Java线程池的四种策略

拼搏现实的明天。 2022-01-21 01:45 350阅读 0赞

### 文章目录 ###

*  1.AbortPolicy
 *  2.CallerRunsPolicy
 *  3.DiscardOldestPolicy
 *  4.DiscardPolicy

# 1.AbortPolicy #

默认策略，直接跑出异常阻止系统正常运行  
示例代码：

ExecutorService threadPool = new ThreadPoolExecutor(2, 5, 1,
    				TimeUnit.SECONDS, 
    				new LinkedBlockingDeque<Runnable>(3), 
    				Executors.defaultThreadFactory(), new ThreadPoolExecutor.AbortPolicy());
    		
    		for(int i = 0;i<10;i++) { 
    			threadPool.execute(()->{ 
    				System.out.println(Thread.currentThread().getName() +"\t办理业务");
    			});
    		}

这里循环8次以下是没问题的，已到10次，就报错了

pool-1-thread-3	办理业务
    pool-1-thread-3	办理业务
    pool-1-thread-3	办理业务
    pool-1-thread-3	办理业务
    pool-1-thread-5	办理业务
    pool-1-thread-4	办理业务
    pool-1-thread-1	办理业务
    pool-1-thread-2	办理业务
    Exception in thread "main" java.util.concurrent.RejectedExecutionException: Task mst.VolatileDemo$$Lambda$1/142257191@7229724f rejected from java.util.concurrent.ThreadPoolExecutor@4c873330[Running, pool size = 5, active threads = 4, queued tasks = 0, completed tasks = 4]
    	at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
    	at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
    	at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
    	at mst.VolatileDemo.main(VolatileDemo.java:18)

# 2.CallerRunsPolicy #

“调用者运行”一种调节机制，该策略既不会抛弃任务，也不会抛出异常，而是将任务回馈至发起方比如main线程

示例代码:

ExecutorService threadPool = new ThreadPoolExecutor(2, 5, 1,				TimeUnit.SECONDS,
    		new LinkedBlockingDeque<Runnable>(3), 
    		Executors.defaultThreadFactory(), 
    		new ThreadPoolExecutor.CallerRunsPolicy());		
    		
    for(int i = 0;i<10;i++) { 
    	threadPool.execute(()->{ 	
    		System.out.println(Thread.currentThread().getName() +"\t办理业务");
    	});
    }

结果:

main	办理业务
    main	办理业务
    main	办理业务
    main	办理业务
    main	办理业务
    main	办理业务
    main	办理业务
    main	办理业务
    pool-1-thread-5	办理业务
    pool-1-thread-2	办理业务
    pool-1-thread-1	办理业务
    main	办理业务
    pool-1-thread-5	办理业务
    pool-1-thread-3	办理业务
    pool-1-thread-4	办理业务

# 3.DiscardOldestPolicy #

抛弃队列中等待最久的任务，然后把当前任务加入队列中尝试再次提交当前任务

# 4.DiscardPolicy #

直接丢弃任务，不给予任何处理也不跑出异常，如果允许任务丢失，这是最好的一种方案