程序完成后 Java 挂起一分钟

Question

我们有一个在大型应用程序的构建过程中使用的 Java 命令行实用程序。从最近开始(显然是在将 Java 升级到 OpenJDK 运行时环境(build 1.8.0_212-b04)之后——该程序不经常使用，所以我没有注意到这到底是什么时候开始发生的)它在 main() 之后挂起大约一分钟完成的。 IE。它卡在 Java 内部的某个地方，不在我们的代码中，尽管我们的代码可能会以某种方式间接导致这种情况。

该程序使用 Javassist (3.25) 检测一些先前使用 javac 编译的 Java 类。不幸的是，我无法发布该程序本身，因为它非常庞大、复杂并且也是专有的。

挂起大约一分钟后，程序正常退出——进程返回代码为零，没有任何内容打印到 stderr 或 stdout。产生的结果也符合预期。

下面是使用 jstack 实用程序从“挂起”的进程中提取的线程堆栈转储。如您所见，不再有线程从我们的程序中执行任何操作，此时所有线程都在 Java 内部。

有没有人遇到过类似的事情或者知道发生了什么事？

2019-05-22 12:51:34
Full thread dump OpenJDK 64-Bit Server VM (25.212-b04 mixed mode):

"Attach Listener" #12 daemon prio=9 os_prio=0 tid=0x00007f196c001000 nid=0x3c3a waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"DestroyJavaVM" #11 prio=5 os_prio=0 tid=0x00007f19c0059800 nid=0x3b6c waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"pool-1-thread-1" #10 prio=5 os_prio=0 tid=0x00007f19c0d1b800 nid=0x3b8e waiting on condition [0x00007f1985f21000]
   java.lang.Thread.State: TIMED_WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x0000000776280730> (a java.util.concurrent.SynchronousQueue$TransferStack)
        at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
        at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)
        at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:362)
        at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1073)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

"Service Thread" #9 daemon prio=9 os_prio=0 tid=0x00007f19c0145800 nid=0x3b87 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread3" #8 daemon prio=9 os_prio=0 tid=0x00007f19c013a000 nid=0x3b86 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread2" #7 daemon prio=9 os_prio=0 tid=0x00007f19c0138000 nid=0x3b85 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007f19c0136000 nid=0x3b84 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007f19c0133000 nid=0x3b83 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007f19c0126800 nid=0x3b82 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007f19c00fa800 nid=0x3b81 in Object.wait() [0x00007f198727c000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000776289088> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
        - locked <0x0000000776289088> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
        at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

"Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007f19c00f5800 nid=0x3b80 in Object.wait() [0x00007f198737d000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000776280990> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Object.java:502)
        at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
        - locked <0x0000000776280990> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

"VM Thread" os_prio=0 tid=0x00007f19c00ec000 nid=0x3b7f runnable 

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007f19c006c000 nid=0x3b6d runnable 

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00007f19c006e000 nid=0x3b76 runnable 

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x00007f19c0070000 nid=0x3b77 runnable 

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x00007f19c0071800 nid=0x3b78 runnable 

"GC task thread#4 (ParallelGC)" os_prio=0 tid=0x00007f19c0073800 nid=0x3b79 runnable 

"GC task thread#5 (ParallelGC)" os_prio=0 tid=0x00007f19c0075800 nid=0x3b7a runnable 

"GC task thread#6 (ParallelGC)" os_prio=0 tid=0x00007f19c0077000 nid=0x3b7d runnable 

"GC task thread#7 (ParallelGC)" os_prio=0 tid=0x00007f19c0079000 nid=0x3b7e runnable 

"VM Periodic Task Thread" os_prio=0 tid=0x00007f19c0148000 nid=0x3b88 waiting on condition 

JNI global references: 313

Answer 1

OK，原来不是bug，跟Java升级无关。这是因为 Executors.newCachedThreadPool() 使用非守护线程，导致应用程序在最后一个任务完成后一分钟内保持 Activity 状态。 (池一直在那里，但最近我们的应用程序发生变化，向它提交了一个任务，所以它变成了非空的。)

所以我需要对其调用 shutdown() 或使用答案 to this question创建一个守护进程线程池。