https://openjdk.java.net/ 
/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import static java.lang.ref.Reference.reachabilityFence;
import java.security.AccessControlContext;
import java.security.AccessControlException;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.Collection;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import sun.security.util.SecurityConstants;


Factory and utility methods for Executor, ExecutorService, ScheduledExecutorService, ThreadFactory, and Callable classes defined in this package. This class supports the following kinds of methods: 
    
  
  • Methods that create and return an ExecutorService set up with commonly useful configuration settings. 
  • Methods that create and return a ScheduledExecutorService set up with commonly useful configuration settings. 
  • Methods that create and return a "wrapped" ExecutorService, that
      disables reconfiguration by making implementation-specific methods
      inaccessible.
  
  • Methods that create and return a ThreadFactory that sets newly created threads to a known state. 
  • Methods that create and return a Callable out of other closure-like forms, so they can be used in execution methods requiring Callable. 


Author:Doug Lea
Since:1.5
/**
 * Factory and utility methods for {@link Executor}, {@link
 * ExecutorService}, {@link ScheduledExecutorService}, {@link
 * ThreadFactory}, and {@link Callable} classes defined in this
 * package. This class supports the following kinds of methods:
 *
 * <ul>
 *   <li>Methods that create and return an {@link ExecutorService}
 *       set up with commonly useful configuration settings.
 *   <li>Methods that create and return a {@link ScheduledExecutorService}
 *       set up with commonly useful configuration settings.
 *   <li>Methods that create and return a "wrapped" ExecutorService, that
 *       disables reconfiguration by making implementation-specific methods
 *       inaccessible.
 *   <li>Methods that create and return a {@link ThreadFactory}
 *       that sets newly created threads to a known state.
 *   <li>Methods that create and return a {@link Callable}
 *       out of other closure-like forms, so they can be used
 *       in execution methods requiring {@code Callable}.
 * </ul>
 *
 * @since 1.5
 * @author Doug Lea
 */
public class Executors {

    
Creates a thread pool that reuses a fixed number of threads operating off a shared unbounded queue. At any point, at most nThreads 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 shutdown. 
Params:
  • nThreads – the number of threads in the pool
Throws:
Returns:the newly created thread pool
/**
     * Creates a thread pool that reuses a fixed number of threads
     * operating off a shared unbounded queue.  At any point, at most
     * {@code nThreads} 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 {@code nThreads <= 0}
     */
    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

    
Creates a thread pool that maintains enough threads to support
the given parallelism level, and may use multiple queues to
reduce contention. The parallelism level corresponds to the
maximum number of threads actively engaged in, or available to
engage in, task processing. The actual number of threads may
grow and shrink dynamically. A work-stealing pool makes no
guarantees about the order in which submitted tasks are
executed.

Params:
  • parallelism – the targeted parallelism level
Throws:
Returns:the newly created thread pool
Since:1.8
/**
     * Creates a thread pool that maintains enough threads to support
     * the given parallelism level, and may use multiple queues to
     * reduce contention. The parallelism level corresponds to the
     * maximum number of threads actively engaged in, or available to
     * engage in, task processing. The actual number of threads may
     * grow and shrink dynamically. A work-stealing pool makes no
     * guarantees about the order in which submitted tasks are
     * executed.
     *
     * @param parallelism the targeted parallelism level
     * @return the newly created thread pool
     * @throws IllegalArgumentException if {@code parallelism <= 0}
     * @since 1.8
     */
    public static ExecutorService newWorkStealingPool(int parallelism) {
        return new ForkJoinPool
            (parallelism,
             ForkJoinPool.defaultForkJoinWorkerThreadFactory,
             null, true);
    }

