线程池执行过程中遇到异常会发生什么?怎样处理?
发布网友
发布时间：2024-09-25 16:52
共1个回答
热心网友
时间：2024-10-16 21:15
这个好理解，当线程出现未捕获异常的时候就执行不下去了，留给它的就是垃圾回收了。
线程池中线程频繁出现未捕获异常当线程池中线程频繁出现未捕获的异常，那线程的复用率就大大降低了，需要不断地创建新线程。
做个实验：
publicclassThreadExecutor{privateThreadPoolExecutorthreadPoolExecutor=newThreadPoolExecutor(1,1,60,TimeUnit.SECONDS,newArrayBlockingQueue<>(200),newThreadFactoryBuilder().setNameFormat("customThread%d").build());@Testpublicvoidtest(){IntStream.rangeClosed(1,5).forEach(i->{try{Thread.sleep(100);}catch(InterruptedExceptione){e.printStackTrace();}threadPoolExecutor.execute(()->{intj=1/0;});});}}新建一个只有一个线程的线程池，每隔0.1s提交一个任务，任务中是一个1/0的计算。
Exceptioninthread"customThread0"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread1"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread2"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread3"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread4"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread5"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)可见每次执行的线程都不一样，之前的线程都没有复用。原因是因为出现了未捕获的异常。
我们把异常捕获试试：
publicclassThreadExecutor{privateThreadPoolExecutorthreadPoolExecutor=newThreadPoolExecutor(1,1,60,TimeUnit.SECONDS,newArrayBlockingQueue<>(200),newThreadFactoryBuilder().setNameFormat("customThread%d").build());@Testpublicvoidtest(){IntStream.rangeClosed(1,5).forEach(i->{try{Thread.sleep(100);}catch(InterruptedExceptione){e.printStackTrace();}threadPoolExecutor.execute(()->{try{intj=1/0;}catch(Exceptione){System.out.println(Thread.currentThread().getName()+""+e.getMessage());}});});}}customThread0/byzerocustomThread0/byzerocustomThread0/byzerocustomThread0/byzerocustomThread0/byzero可见当异常捕获了，线程就可以复用了。
问题来了，我们的代码中异常不可能全部捕获如果要捕获那些没被业务代码捕获的异常，可以设置Thread类的uncaughtExceptionHandler属性。这时使用ThreadFactoryBuilder会比较方便，ThreadFactoryBuilder是guava提供的ThreadFactory生成器。
newThreadFactoryBuilder().setNameFormat("customThread%d").setUncaughtExceptionHandler((t,e)->System.out.println(t.getName()+"发生异常"+e.getCause())).build()修改之后：
publicclassThreadExecutor{privatestaticThreadPoolExecutorthreadPoolExecutor=newThreadPoolExecutor(1,1,60,TimeUnit.SECONDS,newArrayBlockingQueue<>(200),newThreadFactoryBuilder().setNameFormat("customThread%d").setUncaughtExceptionHandler((t,e)->System.out.println("UncaughtExceptionHandler捕获到："+t.getName()+"发生异常"+e.getMessage())).build());@Testpublicvoidtest(){IntStream.rangeClosed(1,5).forEach(i->{try{Thread.sleep(100);}catch(InterruptedExceptione){e.printStackTrace();}threadPoolExecutor.execute(()->{System.out.println("线程"+Thread.currentThread().getName()+"执行");intj=1/0;});});}}线程customThread0执行UncaughtExceptionHandler捕获到：customThread0发生异常/byzero线程customThread1执行UncaughtExceptionHandler捕获到：customThread1发生异常/byzero线程customThread2执行UncaughtExceptionHandler捕获到：customThread2发生异常/byzero线程customThread3执行UncaughtExceptionHandler捕获到：customThread3发生异常/byzero线程customThread4执行UncaughtExceptionHandler捕获到：customThread4发生异常/byzero可见，结果并不是我们想象的那样，线程池中原有的线程没有复用！所以通过UncaughtExceptionHandler想将异常吞掉使线程复用这招貌似行不通。它只是做了一层异常的保底处理。
将excute改成submit试试
publicclassThreadExecutor{privatestaticThreadPoolExecutorthreadPoolExecutor=newThreadPoolExecutor(1,1,60,TimeUnit.SECONDS,newArrayBlockingQueue<>(200),newThreadFactoryBuilder().setNameFormat("customThread%d").setUncaughtExceptionHandler((t,e)->System.out.println("UncaughtExceptionHandler捕获到："+t.getName()+"发生异常"+e.getMessage())).build());@Testpublicvoidtest(){IntStream.rangeClosed(1,5).forEach(i->{try{Thread.sleep(100);}catch(InterruptedExceptione){e.printStackTrace();}Future<?>future=threadPoolExecutor.submit(()->{System.out.println("线程"+Thread.currentThread().getName()+"执行");intj=1/0;});try{future.get();}catch(InterruptedExceptione){e.printStackTrace();}catch(ExecutionExceptione){e.printStackTrace();}});}}线程customThread0执行java.util.concurrent.ExecutionException:java.lang.ArithmeticException:/byzero线程customThread0执行java.util.concurrent.ExecutionException:java.lang.ArithmeticException:/byzero线程customThread0执行java.util.concurrent.ExecutionException:java.lang.ArithmeticException:/byzero线程customThread0执行java.util.concurrent.ExecutionException:java.lang.ArithmeticException:/byzero线程customThread0执行java.util.concurrent.ExecutionException:java.lang.ArithmeticException:/byzero通过submit提交线程可以屏蔽线程中产生的异常，达到线程复用。当get()执行结果时异常才会抛出。
原因是通过submit提交的线程，当发生异常时，会将异常保存，待future.get();时才会抛出。
这是Futuretask的部分run()方法，看setException：
publicvoidrun(){try{Callable<V>c=callable;if(c!=null&&state==NEW){Vresult;booleanran;try{result=c.call();ran=true;}catch(Throwableex){result=null;ran=false;setException(ex);}if(ran)set(result);}}}protectedvoidsetException(Throwablet){if(UNSAFE.compareAndSwapInt(this,stateOffset,NEW,COMPLETING)){outcome=t;UNSAFE.putOrderedInt(this,stateOffset,EXCEPTIONAL);//finalstatefinishCompletion();}}将异常存在outcome对象中，没有抛出，再看get方法：
Exceptioninthread"customThread0"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread1"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread2"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread3"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread4"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)Exceptioninthread"customThread5"java.lang.ArithmeticException:/byzeroatthread.ThreadExecutor.lambda$null$0(ThreadExecutor.java:25)atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:748)0当outcome是异常时才抛出。
总结1、线程池中线程中异常尽量手动捕获
2、通过设置ThreadFactory的UncaughtExceptionHandler可以对未捕获的异常做保底处理，通过execute提交任务，线程依然会中断，而通过submit提交任务，可以获取线程执行结果，线程异常会在get执行结果时抛出。
原文链接：https://blog.csdn.net/weixin_37968613/article/details/108407774
