一、前提

  1. /**
  2.  * 线程运行demo，运行时打出线程id以及传入线程中参数
  3.  */
  4. public class ThreadRunner implements Runnable {
  5.  
  6.     private final SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss.SSS");
  7.  
  8.     /**
  9.      * 线程私有属性，创建线程时创建
  10.      */
  11.     private Integer num;
  12.  
  13.     public ThreadRunner(Integer num) {
  14.         this.num = num;
  15.     }
  16.  
  17.     @Override
  18.     public void run() {
  19.         System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + format.format(new Date()) + ",num:" + num);
  20.         try {//使线程睡眠，模拟线程阻塞情况
  21.             TimeUnit.SECONDS.sleep(1);
  22.         } catch (InterruptedException e) {
  23.             e.printStackTrace();
  24.         }
  25.     }
  26. }

二、分类

1、FixedThreadPool-有一个固定大小的线程池

  1. public class FixedThreadPoolDemo {
  2.  
  3.     public static void main(String[] args) {
  4.         ExecutorService pool = Executors.newFixedThreadPool(4);
  5.         for(int i = 0 ; i < 50 ; i++){
  6.             pool.submit(new ThreadRunner((i + 1)));
  7.         }
  8.         pool.shutdown();
  9.     }
  10. }
  11. thread:pool-1-thread-2,time:16:14:45.677,num:2
  12. thread:pool-1-thread-4,time:16:14:45.678,num:4
  13. thread:pool-1-thread-3,time:16:14:45.680,num:3
  14. thread:pool-1-thread-1,time:16:14:45.684,num:1
  15. thread:pool-1-thread-4,time:16:14:46.680,num:5
  16. thread:pool-1-thread-2,time:16:14:46.680,num:6
  17. thread:pool-1-thread-3,time:16:14:46.680,num:7
  18. thread:pool-1-thread-1,time:16:14:46.684,num:8
  19. thread:pool-1-thread-4,time:16:14:47.680,num:9
  20. thread:pool-1-thread-2,time:16:14:47.680,num:10
  21. thread:pool-1-thread-3,time:16:14:47.681,num:11
  22. thread:pool-1-thread-1,time:16:14:47.684,num:12
  23. thread:pool-1-thread-4,time:16:14:48.681,num:13
  24. thread:pool-1-thread-2,time:16:14:48.681,num:14
  25. thread:pool-1-thread-3,time:16:14:48.681,num:15
  26. thread:pool-1-thread-1,time:16:14:48.684,num:16
  27. thread:pool-1-thread-4,time:16:14:49.681,num:17
  28. thread:pool-1-thread-2,time:16:14:49.682,num:18
  29. thread:pool-1-thread-3,time:16:14:49.682,num:19
  30. thread:pool-1-thread-1,time:16:14:49.684,num:20
  31. thread:pool-1-thread-4,time:16:14:50.681,num:21
  32. thread:pool-1-thread-2,time:16:14:50.682,num:22
  33. thread:pool-1-thread-3,time:16:14:50.682,num:23
  34. thread:pool-1-thread-1,time:16:14:50.684,num:24
  35. thread:pool-1-thread-4,time:16:14:51.681,num:25
  36. thread:pool-1-thread-2,time:16:14:51.682,num:26
  37. thread:pool-1-thread-3,time:16:14:51.682,num:27
  38. thread:pool-1-thread-1,time:16:14:51.684,num:28
  39. thread:pool-1-thread-4,time:16:14:52.681,num:29
  40. thread:pool-1-thread-2,time:16:14:52.682,num:30
  41. thread:pool-1-thread-3,time:16:14:52.682,num:31
  42. thread:pool-1-thread-1,time:16:14:52.684,num:32
  43. thread:pool-1-thread-4,time:16:14:53.681,num:33
  44. thread:pool-1-thread-2,time:16:14:53.682,num:34
  45. thread:pool-1-thread-3,time:16:14:53.683,num:35
  46. thread:pool-1-thread-1,time:16:14:53.685,num:36
  47. thread:pool-1-thread-2,time:16:14:54.682,num:38
  48. thread:pool-1-thread-4,time:16:14:54.682,num:37
  49. thread:pool-1-thread-3,time:16:14:54.683,num:39
  50. thread:pool-1-thread-1,time:16:14:54.686,num:40
  51. thread:pool-1-thread-2,time:16:14:55.682,num:41
  52. thread:pool-1-thread-4,time:16:14:55.682,num:42
  53. thread:pool-1-thread-3,time:16:14:55.683,num:43
  54. thread:pool-1-thread-1,time:16:14:55.686,num:44
  55. thread:pool-1-thread-2,time:16:14:56.682,num:45
  56. thread:pool-1-thread-4,time:16:14:56.683,num:46
  57. thread:pool-1-thread-3,time:16:14:56.684,num:47
  58. thread:pool-1-thread-1,time:16:14:56.686,num:48
  59. thread:pool-1-thread-2,time:16:14:57.683,num:49
  60. thread:pool-1-thread-4,time:16:14:57.683,num:50