    
Creates a work-stealing thread pool using the number of available processors as its target parallelism level. 
See Also:
Returns:the newly created thread pool
Since:1.8
/**
     * Creates a work-stealing thread pool using the number of
     * {@linkplain Runtime#availableProcessors available processors}
     * as its target parallelism level.
     *
     * @return the newly created thread pool
     * @see #newWorkStealingPool(int)
     * @since 1.8
     */
    public static ExecutorService newWorkStealingPool() {
        return new ForkJoinPool
            (Runtime.getRuntime().availableProcessors(),
             ForkJoinPool.defaultForkJoinWorkerThreadFactory,
             null, true);
    }

    
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 nThreads 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 
shutdown. 
Params:
  • nThreads – the number of threads in the pool
  • threadFactory – the factory to use when creating new threads
Throws:
Returns:the newly created thread pool
/**
     * 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 {@code nThreads} 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 {@code nThreads <= 0}
     */
    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 newFixedThreadPool(1) the returned executor is guaranteed not to be reconfigurable to use additional threads. 
Returns:the newly created single-threaded Executor
/**
     * 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
     * {@code newFixedThreadPool(1)} 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>()));
    }

    
Creates an Executor that uses a single worker thread operating off an unbounded queue, and uses the provided ThreadFactory to create a new thread when needed. Unlike the otherwise equivalent newFixedThreadPool(1, threadFactory) the returned executor is guaranteed not to be reconfigurable to use additional threads. 
Params:
  • threadFactory – the factory to use when creating new threads
Throws:
Returns:the newly created single-threaded Executor
/**
     * Creates an Executor that uses a single worker thread operating
     * off an unbounded queue, and uses the provided ThreadFactory to
     * create a new thread when needed. Unlike the otherwise
     * equivalent {@code newFixedThreadPool(1, threadFactory)} the
     * returned executor is guaranteed not to be reconfigurable to use
     * additional threads.
     *
     * @param threadFactory the factory to use when creating new threads
     * @return the newly created single-threaded Executor
     * @throws NullPointerException if threadFactory is null
     */
    public static ExecutorService newSingleThreadExecutor(ThreadFactory threadFactory) {
        return new FinalizableDelegatedExecutorService
            (new ThreadPoolExecutor(1, 1,
                                    0L, TimeUnit.MILLISECONDS,
                                    new LinkedBlockingQueue<Runnable>(),
                                    threadFactory));
    }

    
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 execute 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 ThreadPoolExecutor constructors. 
Returns:the newly created thread pool
/**
     * 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 {@code execute} 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>());
    }

    
Creates a thread pool that creates new threads as needed, but
will reuse previously constructed threads when they are
available, and uses the provided
ThreadFactory to create new threads when needed.

Params:
  • threadFactory – the factory to use when creating new threads
Throws:
Returns:the newly created thread pool
/**
     * Creates a thread pool that creates new threads as needed, but
     * will reuse previously constructed threads when they are
     * available, and uses the provided
     * ThreadFactory to create new threads when needed.
     *
     * @param threadFactory the factory to use when creating new threads
     * @return the newly created thread pool
     * @throws NullPointerException if threadFactory is null
     */
    public static ExecutorService newCachedThreadPool(ThreadFactory threadFactory) {
        return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                      60L, TimeUnit.SECONDS,
                                      new SynchronousQueue<Runnable>(),
                                      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 newScheduledThreadPool(1) the returned executor is guaranteed not to be reconfigurable to use additional threads. 
Returns:the newly created scheduled executor
/**
     * 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
     * {@code newScheduledThreadPool(1)} 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 newScheduledThreadPool(1, threadFactory) the returned executor is guaranteed not to be reconfigurable to use additional threads. 
Params:
  • threadFactory – the factory to use when creating new threads
Throws:
Returns:the newly created scheduled executor
/**
     * 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 {@code newScheduledThreadPool(1, threadFactory)}
     * the returned executor is guaranteed not to be reconfigurable to
     * use additional threads.
     *
     * @param threadFactory the factory to use when creating new threads
     * @return the newly created scheduled executor
     * @throws NullPointerException if threadFactory is null
     */
    public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
        return new DelegatedScheduledExecutorService
            (new ScheduledThreadPoolExecutor(1, threadFactory));
    }

    
Creates a thread pool that can schedule commands to run after a
given delay, or to execute periodically.

