactory to create new threads when needed.  At any point,
 * at most <tt>nThreads</tt> threads will be active processing
 * tasks.  If additional tasks are submitted when all threads are
 * active, they will wait in the queue until a thread is
 * available.  If any thread terminates due to a failure during
 * execution prior to shutdown, a new one will take its place if
 * needed to execute subsequent tasks.  The threads in the pool will
 * exist until it is explicitly {@link ExecutorService#shutdown
 * shutdown}.
 *
 * @param nThreads the number of threads in the pool
 * @param threadFactory the factory to use when creating new threads
 * @return the newly created thread pool
 * @throws NullPointerException if threadFactory is null
 * @throws IllegalArgumentException if <tt>nThreads &lt;= 0</tt>
 */
public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
    return new ThreadPoolExecutor(nThreads, nThreads,
                                  0L, TimeUnit.MILLISECONDS,
                                  new LinkedBlockingQueue<Runnable>(),
                                  threadFactory);
}

/**
 * Creates an Executor that uses a single worker thread operating
 * off an unbounded queue. (Note however that if this single
 * thread terminates due to a failure during execution prior to
 * shutdown, a new one will take its place if needed to execute
 * subsequent tasks.)  Tasks are guaranteed to execute
 * sequentially, and no more than one task will be active at any
 * given time. Unlike the otherwise equivalent
 * <tt>newFixedThreadPool(1)</tt> the returned executor is
 * guaranteed not to be reconfigurable to use additional threads.
 *
 * @return the newly created single-threaded Executor
 */
public static ExecutorService newSingleThreadExecutor() {
    return new FinalizableDelegatedExecutorService
        (new ThreadPoolExecutor(1, 1,
                                0L, TimeUnit.MILLISECONDS,
                                new LinkedBlockingQueue<Runnable>()));
}

  static class FinalizableDelegatedExecutorService
extends DelegatedExecutorService {
FinalizableDelegatedExecutorService(ExecutorService executor) {
    super(executor);
}
protected void finalize()  {
       // 1
    super.shutdown();
}
   }

/**
     * A wrapper class that exposes only the ExecutorService methods
     * of an ExecutorService implementation.
     */
    static class DelegatedExecutorService extends AbstractExecutorService {
        private final ExecutorService e;
        DelegatedExecutorService(ExecutorService executor) { e = executor; }
        public void execute(Runnable command) { e.execute(command); }
        public void shutdown() { e.shutdown(); }
        public List<Runnable> shutdownNow() { return e.shutdownNow(); }
        public boolean isShutdown() { return e.isShutdown(); }
        public boolean isTerminated() { return e.isTerminated(); }
        public boolean awaitTermination(long timeout, TimeUnit unit)
            throws InterruptedException {
            return e.awaitTermination(timeout, unit);
        }
        public Future<?> submit(Runnable task) {
            return e.submit(task);
        }
        public <T> Future<T> submit(Callable<T> task) {
            return e.submit(task);
        }
        public <T> Future<T> submit(Runnable task, T result) {
            return e.submit(task, result);
        }
        public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
            throws InterruptedException {
            return e.invokeAll(tasks);
        }
        public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                             long timeout, TimeUnit unit)
            throws InterruptedException {
            return e.invokeAll(tasks, timeout, unit);
        }
        public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
            throws InterruptedException, ExecutionException {
            return e.invokeAny(tasks);
        }
        public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
                               long timeout, TimeUnit unit)
            throws InterruptedException, ExecutionException, TimeoutException {
            return e.invokeAny(tasks, timeout, unit);
        }
    }

/**
    * Creates a thread pool that creates new threads as needed, but
    * will reuse previously constructed threads when they are
    * available.  These pools will typically improve the performance
    * of programs that execute many short-lived asynchronous tasks.
    * Calls to <tt>execute</tt> will reuse previously constructed
    * threads if available. If no existing thread is available, a new
    * thread will be created and added to the pool. Threads that have
    * not been used for sixty seconds are terminated and removed from
    * the cache. Thus, a pool that remains idle for long enough will
    * not consume any resources. Note that pools with similar
    * properties but different details (for example, timeout parameters)
    * may be created using {@link ThreadPoolExecutor} constructors.
    *
    * @return the newly created thread pool
    */
   public static ExecutorService newCachedThreadPool() {
       return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                     60L, TimeUnit.SECONDS,
                                     new SynchronousQueue<Runnable>());
   }

/**
 * Returns an object that delegates all defined {@link
 * ExecutorService} methods to the given executor, but not any
 * other methods that might otherwise be accessible using
 * casts. This provides a way to safely "freeze" configuration and
 * disallow tuning of a given concrete implementation.
 * @param executor the underlying implementation
 * @return an <tt>ExecutorService</tt> instance
 * @throws NullPointerException if executor null
 */
public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
    if (executor == null)
        throw new NullPointerException();
    return new DelegatedExecutorService(executor);
}

