Java线程池(ExecutorService)使用
Posted 李慕白
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一、前提
/** * 线程运行demo,运行时打出线程id以及传入线程中参数 */ public class ThreadRunner implements Runnable { private final SimpleDateFormat format = new SimpleDateFormat("HH:mm:ss.SSS"); /** * 线程私有属性,创建线程时创建 */ private Integer num; public ThreadRunner(Integer num) { this.num = num; } @Override public void run() { System.out.println("thread:" + Thread.currentThread().getName() + ",time:" + format.format(new Date()) + ",num:" + num); try {//使线程睡眠,模拟线程阻塞情况 TimeUnit.SECONDS.sleep(1); } catch (InterruptedException e) { e.printStackTrace(); } } }
二、分类
1、FixedThreadPool-有一个固定大小的线程池
public class FixedThreadPoolDemo { public static void main(String[] args) { ExecutorService pool = Executors.newFixedThreadPool(4); for(int i = 0 ; i < 50 ; i++){ pool.submit(new ThreadRunner((i + 1))); } pool.shutdown(); } } thread:pool-1-thread-2,time:16:14:45.677,num:2 thread:pool-1-thread-4,time:16:14:45.678,num:4 thread:pool-1-thread-3,time:16:14:45.680,num:3 thread:pool-1-thread-1,time:16:14:45.684,num:1 thread:pool-1-thread-4,time:16:14:46.680,num:5 thread:pool-1-thread-2,time:16:14:46.680,num:6 thread:pool-1-thread-3,time:16:14:46.680,num:7 thread:pool-1-thread-1,time:16:14:46.684,num:8 thread:pool-1-thread-4,time:16:14:47.680,num:9 thread:pool-1-thread-2,time:16:14:47.680,num:10 thread:pool-1-thread-3,time:16:14:47.681,num:11 thread:pool-1-thread-1,time:16:14:47.684,num:12 thread:pool-1-thread-4,time:16:14:48.681,num:13 thread:pool-1-thread-2,time:16:14:48.681,num:14 thread:pool-1-thread-3,time:16:14:48.681,num:15 thread:pool-1-thread-1,time:16:14:48.684,num:16 thread:pool-1-thread-4,time:16:14:49.681,num:17 thread:pool-1-thread-2,time:16:14:49.682,num:18 thread:pool-1-thread-3,time:16:14:49.682,num:19 thread:pool-1-thread-1,time:16:14:49.684,num:20 thread:pool-1-thread-4,time:16:14:50.681,num:21 thread:pool-1-thread-2,time:16:14:50.682,num:22 thread:pool-1-thread-3,time:16:14:50.682,num:23 thread:pool-1-thread-1,time:16:14:50.684,num:24 thread:pool-1-thread-4,time:16:14:51.681,num:25 thread:pool-1-thread-2,time:16:14:51.682,num:26 thread:pool-1-thread-3,time:16:14:51.682,num:27 thread:pool-1-thread-1,time:16:14:51.684,num:28 thread:pool-1-thread-4,time:16:14:52.681,num:29 thread:pool-1-thread-2,time:16:14:52.682,num:30 thread:pool-1-thread-3,time:16:14:52.682,num:31 thread:pool-1-thread-1,time:16:14:52.684,num:32 thread:pool-1-thread-4,time:16:14:53.681,num:33 thread:pool-1-thread-2,time:16:14:53.682,num:34 thread:pool-1-thread-3,time:16:14:53.683,num:35 thread:pool-1-thread-1,time:16:14:53.685,num:36 thread:pool-1-thread-2,time:16:14:54.682,num:38 thread:pool-1-thread-4,time:16:14:54.682,num:37 thread:pool-1-thread-3,time:16:14:54.683,num:39 thread:pool-1-thread-1,time:16:14:54.686,num:40 thread:pool-1-thread-2,time:16:14:55.682,num:41 thread:pool-1-thread-4,time:16:14:55.682,num:42 thread:pool-1-thread-3,time:16:14:55.683,num:43 thread:pool-1-thread-1,time:16:14:55.686,num:44 thread:pool-1-thread-2,time:16:14:56.682,num:45 thread:pool-1-thread-4,time:16:14:56.683,num:46 thread:pool-1-thread-3,time:16:14:56.684,num:47 thread:pool-1-thread-1,time:16:14:56.686,num:48 thread:pool-1-thread-2,time:16:14:57.683,num:49 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
public class CachedThreadPoolDemo { public static void main(String[] args) { ExecutorService pool = Executors.newCachedThreadPool(); for(int i = 0 ; i < 50 ; i++){ pool.submit(new ThreadRunner((i + 1))); } pool.shutdown(); } }
