JVM線程

時間 2019-11-21

標籤 jvm 線程欄目 Java 简体版

原文原文鏈接

JVM線程

參考《Java內存泄漏分析系列》html

dump文件結構

屬性含義java

"http-nio-9090-exec-2"      線程名稱
prio                        優先級
os_prio                     系統優先級
tid                         虛擬機中的Java線程id
nid                         線程在操做系統中的id
[0x00007f5822648000]        線程棧起始內存地址

Identifier & Version

2018-06-15 01:12:34
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.144-b01 mixed mode):

Application Threads

"http-nio-9090-exec-2" #38 daemon prio=5 os_prio=0 tid=0x00007f592b133800 nid=0xacc6 waiting on condition [0x00007f5822648000]
   java.lang.Thread.State: WAITING (parking)
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for  <0x000000076b27c218> (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 org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:103)
	at org.apache.tomcat.util.threads.TaskQueue.take(TaskQueue.java:31)
	at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)

VM Threads

JVM 內部運行線程介紹linux

VM Thread，負責建立其它全部線程，並經過自輪詢VMOperationQueue，按照優先級執行VM_Operation，例如ThreadDump、CMS_Initial_Mark。apache

"VM Thread" os_prio=0 tid=0x00007f59283c6000 nid=0xac91 runnable

Attach Listener，負責處理JVM外部的命令，如jstack，在第一次執行JVM命令時啓動。windows

"Attach Listener" #54 daemon prio=9 os_prio=0 tid=0x00007f589c001000 nid=0xae90 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

Signal Dispatcher，負責分發Attach Listener接收到的命令，第一次分發時啓動。tomcat

"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007f5928405000 nid=0xac94 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

DestroyJavaVM，負責卸載JVM。架構

"DestroyJavaVM" #52 prio=5 os_prio=0 tid=0x00007f5928008800 nid=0xac78 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

Service Thread，用於啓動服務的線程。app

"Service Thread" #20 daemon prio=9 os_prio=0 tid=0x00007f5928431800 nid=0xaca4 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

CompilerThread，實時編譯裝卸class，可能會形成CPU抖動。jvm

"C1 CompilerThread14" #19 daemon prio=9 os_prio=0 tid=0x00007f5928426000 nid=0xaca3 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

Finalizer，負責在垃圾回收前調用對象的finalize()方法。JVM將失去引用的對象包裝成Finalizer對象（Reference的實現），放入ReferenceQueue，由Finalizer線程處理。socket

"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007f59283d2000 nid=0xac93 in Object.wait() [0x00007f58ddedd000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000068782bac0> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
	- locked <0x000000068782bac0> (a java.lang.ref.ReferenceQueue$Lock)
	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164)
	at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)

Reference Handler，優先級最高，負責處理引用對象自己的垃圾回收問題。

"Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007f59283cd800 nid=0xac92 in Object.wait() [0x00007f58ddfde000]
   java.lang.Thread.State: WAITING (on object monitor)
	at java.lang.Object.wait(Native Method)
	- waiting on <0x000000068782bab0> (a java.lang.ref.Reference$Lock)
	at java.lang.Object.wait(Object.java:502)
	at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
	- locked <0x000000068782bab0> (a java.lang.ref.Reference$Lock)
	at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)

GC Thread

GC task thread，GC線程，建立後會一直複用，邏輯CPU不大於8時，線程數量爲CPU數，不然爲8 + ( ncpus - 8 ) * 5/8，線程數邏輯。

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007f592801e000 nid=0xac79 runnable

unsigned int Abstract_VM_Version::calc_parallel_worker_threads() {
  return nof_parallel_worker_threads(5, 8, 8);
}

unsigned int Abstract_VM_Version::nof_parallel_worker_threads(
                                                      unsigned int num,
                                                      unsigned int den,
                                                      unsigned int switch_pt) {
  if (FLAG_IS_DEFAULT(ParallelGCThreads)) {
    assert(ParallelGCThreads == 0, "Default ParallelGCThreads is not 0");
    // For very large machines, there are diminishing returns
    // for large numbers of worker threads.  Instead of
    // hogging the whole system, use a fraction of the workers for every
    // processor after the first 8.  For example, on a 72 cpu machine
    // and a chosen fraction of 5/8
    // use 8 + (72 - 8) * (5/8) == 48 worker threads.
    unsigned int ncpus = (unsigned int) os::initial_active_processor_count();
    return (ncpus <= switch_pt) ?
           ncpus :
          (switch_pt + ((ncpus - switch_pt) * num) / den);
  } else {
    return ParallelGCThreads;
  }
}