Params:
  • corePoolSize – the number of threads to keep in the pool,
even if they are idle
Throws:
Returns:the newly created scheduled thread pool
/**
     * 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 the newly created scheduled thread pool
     * @throws IllegalArgumentException if {@code corePoolSize < 0}
     */
    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.

Params:
  • corePoolSize – the number of threads to keep in the pool,
even if they are idle
  • threadFactory – the factory to use when the executor
creates a new thread
Throws:
Returns:the newly created scheduled thread pool
/**
     * 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 the newly created scheduled thread pool
     * @throws IllegalArgumentException if {@code corePoolSize < 0}
     * @throws NullPointerException if threadFactory is null
     */
    public static ScheduledExecutorService newScheduledThreadPool(
            int corePoolSize, ThreadFactory threadFactory) {
        return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
    }

    
Returns an object that delegates all defined 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. 
Params:
  • executor – the underlying implementation
Throws:
Returns:an ExecutorService instance
/**
     * 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 {@code ExecutorService} instance
     * @throws NullPointerException if executor null
     */
    public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
        if (executor == null)
            throw new NullPointerException();
        return new DelegatedExecutorService(executor);
    }

    
Returns an object that delegates all defined 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. 
Params:
  • executor – the underlying implementation
Throws:
Returns:a ScheduledExecutorService instance
/**
     * 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 {@code ScheduledExecutorService} instance
     * @throws NullPointerException if executor null
     */
    public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
        if (executor == null)
            throw new NullPointerException();
        return new DelegatedScheduledExecutorService(executor);
    }

    
Returns a default thread factory used to create new threads. This factory creates all new threads used by an Executor in the same ThreadGroup. If there is a SecurityManager, it uses the group of System.getSecurityManager, else the group of the thread invoking this defaultThreadFactory method. Each new thread is created as a non-daemon thread with priority set to the smaller of Thread.NORM_PRIORITY and the maximum priority permitted in the thread group. New threads have names accessible via Thread.getName of pool-N-thread-M, where N is the sequence
number of this factory, and M is the sequence number
of the thread created by this factory.

Returns:a thread factory
/**
     * Returns a default thread factory used to create new threads.
     * This factory creates all new threads used by an Executor in the
     * same {@link ThreadGroup}. If there is a {@link
     * java.lang.SecurityManager}, it uses the group of {@link
     * System#getSecurityManager}, else the group of the thread
     * invoking this {@code defaultThreadFactory} method. Each new
     * thread is created as a non-daemon thread with priority set to
     * the smaller of {@code Thread.NORM_PRIORITY} and the maximum
     * priority permitted in the thread group.  New threads have names
     * accessible via {@link Thread#getName} of
     * <em>pool-N-thread-M</em>, where <em>N</em> is the sequence
     * number of this factory, and <em>M</em> is the sequence number
     * of the thread created by this factory.
     * @return a thread factory
     */
    public static ThreadFactory defaultThreadFactory() {
        return new DefaultThreadFactory();
    }