thread:pool-1-thread-2,time:16:17:21.289,num:2 thread:pool-1-thread-3,time:16:17:21.290,num:3 thread:pool-1-thread-4,time:16:17:21.290,num:4 thread:pool-1-thread-6,time:16:17:21.291,num:6 thread:pool-1-thread-7,time:16:17:21.291,num:7 thread:pool-1-thread-8,time:16:17:21.291,num:8 thread:pool-1-thread-1,time:16:17:21.292,num:1 thread:pool-1-thread-10,time:16:17:21.293,num:10 thread:pool-1-thread-5,time:16:17:21.294,num:5 thread:pool-1-thread-11,time:16:17:21.294,num:11 thread:pool-1-thread-15,time:16:17:21.294,num:15 thread:pool-1-thread-9,time:16:17:21.294,num:9 thread:pool-1-thread-16,time:16:17:21.295,num:16 thread:pool-1-thread-20,time:16:17:21.295,num:20 thread:pool-1-thread-14,time:16:17:21.296,num:14 thread:pool-1-thread-12,time:16:17:21.296,num:12 thread:pool-1-thread-19,time:16:17:21.297,num:19 thread:pool-1-thread-13,time:16:17:21.299,num:13 thread:pool-1-thread-17,time:16:17:21.300,num:17 thread:pool-1-thread-18,time:16:17:21.302,num:18 thread:pool-1-thread-22,time:16:17:21.304,num:22 thread:pool-1-thread-23,time:16:17:21.304,num:23 thread:pool-1-thread-24,time:16:17:21.305,num:24 thread:pool-1-thread-21,time:16:17:21.305,num:21 thread:pool-1-thread-26,time:16:17:21.305,num:26 thread:pool-1-thread-25,time:16:17:21.306,num:25 thread:pool-1-thread-29,time:16:17:21.307,num:29 thread:pool-1-thread-28,time:16:17:21.308,num:28 thread:pool-1-thread-30,time:16:17:21.308,num:30 thread:pool-1-thread-34,time:16:17:21.308,num:34 thread:pool-1-thread-35,time:16:17:21.308,num:35 thread:pool-1-thread-33,time:16:17:21.308,num:33 thread:pool-1-thread-27,time:16:17:21.309,num:27 thread:pool-1-thread-32,time:16:17:21.308,num:32 thread:pool-1-thread-31,time:16:17:21.309,num:31 thread:pool-1-thread-36,time:16:17:21.310,num:36 thread:pool-1-thread-37,time:16:17:21.310,num:37 thread:pool-1-thread-38,time:16:17:21.310,num:38 thread:pool-1-thread-42,time:16:17:21.310,num:42 thread:pool-1-thread-40,time:16:17:21.310,num:40 thread:pool-1-thread-41,time:16:17:21.311,num:41 thread:pool-1-thread-47,time:16:17:21.762,num:47 thread:pool-1-thread-43,time:16:17:21.762,num:43 thread:pool-1-thread-39,time:16:17:21.762,num:39 thread:pool-1-thread-45,time:16:17:21.762,num:45 thread:pool-1-thread-44,time:16:17:21.763,num:44 thread:pool-1-thread-46,time:16:17:21.761,num:46 thread:pool-1-thread-48,time:16:17:21.761,num:48 thread:pool-1-thread-49,time:16:17:21.765,num:49 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
public class SingleThreadPoolDemo { public static void main(String[] args) { ExecutorService pool = Executors.newSingleThreadExecutor(); for(int i = 0 ; i < 50 ; i++){ pool.submit(new ThreadRunner((i + 1))); } pool.shutdown(); } }
thread:pool-1-thread-1,time:16:20:10.194,num:1 thread:pool-1-thread-1,time:16:20:11.197,num:2 thread:pool-1-thread-1,time:16:20:12.197,num:3 thread:pool-1-thread-1,time:16:20:13.197,num:4 thread:pool-1-thread-1,time:16:20:14.197,num:5 thread:pool-1-thread-1,time:16:20:15.198,num:6 thread:pool-1-thread-1,time:16:20:16.198,num:7 thread:pool-1-thread-1,time:16:20:17.198,num:8 thread:pool-1-thread-1,time:16:20:18.198,num:9 thread:pool-1-thread-1,time:16:20:19.198,num:10 thread:pool-1-thread-1,time:16:20:20.198,num:11 thread:pool-1-thread-1,time:16:20:21.199,num:12 thread:pool-1-thread-1,time:16:20:22.200,num:13 thread:pool-1-thread-1,time:16:20:23.200,num:14 thread:pool-1-thread-1,time:16:20:24.200,num:15 thread:pool-1-thread-1,time:16:20:25.200,num:16 