总结： 
- 池中线程数量固定，不会发生变化 
- 使用无界的LinkedBlockingQueue，要综合考虑生成与消费能力，生成过剩，可能导致堆内存溢出。 
- 适用一些很稳定很固定的正规并发线程，多用于服务器

2、CachedThreadPool

  1. public class CachedThreadPoolDemo {
  2.  
  3.     public static void main(String[] args) {
  4.         ExecutorService pool = Executors.newCachedThreadPool();
  5.         for(int i = 0 ; i < 50 ; i++){
  6.             pool.submit(new ThreadRunner((i + 1)));
  7.         }
  8.         pool.shutdown();
  9.     }
  10. }
  1. thread:pool-1-thread-2,time:16:17:21.289,num:2
  2. thread:pool-1-thread-3,time:16:17:21.290,num:3
  3. thread:pool-1-thread-4,time:16:17:21.290,num:4
  4. thread:pool-1-thread-6,time:16:17:21.291,num:6
  5. thread:pool-1-thread-7,time:16:17:21.291,num:7
  6. thread:pool-1-thread-8,time:16:17:21.291,num:8
  7. thread:pool-1-thread-1,time:16:17:21.292,num:1
  8. thread:pool-1-thread-10,time:16:17:21.293,num:10
  9. thread:pool-1-thread-5,time:16:17:21.294,num:5
  10. thread:pool-1-thread-11,time:16:17:21.294,num:11
  11. thread:pool-1-thread-15,time:16:17:21.294,num:15
  12. thread:pool-1-thread-9,time:16:17:21.294,num:9
  13. thread:pool-1-thread-16,time:16:17:21.295,num:16
  14. thread:pool-1-thread-20,time:16:17:21.295,num:20
  15. thread:pool-1-thread-14,time:16:17:21.296,num:14
  16. thread:pool-1-thread-12,time:16:17:21.296,num:12
  17. thread:pool-1-thread-19,time:16:17:21.297,num:19
  18. thread:pool-1-thread-13,time:16:17:21.299,num:13
  19. thread:pool-1-thread-17,time:16:17:21.300,num:17
  20. thread:pool-1-thread-18,time:16:17:21.302,num:18
  21. thread:pool-1-thread-22,time:16:17:21.304,num:22
  22. thread:pool-1-thread-23,time:16:17:21.304,num:23
  23. thread:pool-1-thread-24,time:16:17:21.305,num:24
  24. thread:pool-1-thread-21,time:16:17:21.305,num:21
  25. thread:pool-1-thread-26,time:16:17:21.305,num:26
  26. thread:pool-1-thread-25,time:16:17:21.306,num:25
  27. thread:pool-1-thread-29,time:16:17:21.307,num:29
  28. thread:pool-1-thread-28,time:16:17:21.308,num:28
  29. thread:pool-1-thread-30,time:16:17:21.308,num:30
  30. thread:pool-1-thread-34,time:16:17:21.308,num:34
  31. thread:pool-1-thread-35,time:16:17:21.308,num:35
  32. thread:pool-1-thread-33,time:16:17:21.308,num:33
  33. thread:pool-1-thread-27,time:16:17:21.309,num:27
  34. thread:pool-1-thread-32,time:16:17:21.308,num:32
  35. thread:pool-1-thread-31,time:16:17:21.309,num:31
  36. thread:pool-1-thread-36,time:16:17:21.310,num:36
  37. thread:pool-1-thread-37,time:16:17:21.310,num:37
  38. thread:pool-1-thread-38,time:16:17:21.310,num:38
  39. thread:pool-1-thread-42,time:16:17:21.310,num:42
  40. thread:pool-1-thread-40,time:16:17:21.310,num:40
  41. thread:pool-1-thread-41,time:16:17:21.311,num:41
  42. thread:pool-1-thread-47,time:16:17:21.762,num:47
  43. thread:pool-1-thread-43,time:16:17:21.762,num:43
  44. thread:pool-1-thread-39,time:16:17:21.762,num:39
  45. thread:pool-1-thread-45,time:16:17:21.762,num:45
  46. thread:pool-1-thread-44,time:16:17:21.763,num:44
  47. thread:pool-1-thread-46,time:16:17:21.761,num:46
  48. thread:pool-1-thread-48,time:16:17:21.761,num:48
  49. thread:pool-1-thread-49,time:16:17:21.765,num:49
  50. thread:pool-1-thread-50,time:16:17:21.765,num:50