    
Returns a thread factory used to create new threads that have the same permissions as the current thread. This factory creates threads with the same settings as defaultThreadFactory, additionally setting the AccessControlContext and contextClassLoader of new threads to be the same as the thread invoking this privilegedThreadFactory method. A new privilegedThreadFactory can be created within an AccessController.doPrivileged action setting the current thread's access control context to create threads with the selected permission settings holding within that action. 
Note that while tasks running within such threads will have the same access control and class loader settings as the current thread, they need not have the same ThreadLocal or InheritableThreadLocal values. If necessary, particular values of thread locals can be set or reset before any task runs in ThreadPoolExecutor subclasses using ThreadPoolExecutor.beforeExecute(Thread, Runnable). Also, if it is necessary to initialize worker threads to have the same InheritableThreadLocal settings as some other designated thread, you can create a custom ThreadFactory in which that thread waits for and services requests to create others that will inherit its values. 
Throws:
  • AccessControlException – if the current access control
context does not have permission to both get and set context
class loader
Returns:a thread factory
/**
     * Returns a thread factory used to create new threads that
     * have the same permissions as the current thread.
     * This factory creates threads with the same settings as {@link
     * Executors#defaultThreadFactory}, additionally setting the
     * AccessControlContext and contextClassLoader of new threads to
     * be the same as the thread invoking this
     * {@code privilegedThreadFactory} method.  A new
     * {@code privilegedThreadFactory} can be created within an
     * {@link AccessController#doPrivileged AccessController.doPrivileged}
     * action setting the current thread's access control context to
     * create threads with the selected permission settings holding
     * within that action.
     *
     * <p>Note that while tasks running within such threads will have
     * the same access control and class loader settings as the
     * current thread, they need not have the same {@link
     * java.lang.ThreadLocal} or {@link
     * java.lang.InheritableThreadLocal} values. If necessary,
     * particular values of thread locals can be set or reset before
     * any task runs in {@link ThreadPoolExecutor} subclasses using
     * {@link ThreadPoolExecutor#beforeExecute(Thread, Runnable)}.
     * Also, if it is necessary to initialize worker threads to have
     * the same InheritableThreadLocal settings as some other
     * designated thread, you can create a custom ThreadFactory in
     * which that thread waits for and services requests to create
     * others that will inherit its values.
     *
     * @return a thread factory
     * @throws AccessControlException if the current access control
     * context does not have permission to both get and set context
     * class loader
     */
    public static ThreadFactory privilegedThreadFactory() {
        return new PrivilegedThreadFactory();
    }

    
Returns a Callable object that, when called, runs the given task and returns the given result. This can be useful when applying methods requiring a Callable to an otherwise resultless action. 
Params:
  • task – the task to run
  • result – the result to return
Type parameters:
  • <T> – the type of the result
Throws:
Returns:a callable object
/**
     * 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
     * {@code Callable} to an otherwise resultless action.
     * @param task the task to run
     * @param result the result to return
     * @param <T> the type of the result
     * @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 Callable object that, when called, runs the given task and returns null. 
Params:
  • task – the task to run
Throws:
Returns:a callable object
/**
     * Returns a {@link Callable} object that, when
     * called, runs the given task and returns {@code null}.
     * @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 Callable object that, when called, runs the given privileged action and returns its result. 
Params:
  • action – the privileged action to run
Throws:
Returns:a callable object
/**
     * 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 Callable object that, when called, runs the given privileged exception action and returns its result. 
Params:
  • action – the privileged exception action to run
Throws:
Returns:a callable object
/**
     * 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 Callable object that will, when called, execute the given callable under the current access control context. This method should normally be invoked within an 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 AccessControlException. 
Params:
  • callable – the underlying task
Type parameters:
  • <T> – the type of the callable's result
Throws:
Returns:a callable object
/**
     * Returns a {@link Callable} object that will, when called,
     * execute the given {@code callable} under the current access
     * control context. This method should normally be invoked within
     * an {@link AccessController#doPrivileged 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
     * @param <T> the type of the callable's result
     * @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 Callable object that will, when called, execute the given callable 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 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 AccessControlException. 
Params:
  • callable – the underlying task
Type parameters:
  • <T> – the type of the callable's result
Throws:
Returns:a callable object
/**
     * Returns a {@link Callable} object that will, when called,
     * execute the given {@code callable} 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 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
     * @param <T> the type of the callable's result
     * @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);
    }

    // Non-public classes supporting the public methods

    
A callable that runs given task and returns given result.

