Linux排查Java线程数异常

﹏ヽ暗。殇╰゛Y 2022-12-03 08:37 179阅读 0赞

### `1.问题调查分析` ###

发现在代码中使用了线程池 Executors.newFixedThreadPool(20);

`我们先不讨论此处线程池使用是否正确，仅就此处修改而言，将原有 Executors.newFixedThreadPool() 替换；似乎并无不妥（这么修改，是为了遵循阿里规约）`

int nThreads = Runtime.getRuntime().availableProcessors();
            ThreadPoolExecutor pools = new ThreadPoolExecutor(nThreads, nThreads, 120L, TimeUnit.SECONDS,
                    new LinkedBlockingQueue<>(),
                    new ThreadFactoryBuilder().setNameFormat("receive-from-python-thread-pool-%d").build(),
                    new ThreadPoolExecutor.AbortPolicy());

#### `1.1 dump线程分析` ####

`查找到Java程序对应的进程号`

jps -l

`将对应Java程序的线程栈信息转储到thread_dump.log文件`

jstack ${pid_num} > thread_dump.log
    
    
    "pool-165671-thread-1" #188938 prio=5 os_prio=0 tid=0x00007f1a38040000 nid=0x7f19 waiting on condition [0x00007f19065b9000]
       java.lang.Thread.State: WAITING (parking)
            at sun.misc.Unsafe.park(Native Method)
            - parking to wait for  <0x00000000dbb0a178> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
            at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
            at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
            at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
            at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
            at java.lang.Thread.run(Thread.java:745)
    
       Locked ownable synchronizers:
            - None
    
    "pool-164990-thread-1" #188175 prio=5 os_prio=0 tid=0x00007f1a5402c800 nid=0x7a61 waiting on condition [0x00007f18d0d5e000]
       java.lang.Thread.State: WAITING (parking)
            at sun.misc.Unsafe.park(Native Method)
            - parking to wait for  <0x00000000d8c1ef78> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
            at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
            at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
            at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
            at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1067)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1127)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
            at java.lang.Thread.run(Thread.java:745)
    
       Locked ownable synchronizers:
            - None

`原因：程序每次调用方法时，均会创建一个新的线程池来执行任务。但在执行任务后并未关闭该线程池，造成线程无法被回收，线程一直处于等待状态。因而线程数会随时间线性上升`

### `2.总结` ###

这个问题是由于线程池使用不当造成的。使用线程池是为了避免重复、频繁地创建、销毁线程，进而对多个线程进行复用。以上线程池的使用明显未达到该目的，并因为线程池未关闭而造成线程无法被回收，线程数持续增加。