/**
 * Creates a thread pool that can schedule commands to run after a
 * given delay, or to execute periodically.
 * @param corePoolSize the number of threads to keep in the pool,
 * even if they are idle.
 * @return a newly created scheduled thread pool
 * @throws IllegalArgumentException if <tt>corePoolSize &lt; 0</tt>
 */
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
    return new ScheduledThreadPoolExecutor(corePoolSize);
}

/**
 * Creates a thread pool that can schedule commands to run after a
 * given delay, or to execute periodically.
 * @param corePoolSize the number of threads to keep in the pool,
 * even if they are idle.
 * @param threadFactory the factory to use when the executor
 * creates a new thread.
 * @return a newly created scheduled thread pool
 * @throws IllegalArgumentException if <tt>corePoolSize &lt; 0</tt>
 * @throws NullPointerException if threadFactory is null
 */
public static ScheduledExecutorService newScheduledThreadPool(
        int corePoolSize, ThreadFactory threadFactory) {
    return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
}

/**
     * Creates a single-threaded executor that can schedule commands
     * to run after a given delay, or to execute periodically.
     * (Note however that if this single
     * thread terminates due to a failure during execution prior to
     * shutdown, a new one will take its place if needed to execute
     * subsequent tasks.)  Tasks are guaranteed to execute
     * sequentially, and no more than one task will be active at any
     * given time. Unlike the otherwise equivalent
     * <tt>newScheduledThreadPool(1)</tt> the returned executor is
     * guaranteed not to be reconfigurable to use additional threads.
     * @return the newly created scheduled executor
     */
    public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
        return new DelegatedScheduledExecutorService
            (new ScheduledThreadPoolExecutor(1));
    }

    /**
     * Creates a single-threaded executor that can schedule commands
     * to run after a given delay, or to execute periodically.  (Note
     * however that if this single thread terminates due to a failure
     * during execution prior to shutdown, a new one will take its
     * place if needed to execute subsequent tasks.)  Tasks are
     * guaranteed to execute sequentially, and no more than one task
     * will be active at any given time. Unlike the otherwise
     * equivalent <tt>newScheduledThreadPool(1, threadFactory)</tt>
     * the returned executor is guaranteed not to be reconfigurable to
     * use additional threads.
     * @param threadFactory the factory to use when creating new
     * threads
     * @return a newly created scheduled executor
     * @throws NullPointerException if threadFactory is null
     */
    public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
        return new DelegatedScheduledExecutorService
            (new ScheduledThreadPoolExecutor(1, threadFactory));
    }

/**
     * A wrapper class that exposes only the ScheduledExecutorService
     * methods of a ScheduledExecutorService implementation.
     */
    static class DelegatedScheduledExecutorService
            extends DelegatedExecutorService
            implements ScheduledExecutorService {
        private final ScheduledExecutorService e;
        DelegatedScheduledExecutorService(ScheduledExecutorService executor) {
            super(executor);
            e = executor;
        }
        public ScheduledFuture<?> schedule(Runnable command, long delay,  TimeUnit unit) {
            return e.schedule(command, delay, unit);
        }
        public <V> ScheduledFuture<V> schedule(Callable<V> callable, long delay, TimeUnit unit) {
            return e.schedule(callable, delay, unit);
        }
        public ScheduledFuture<?> scheduleAtFixedRate(Runnable command, long initialDelay,  long period, TimeUnit unit) {
            return e.scheduleAtFixedRate(command, initialDelay, period, unit);
        }
        public ScheduledFuture<?> scheduleWithFixedDelay(Runnable command, long initialDelay,  long delay, TimeUnit unit) {
            return e.scheduleWithFixedDelay(command, initialDelay, delay, unit);
        }
    }

/**
    * Returns an object that delegates all defined {@link
    * ScheduledExecutorService} methods to the given executor, but
    * not any other methods that might otherwise be accessible using
    * casts. This provides a way to safely "freeze" configuration and
    * disallow tuning of a given concrete implementation.
    * @param executor the underlying implementation
    * @return a <tt>ScheduledExecutorService</tt> instance
    * @throws NullPointerException if executor null
    */
   public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
       if (executor == null)
           throw new NullPointerException();
       return new DelegatedScheduledExecutorService(executor);
   }

/**
 * The default thread factory
 */
static class DefaultThreadFactory implements ThreadFactory {
    static final AtomicInteger poolNumber = new AtomicInteger(1);
    final ThreadGroup group;
    final AtomicInteger threadNumber = new AtomicInteger(1);
    final String namePrefix;

    DefaultThreadFactory() {
        SecurityManager s = System.getSecurityManager();
        group = (s != null)? s.getThreadGroup() :
                             Thread.currentThread().getThreadGroup();
        namePrefix = "pool-" +
                      poolNumber.getAndIncrement() +
                     "-thread-";
    }

    public Thread newThread(Runnable r) {
        Thread t = new Thread(group, r,
                              namePrefix + threadNumber.getAndIncrement(),
                              0);
        if (t.isDaemon())
            t.setDaemon(false);
        if (t.getPriority() != Thread.NORM_PRIORITY)
            t.setPriority(Thread.NORM_PRIORITY);
        return t;
    }
}