/**
     * A callable that runs given task and returns given result.
     */
    private static final class RunnableAdapter<T> implements Callable<T> {
        private final Runnable task;
        private final T result;
        RunnableAdapter(Runnable task, T result) {
            this.task = task;
            this.result = result;
        }
        public T call() {
            task.run();
            return result;
        }
        public String toString() {
            return super.toString() + "[Wrapped task = " + task + "]";
        }
    }

    
A callable that runs under established access control settings.

/**
     * A callable that runs under established access control settings.
     */
    private static final class PrivilegedCallable<T> implements Callable<T> {
        final Callable<T> task;
        final AccessControlContext acc;

        PrivilegedCallable(Callable<T> task) {
            this.task = task;
            this.acc = AccessController.getContext();
        }

        public T call() throws Exception {
            try {
                return AccessController.doPrivileged(
                    new PrivilegedExceptionAction<T>() {
                        public T run() throws Exception {
                            return task.call();
                        }
                    }, acc);
            } catch (PrivilegedActionException e) {
                throw e.getException();
            }
        }

        public String toString() {
            return super.toString() + "[Wrapped task = " + task + "]";
        }
    }

    
A callable that runs under established access control settings and
current ClassLoader.

/**
     * A callable that runs under established access control settings and
     * current ClassLoader.
     */
    private static final class PrivilegedCallableUsingCurrentClassLoader<T>
            implements Callable<T> {
        final Callable<T> task;
        final AccessControlContext acc;
        final ClassLoader ccl;

        PrivilegedCallableUsingCurrentClassLoader(Callable<T> task) {
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                // Calls to getContextClassLoader from this class
                // never trigger a security check, but we check
                // whether our callers have this permission anyways.
                sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);

                // Whether setContextClassLoader turns out to be necessary
                // or not, we fail fast if permission is not available.
                sm.checkPermission(new RuntimePermission("setContextClassLoader"));
            }
            this.task = task;
            this.acc = AccessController.getContext();
            this.ccl = Thread.currentThread().getContextClassLoader();
        }

        public T call() throws Exception {
            try {
                return AccessController.doPrivileged(
                    new PrivilegedExceptionAction<T>() {
                        public T run() throws Exception {
                            Thread t = Thread.currentThread();
                            ClassLoader cl = t.getContextClassLoader();
                            if (ccl == cl) {
                                return task.call();
                            } else {
                                t.setContextClassLoader(ccl);
                                try {
                                    return task.call();
                                } finally {
                                    t.setContextClassLoader(cl);
                                }
                            }
                        }
                    }, acc);
            } catch (PrivilegedActionException e) {
                throw e.getException();
            }
        }

        public String toString() {
            return super.toString() + "[Wrapped task = " + task + "]";
        }
    }

    
The default thread factory.

/**
     * The default thread factory.
     */
    private static class DefaultThreadFactory implements ThreadFactory {
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        private final ThreadGroup group;
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        private 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 context and class loader.

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

        PrivilegedThreadFactory() {
            super();
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                // Calls to getContextClassLoader from this class
                // never trigger a security check, but we check
                // whether our callers have this permission anyways.
                sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);

                // Fail fast
                sm.checkPermission(new RuntimePermission("setContextClassLoader"));
            }
            this.acc = AccessController.getContext();
            this.ccl = Thread.currentThread().getContextClassLoader();
        }

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

    
A wrapper class that exposes only the ExecutorService methods
of an ExecutorService implementation.

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

    private static class FinalizableDelegatedExecutorService
            extends DelegatedExecutorService {
        FinalizableDelegatedExecutorService(ExecutorService executor) {
            super(executor);
        }
        @SuppressWarnings("deprecation")
        protected void finalize() {
            super.shutdown();
        }
    }

    
A wrapper class that exposes only the ScheduledExecutorService
methods of a ScheduledExecutorService implementation.

/**
     * A wrapper class that exposes only the ScheduledExecutorService
     * methods of a ScheduledExecutorService implementation.
     */
    private 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);
        }
    }

    
Cannot instantiate. 
/** Cannot instantiate. */
    private Executors() {}
}