Future方式中断线程实现

水深无声 2022-07-28 09:32 204阅读 0赞

# 测试代码 #

**代码如下**

import java.util.concurrent.Callable;
    import java.util.concurrent.ExecutionException;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    import java.util.concurrent.TimeUnit;
    import java.util.concurrent.TimeoutException;
    
    public class ThradPoolTest { 
        private static ExecutorService executor = Executors.newCachedThreadPool();
        protected static int SLEEP_TIME = 2000;
    
    
        /** * @param args */
        public static void main(String[] args) {
            Boolean result =null;
            Future<Boolean> timeOutfuture = executor.submit(new TestJob(SLEEP_TIME*2));
    
            System.out.println("==========timeOutfuture test==============");
            try {
                result = timeOutfuture.get(SLEEP_TIME, TimeUnit.MILLISECONDS);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            } catch (TimeoutException e) {
                System.out.println("Time is out");
                timeOutfuture.cancel(true);
            }
            System.out.println(result); 
    
            Future<Boolean> normalFuture = executor.submit(new TestJob(SLEEP_TIME/2));
            System.out.println("==========normalFuture future test==============");
            try {
                result = normalFuture.get(SLEEP_TIME, TimeUnit.MILLISECONDS);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            } catch (TimeoutException e) {
                System.out.println("Time is out");
                normalFuture.cancel(true);
            }
            System.out.println(result); 
    
            executor.shutdown(); 
        }
    
    
        // 实现Callable接口
        static class TestJob implements Callable<Boolean> {
            private int workTime;
            public TestJob(int workTime){
                this.workTime = workTime;
            }
    
            @Override
            public Boolean call() {
                long startTime = System.currentTimeMillis();
                while(true){
                    for (; System.currentTimeMillis() - startTime < workTime; ) {
                        doSomeThing();
    
                        //判断是否中断
                        if (Thread.interrupted()){
                            return false; 
                        }
                    }
    
                    //任务完成返回
                    return true;
                }
            }
    
            //进行必要的处理
            public void doSomeThing(){}
        }

**说明**：实际上在doSomeThing的方法的实现也很重要，如果这个地方完全阻塞，那么实际上到不了Thread.interrupted()检测的这个方法，线程无法中断。

# JDK FutureTask的canel分析 #

public boolean cancel(boolean mayInterruptIfRunning) {
            if (state != NEW)
                return false;
            if (mayInterruptIfRunning) {
                if (!UNSAFE.compareAndSwapInt(this, stateOffset, NEW, INTERRUPTING))//NEW设置为INTERRUPTING状态
                    return false;
                Thread t = runner;
                if (t != null)
                    t.interrupt();
                UNSAFE.putOrderedInt(this, stateOffset, INTERRUPTED); // final state，设置为INTERRUPTED
            }
            else if (!UNSAFE.compareAndSwapInt(this, stateOffset, NEW, CANCELLED))//如果已经INTERRUPTED，返回false
                return false;
            finishCompletion();//完成收尾工作
            return true;
        }

**说明**  
1. finishCompletion通知相关waiters进行unpark  
2. waiters为future的一个成员变量，Future中的get方法，将当前的线程增加到waiters中，并park自己  
3. waiters为FutureTask中的一个成员变量，为等待队列的队列头

# 参考文档 #

[http://stackoverflow.com/questions/17233038/how-to-implement-synchronous-method-timeouts-in-java][http_stackoverflow.com_questions_17233038_how-to-implement-synchronous-method-timeouts-in-java]  
[http://stackoverflow.com/questions/2275443/how-to-timeout-a-thread][http_stackoverflow.com_questions_2275443_how-to-timeout-a-thread]

[http_stackoverflow.com_questions_17233038_how-to-implement-synchronous-method-timeouts-in-java]: http://stackoverflow.com/questions/17233038/how-to-implement-synchronous-method-timeouts-in-java
[http_stackoverflow.com_questions_2275443_how-to-timeout-a-thread]: http://stackoverflow.com/questions/2275443/how-to-timeout-a-thread