Java中的默认线程

Question

如果在代码中没有用户创建线程，则在调用jvm时会启动多少个默认线程？我已经知道2个线程将开始，这些都是

1）主线程（非守护线程）

2）垃圾收集器（守护线程）

Answer 1

如果您安装了JDK，则可以使用位于bin（Windows）目录中的jvisualvm或jconsole（旧版本的Java）。

该工具将允许您查看所有线程及其详细信息。

附上截图。

Answer 2

问题的答案取决于你的JVM。在矿山，无操作Java程序会导致以下主题：

2011-04-11 10:25:44 
Full thread dump Java HotSpot(TM) 64-Bit Server VM (19.1-b02 mixed mode): 

"Attach Listener" daemon prio=10 tid=0x0000000040222000 nid=0x606a waiting on condition [0x0000000000000000] 
    java.lang.Thread.State: RUNNABLE 

    Locked ownable synchronizers: 
    - None 

"Low Memory Detector" daemon prio=10 tid=0x0000000040211000 nid=0x6046 runnable [0x0000000000000000] 
    java.lang.Thread.State: RUNNABLE 

    Locked ownable synchronizers: 
    - None 

"CompilerThread1" daemon prio=10 tid=0x00007f80d0004000 nid=0x6045 waiting on condition [0x0000000000000000] 
    java.lang.Thread.State: RUNNABLE 

    Locked ownable synchronizers: 
    - None 

"CompilerThread0" daemon prio=10 tid=0x00007f80d0001000 nid=0x6044 waiting on condition [0x0000000000000000] 
    java.lang.Thread.State: RUNNABLE 

    Locked ownable synchronizers: 
    - None 

"Signal Dispatcher" daemon prio=10 tid=0x000000004020d800 nid=0x6043 runnable [0x0000000000000000] 
    java.lang.Thread.State: RUNNABLE 

    Locked ownable synchronizers: 
    - None 

"Finalizer" daemon prio=10 tid=0x00000000401eb000 nid=0x6042 in Object.wait() [0x00007f80d6053000] 
    java.lang.Thread.State: WAITING (on object monitor) 
    at java.lang.Object.wait(Native Method) 
    - waiting on <0x00000000eb561300> (a java.lang.ref.ReferenceQueue$Lock) 
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:118) 
    - locked <0x00000000eb561300> (a java.lang.ref.ReferenceQueue$Lock) 
    at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:134) 
    at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159) 

    Locked ownable synchronizers: 
    - None 

"Reference Handler" daemon prio=10 tid=0x00000000401e9000 nid=0x6041 in Object.wait() [0x00007f80d6154000] 
    java.lang.Thread.State: WAITING (on object monitor) 
    at java.lang.Object.wait(Native Method) 
    - waiting on <0x00000000eb5611d8> (a java.lang.ref.Reference$Lock) 
    at java.lang.Object.wait(Object.java:485) 
    at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:116) 
    - locked <0x00000000eb5611d8> (a java.lang.ref.Reference$Lock) 

    Locked ownable synchronizers: 
    - None 

"main" prio=10 tid=0x0000000040184800 nid=0x603b runnable [0x00007f80db081000] 
    java.lang.Thread.State: RUNNABLE 
    at c.main(c.java:1) 

    Locked ownable synchronizers: 
    - None 

"VM Thread" prio=10 tid=0x00000000401e2000 nid=0x6040 runnable 

"GC task thread#0 (ParallelGC)" prio=10 tid=0x0000000040197800 nid=0x603c runnable 

"GC task thread#1 (ParallelGC)" prio=10 tid=0x0000000040199800 nid=0x603d runnable 

"GC task thread#2 (ParallelGC)" prio=10 tid=0x000000004019b800 nid=0x603e runnable 

"GC task thread#3 (ParallelGC)" prio=10 tid=0x000000004019d000 nid=0x603f runnable 

"VM Periodic Task Thread" prio=10 tid=0x000000004021c000 nid=0x6047 waiting on condition 

您可以看到自己与jstack -l <pid>。