thread:pool-1-thread-1,time:16:20:26.201,num:17 thread:pool-1-thread-1,time:16:20:27.201,num:18 thread:pool-1-thread-1,time:16:20:28.201,num:19 thread:pool-1-thread-1,time:16:20:29.201,num:20 thread:pool-1-thread-1,time:16:20:30.202,num:21 thread:pool-1-thread-1,time:16:20:31.202,num:22 thread:pool-1-thread-1,time:16:20:32.203,num:23 thread:pool-1-thread-1,time:16:20:33.203,num:24 thread:pool-1-thread-1,time:16:20:34.203,num:25 thread:pool-1-thread-1,time:16:20:35.203,num:26 thread:pool-1-thread-1,time:16:20:36.203,num:27 thread:pool-1-thread-1,time:16:20:37.203,num:28 thread:pool-1-thread-1,time:16:20:38.203,num:29 thread:pool-1-thread-1,time:16:20:39.203,num:30 thread:pool-1-thread-1,time:16:20:40.203,num:31 thread:pool-1-thread-1,time:16:20:41.203,num:32 thread:pool-1-thread-1,time:16:20:42.203,num:33 thread:pool-1-thread-1,time:16:20:43.204,num:34 thread:pool-1-thread-1,time:16:20:44.204,num:35 thread:pool-1-thread-1,time:16:20:45.204,num:36 thread:pool-1-thread-1,time:16:20:46.204,num:37 thread:pool-1-thread-1,time:16:20:47.205,num:38 thread:pool-1-thread-1,time:16:20:48.205,num:39 thread:pool-1-thread-1,time:16:20:49.205,num:40 thread:pool-1-thread-1,time:16:20:50.206,num:41 thread:pool-1-thread-1,time:16:20:51.206,num:42 thread:pool-1-thread-1,time:16:20:52.207,num:43 thread:pool-1-thread-1,time:16:20:53.207,num:44 thread:pool-1-thread-1,time:16:20:54.207,num:45 thread:pool-1-thread-1,time:16:20:55.207,num:46 thread:pool-1-thread-1,time:16:20:56.207,num:47 thread:pool-1-thread-1,time:16:20:57.208,num:48 thread:pool-1-thread-1,time:16:20:58.208,num:49 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
public static ExecutorService newFixedThreadPool(int nThreads) { return new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>()); public static ExecutorService newCachedThreadPool() { return new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>()); public static ExecutorService newSingleThreadExecutor() { return new FinalizableDelegatedExecutorService (new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>())); }
ThreadPoolExecutor 构造方法*
public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue) { this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, Executors.defaultThreadFactory(), defaultHandler); } public ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue, ThreadFactory threadFactory, RejectedExecutionHandler handler) { if (corePoolSize < 0 || maximumPoolSize <= 0 || maximumPoolSize < corePoolSize || keepAliveTime < 0) throw new IllegalArgumentException(); if (workQueue == null || threadFactory == null || handler == null) throw new NullPointerException(); this.corePoolSize = corePoolSize; this.maximumPoolSize = maximumPoolSize; this.workQueue = workQueue; this.keepAliveTime = unit.toNanos(keepAliveTime); this.threadFactory = threadFactory; this.handler = handler; }
- corePoolSize:线程池核心线程数量
- 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。
- 核心线程池空闲不会被回收。
- 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
- 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。
- 超出corePoolSize部分的线程超过空闲时间后会被回收
- 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
- 当线程超出corePoolSize时生效
- 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
- 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
- 直接丢弃(DiscardPolicy)
- 丢弃队列中最老的任务(DiscardOldestPolicy)。
- 抛异常(AbortPolicy)
- 将任务分给调用线程来执行(CallerRunsPolicy)
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