总结 
- 池中线程时随着处理数据增加而增加 
- 线程数并不是一直增加，如果有新任务需要执行时，首先查询池中是否有空闲线程并且还为到空闲截止时间，如果有，则使用空闲线程，如果没有，则创建新线程并放入池中。 
- 用于执行一些生存期很短的异步型任务。不适用于IO等长延时操作，因为这可能会创建大量线程，导致系统崩溃。 
- 使用SynchronousQueue作为阻塞队列，如果有新任务进入队列，必须队列中数据被其他线程处理，否则会等待。

3、SingleThreadExecutor

  1. public class SingleThreadPoolDemo {
  2.  
  3.     public static void main(String[] args) {
  4.         ExecutorService pool = Executors.newSingleThreadExecutor();
  5.         for(int i = 0 ; i < 50 ; i++){
  6.             pool.submit(new ThreadRunner((i + 1)));
  7.         }
  8.         pool.shutdown();
  9.     }
  10. }
  1. thread:pool-1-thread-1,time:16:20:10.194,num:1
  2. thread:pool-1-thread-1,time:16:20:11.197,num:2
  3. thread:pool-1-thread-1,time:16:20:12.197,num:3
  4. thread:pool-1-thread-1,time:16:20:13.197,num:4
  5. thread:pool-1-thread-1,time:16:20:14.197,num:5
  6. thread:pool-1-thread-1,time:16:20:15.198,num:6
  7. thread:pool-1-thread-1,time:16:20:16.198,num:7
  8. thread:pool-1-thread-1,time:16:20:17.198,num:8
  9. thread:pool-1-thread-1,time:16:20:18.198,num:9
  10. thread:pool-1-thread-1,time:16:20:19.198,num:10
  11. thread:pool-1-thread-1,time:16:20:20.198,num:11
  12. thread:pool-1-thread-1,time:16:20:21.199,num:12
  13. thread:pool-1-thread-1,time:16:20:22.200,num:13
  14. thread:pool-1-thread-1,time:16:20:23.200,num:14
  15. thread:pool-1-thread-1,time:16:20:24.200,num:15
  16. thread:pool-1-thread-1,time:16:20:25.200,num:16
  17. thread:pool-1-thread-1,time:16:20:26.201,num:17
  18. thread:pool-1-thread-1,time:16:20:27.201,num:18
  19. thread:pool-1-thread-1,time:16:20:28.201,num:19
  20. thread:pool-1-thread-1,time:16:20:29.201,num:20
  21. thread:pool-1-thread-1,time:16:20:30.202,num:21
  22. thread:pool-1-thread-1,time:16:20:31.202,num:22
  23. thread:pool-1-thread-1,time:16:20:32.203,num:23
  24. thread:pool-1-thread-1,time:16:20:33.203,num:24
  25. thread:pool-1-thread-1,time:16:20:34.203,num:25
  26. thread:pool-1-thread-1,time:16:20:35.203,num:26
  27. thread:pool-1-thread-1,time:16:20:36.203,num:27
  28. thread:pool-1-thread-1,time:16:20:37.203,num:28
  29. thread:pool-1-thread-1,time:16:20:38.203,num:29
  30. thread:pool-1-thread-1,time:16:20:39.203,num:30
  31. thread:pool-1-thread-1,time:16:20:40.203,num:31
  32. thread:pool-1-thread-1,time:16:20:41.203,num:32
  33. thread:pool-1-thread-1,time:16:20:42.203,num:33
  34. thread:pool-1-thread-1,time:16:20:43.204,num:34
  35. thread:pool-1-thread-1,time:16:20:44.204,num:35
  36. thread:pool-1-thread-1,time:16:20:45.204,num:36
  37. thread:pool-1-thread-1,time:16:20:46.204,num:37
  38. thread:pool-1-thread-1,time:16:20:47.205,num:38
  39. thread:pool-1-thread-1,time:16:20:48.205,num:39
  40. thread:pool-1-thread-1,time:16:20:49.205,num:40
  41. thread:pool-1-thread-1,time:16:20:50.206,num:41
  42. thread:pool-1-thread-1,time:16:20:51.206,num:42
  43. thread:pool-1-thread-1,time:16:20:52.207,num:43
  44. thread:pool-1-thread-1,time:16:20:53.207,num:44
  45. thread:pool-1-thread-1,time:16:20:54.207,num:45
  46. thread:pool-1-thread-1,time:16:20:55.207,num:46
  47. thread:pool-1-thread-1,time:16:20:56.207,num:47
  48. thread:pool-1-thread-1,time:16:20:57.208,num:48
  49. thread:pool-1-thread-1,time:16:20:58.208,num:49
  50. thread:pool-1-thread-1,time:16:20:59.209,num:50

