Java线程池（ExecutorService）使用

布满荆棘的人生 2022-05-23 11:45 439阅读 1赞

## 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();
        }
    }

输出：

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();
        }
    }

输出：

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();
        }
    }

输出：

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

*  自己项目中应用：  
    
 *      声名：private ExecutorService asynNotifywxMsgSingleThread = Executors.newSingleThreadExecutor();
 *      使用：	logger.info(JSON.toJSONString(vo));
        	//3.1 pool就单个线程 串行执行， 微信异步推送各消息提醒
        	asynNotifywxMsgSingleThread.execute(new Runnable() {
        	   @Override
        	   public void run() { 
        		try {
        			serviceHandlerMsg.handleOrderStatusToPushStatusMessage(carport);
        		} catch (IOException e) {
        		logger.error("计算order各状态微信推送各消息提醒 fail |"+carportId);
        		e.printStackTrace();
        	    }
        	}
        	});

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   
    
    
    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)
    5.  特别声明：转载地址：https://blog.csdn.net/wanghao\_0206/article/details/76460877