/**
     *  Thread factory capturing access control and class loader
     */
    static class PrivilegedThreadFactory extends DefaultThreadFactory {
        private final ClassLoader ccl;
        private final AccessControlContext acc;

        PrivilegedThreadFactory() {
            super();
            this.ccl = Thread.currentThread().getContextClassLoader();
            this.acc = AccessController.getContext();
            acc.checkPermission(new RuntimePermission("setContextClassLoader"));
        }

        public Thread newThread(final Runnable r) {
            return super.newThread(new Runnable() {
                public void run() {
                    AccessController.doPrivileged(new PrivilegedAction<Object>() {
                        public Object run() {
                            Thread.currentThread().setContextClassLoader(ccl);
                            r.run();
                            return null;
                        }
                    }, acc);
                }
            });
        }

    }

/**
     * Returns a {@link Callable} object that, when
     * called, runs the given task and returns the given result.  This
     * can be useful when applying methods requiring a
     * <tt>Callable</tt> to an otherwise resultless action.
     * @param task the task to run
     * @param result the result to return
     * @return a callable object
     * @throws NullPointerException if task null
     */
    public static <T> Callable<T> callable(Runnable task, T result) {
        if (task == null)
            throw new NullPointerException();
        return new RunnableAdapter<T>(task, result);
    }

    /**
     * Returns a {@link Callable} object that, when
     * called, runs the given task and returns <tt>null</tt>.
     * @param task the task to run
     * @return a callable object
     * @throws NullPointerException if task null
     */
    public static Callable<Object> callable(Runnable task) {
        if (task == null)
            throw new NullPointerException();
        return new RunnableAdapter<Object>(task, null);
    }

    /**
     * Returns a {@link Callable} object that, when
     * called, runs the given privileged action and returns its result.
     * @param action the privileged action to run
     * @return a callable object
     * @throws NullPointerException if action null
     */
    public static Callable<Object> callable(final PrivilegedAction<?> action) {
        if (action == null)
            throw new NullPointerException();
        return new Callable<Object>() {
	    public Object call() { return action.run(); }};
    }

    /**
     * Returns a {@link Callable} object that, when
     * called, runs the given privileged exception action and returns
     * its result.
     * @param action the privileged exception action to run
     * @return a callable object
     * @throws NullPointerException if action null
     */
    public static Callable<Object> callable(final PrivilegedExceptionAction<?> action) {
        if (action == null)
            throw new NullPointerException();
	return new Callable<Object>() {
	    public Object call() throws Exception { return action.run(); }};
    }

    /**
     * Returns a {@link Callable} object that will, when
     * called, execute the given <tt>callable</tt> under the current
     * access control context. This method should normally be
     * invoked within an {@link AccessController#doPrivileged} action
     * to create callables that will, if possible, execute under the
     * selected permission settings holding within that action; or if
     * not possible, throw an associated {@link
     * AccessControlException}.
     * @param callable the underlying task
     * @return a callable object
     * @throws NullPointerException if callable null
     *
     */
    public static <T> Callable<T> privilegedCallable(Callable<T> callable) {
        if (callable == null)
            throw new NullPointerException();
        return new PrivilegedCallable<T>(callable);
    }

    /**
     * Returns a {@link Callable} object that will, when
     * called, execute the given <tt>callable</tt> under the current
     * access control context, with the current context class loader
     * as the context class loader. This method should normally be
     * invoked within an {@link AccessController#doPrivileged} action
     * to create callables that will, if possible, execute under the
     * selected permission settings holding within that action; or if
     * not possible, throw an associated {@link
     * AccessControlException}.
     * @param callable the underlying task
     *
     * @return a callable object
     * @throws NullPointerException if callable null
     * @throws AccessControlException if the current access control
     * context does not have permission to both set and get context
     * class loader.
     */
    public static <T> Callable<T> privilegedCallableUsingCurrentClassLoader(Callable<T> callable) {
        if (callable == null)
            throw new NullPointerException();
        return new PrivilegedCallableUsingCurrentClassLoader<T>(callable);
    }

/**
 * A callable that runs given task and returns given result
 */
static final class RunnableAdapter<T> implements Callable<T> {
    final Runnable task;
    final T result;
    RunnableAdapter(Runnable  task, T result) {
        this.task = task;
        this.result = result;
    }
    public T call() {
        task.run();
        return result;
    }
}

/**
 * A callable that runs under established access control settings
 */
static final class PrivilegedCallable<T> implements Callable<T> {
    private final AccessControlContext acc;
    private final Callable<T> task;
    private T result;
    private Exception exception;
    PrivilegedCallable(Callable<T> task) {
        this.task = task;
        this.acc = AccessController.getContext();
    }

    public T call() throws Exception {
        AccessController.doPrivileged(new PrivilegedAction<T>() {
                public T run() {
                    try {
                        result = task.call();
                    } catch (Exception ex) {
                        exception = ex;
                    }
                    return null;
                }
            }, acc);
        if (exception != null)
            throw exception;
        else
            return result;
    }
}