总结： 
- 线程中只有一个线程在执行 
- 适用于有明确执行顺序但是不影响主线程的任务，压入池中的任务会按照队列顺序执行。 
- 使用无界的LinkedBlockingQueue，要综合考虑生成与消费能力，生成过剩，可能导致堆内存溢出。

三、源码

  1. public static ExecutorService newFixedThreadPool(int nThreads) {
  2.         return new ThreadPoolExecutor(nThreads, nThreads,
  3.                                       0L, TimeUnit.MILLISECONDS,
  4.                                       new LinkedBlockingQueue<Runnable>());
  5. public static ExecutorService newCachedThreadPool() {
  6.         return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
  7.                                       60L, TimeUnit.SECONDS,
  8.                                       new SynchronousQueue<Runnable>());
  9.  public static ExecutorService newSingleThreadExecutor() {
  10.         return new FinalizableDelegatedExecutorService
  11.             (new ThreadPoolExecutor(1, 1,
  12.                                     0L, TimeUnit.MILLISECONDS,
  13.                                     new LinkedBlockingQueue<Runnable>()));
  14.     }

 ThreadPoolExecutor 构造方法*

  1. public ThreadPoolExecutor(int corePoolSize,
  2.                           int maximumPoolSize,
  3.                           long keepAliveTime,
  4.                           TimeUnit unit,
  5.                           BlockingQueue<Runnable> workQueue) {
  6.     this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
  7.          Executors.defaultThreadFactory(), defaultHandler);
  8. }
  9.  
  10.  public ThreadPoolExecutor(int corePoolSize,
  11.                           int maximumPoolSize,
  12.                           long keepAliveTime,
  13.                           TimeUnit unit,
  14.                           BlockingQueue<Runnable> workQueue,
  15.                           ThreadFactory threadFactory,
  16.                           RejectedExecutionHandler handler) {
  17.     if (corePoolSize < 0 ||
  18.         maximumPoolSize <= 0 ||
  19.         maximumPoolSize < corePoolSize ||
  20.         keepAliveTime < 0)
  21.         throw new IllegalArgumentException();
  22.     if (workQueue == null || threadFactory == null || handler == null)
  23.         throw new NullPointerException();
  24.     this.corePoolSize = corePoolSize;
  25.     this.maximumPoolSize = maximumPoolSize;
  26.     this.workQueue = workQueue;
  27.     this.keepAliveTime = unit.toNanos(keepAliveTime);
  28.     this.threadFactory = threadFactory;
  29.     this.handler = handler;
  30. }
    • corePoolSize:线程池核心线程数量 
      1. 如果池中线程数量少于核心线程池数量，则直接新建线程处理当前任务。
      2. 核心线程池空闲不会被回收。
      3. 当池中无空闲线程时，新任务将被添加到阻塞队列
    • maximumPoolSize：线程池最大线程数量 
      1. 当阻塞队列已满，并且有新任务还在入队时，创建新的线程处理，直到线程数大于maximumPoolSize。
      2. 超出corePoolSize部分的线程超过空闲时间后会被回收
      3. 当线程已经超出corePoolSize，并且队列容量已满，则拒绝入队。
    • keepAliveTime unit：线程存活时间 
      1. 当线程超出corePoolSize时生效
      2. 线程空余keepAliveTime后，将被回收
    • workQueue：线程使用阻塞队列
    • threadFactory：创建线程池工厂 
      1. 用于控制创建线程或者销毁线程时加入其它逻辑
    • handler：线程池拒绝策略 
      1. 直接丢弃（DiscardPolicy）
      2. 丢弃队列中最老的任务(DiscardOldestPolicy)。
      3. 抛异常(AbortPolicy)
      4. 将任务分给调用线程来执行(CallerRunsPolicy)

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