jjeong

구글링 하기 귀찮아서 소소 코드에 있는 주석이랑 코드 가져 왔습니다.

/**
 * 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.
 *
 * @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 all
 * {@link 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 {@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
 * {@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 {@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 {@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.
 * @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
 * {@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 {@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 a 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.
 * @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 {@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.
 * @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 {@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 {@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 {@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);
}

• newFixedThreadPool
• 정해준 크기 만큼의 쓰레드를 생성하고 재사용 합니다. 명시적으로 shutdown() 하지 않는 한 쓰레드 중 하나가 종료 되면 다시 생성을 하게 됩니다.
  

• newWorkStealingPool
• 작업 순서에 대한 보장은 하지 않습니다, parallelism 수준에 따라 쓰레드를 충분히 지원 하지만 다중큐를 사용하는 것이 좋습니다. 쓰레드의 크기는 동적으로 늘었다 줄었다 합니다.
  

• newSingleThreadExecutor
• 쓰레드를 하나만 생성해서 사용합니다. 만약 종료 되면 다시 쓰레드가 생성이 되며 작업에 대한 연속성을 보장해 줍니다.

• newCachedThreadPool
• 필요한 만큼 쓰레드를 생성 하게 됩니다. 하지만 60초 동안 사용되지 않으면 풀에서 제거 됩니다.
• 60초가 기본 설정 값 이며, 생성된 쓰레드는 재사용 됩니다.

• newSingleThreadScheduledExecutor
• 스케쥴링이 가능한 하나의 쓰레드를 생성 합니다. 스케쥴 기능을 빼고는 newSingleThreadExecutor 와 비슷 하다고 보시면 됩니다.
  

• newScheduledThreadPool
• 스케쥴링이 가능한 쓰레드 풀을 생성 합니다. 쓰레드가 idle 상태에 있더라도 종료 되거나 소멸 되지 않고 풀에 그대로 남아 있습니다.