深入分析JVM中執行緒的建立和執行原理 （future）
阿新 • • 發佈：2019-01-06
在JVM中除了應用執行緒，還有其他的一些執行緒用於支援JVM的執行，這些執行緒可以被劃分為以下幾類：
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VM Thread：負責JVM在安全點內的各種操作，這些操作（諸如自動記憶體管理、取消偏向鎖、執行緒dump、執行緒掛起等等）在執行過程中需要JVM處於這樣一個狀態——堆的內容不會被改變，這種狀態在JVM裡叫做安全點（safe-point）。
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Periodic task thread：這個執行緒負責響應定時觸發的事件（例如：中斷），用來執行一些定時操作。
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GC thread：這些執行緒負責JVM裡的垃圾收集活動；
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Compiler threads：這些執行緒負責在執行時將位元組碼編譯為原生代碼；
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Singal dispatcher thread：這些執行緒負責響應外部發給當前JVM程序的訊號，並通過呼叫JVM內的其他執行緒。
我們再用jstack命令做一次執行緒dump，就可以得到如下內容：
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.151-b12 mixed mode):
"RMI TCP Connection(5)-192.168.0.139" #17 daemon prio=9 os_prio=31 tid=0x00007fba7c830800 nid=0x5c03 runnable [0x000070000f740000]
java.lang.Thread.State: RUNNABLE
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
at java.net.SocketInputStream.read(SocketInputStream.java:171)
at java.net.SocketInputStream.read(SocketInputStream.java:141)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:246)
at java.io.BufferedInputStream.read(BufferedInputStream.java:265)
- locked <0x000000076f590708> (a java.io.BufferedInputStream)
at java.io.FilterInputStream.read(FilterInputStream.java:83)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:550)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$3/745402377.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
"RMI TCP Connection(2)-192.168.0.139" #16 daemon prio=9 os_prio=31 tid=0x00007fba7e0b0000 nid=0xa403 in Object.wait() [0x000070000f63c000]
java.lang.Thread.State: TIMED_WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x000000076f580878> (a com.sun.jmx.remote.internal.ArrayNotificationBuffer)
at com.sun.jmx.remote.internal.ArrayNotificationBuffer.fetchNotifications(ArrayNotificationBuffer.java:449)
- locked <0x000000076f580878> (a com.sun.jmx.remote.internal.ArrayNotificationBuffer)
at com.sun.jmx.remote.internal.ArrayNotificationBuffer$ShareBuffer.fetchNotifications(ArrayNotificationBuffer.java:227)
at com.sun.jmx.remote.internal.ServerNotifForwarder.fetchNotifs(ServerNotifForwarder.java:274)
at javax.management.remote.rmi.RMIConnectionImpl$4.run(RMIConnectionImpl.java:1270)
at javax.management.remote.rmi.RMIConnectionImpl$4.run(RMIConnectionImpl.java:1268)
at javax.management.remote.rmi.RMIConnectionImpl.fetchNotifications(RMIConnectionImpl.java:1274)
at sun.reflect.GeneratedMethodAccessor62.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:357)
at sun.rmi.transport.Transport$1.run(Transport.java:200)
at sun.rmi.transport.Transport$1.run(Transport.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:196)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler$$Lambda$3/745402377.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
"JMX server connection timeout 15" #15 daemon prio=9 os_prio=31 tid=0x00007fba80014800 nid=0xa503 in Object.wait() [0x000070000f53b000]
java.lang.Thread.State: TIMED_WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x000000076f5887f8> (a [I)
at com.sun.jmx.remote.internal.ServerCommunicatorAdmin$Timeout.run(ServerCommunicatorAdmin.java:168)
- locked <0x000000076f5887f8> (a [I)
at java.lang.Thread.run(Thread.java:748)
"RMI Scheduler(0)" #14 daemon prio=9 os_prio=31 tid=0x00007fba7c805800 nid=0xa603 waiting on condition [0x000070000f438000]
java.lang.Thread.State: TIMED_WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x000000076f598188> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitNanos(AbstractQueuedSynchronizer.java:2078)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:1093)
at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(ScheduledThreadPoolExecutor.java:809)
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 java.lang.Thread.run(Thread.java:748)
"RMI TCP Accept-0" #12 daemon prio=9 os_prio=31 tid=0x00007fba7d906000 nid=0xa803 runnable [0x000070000f232000]
java.lang.Thread.State: RUNNABLE
at java.net.PlainSocketImpl.socketAccept(Native Method)
at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:409)
at java.net.ServerSocket.implAccept(ServerSocket.java:545)
at java.net.ServerSocket.accept(ServerSocket.java:513)
at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(LocalRMIServerSocketFactory.java:52)
at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(TCPTransport.java:400)
at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(TCPTransport.java:372)
at java.lang.Thread.run(Thread.java:748)
"Attach Listener" #10 daemon prio=9 os_prio=31 tid=0x00007fba7d865800 nid=0xa903 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Service Thread" #9 daemon prio=9 os_prio=31 tid=0x00007fba7d803000 nid=0x3903 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C1 CompilerThread3" #8 daemon prio=9 os_prio=31 tid=0x00007fba7e002000 nid=0x3803 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread2" #7 daemon prio=9 os_prio=31 tid=0x00007fba80000000 nid=0x3703 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread1" #6 daemon prio=9 os_prio=31 tid=0x00007fba7d82d800 nid=0x3e03 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #5 daemon prio=9 os_prio=31 tid=0x00007fba7c020000 nid=0x3f03 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fba7c01e800 nid=0x3403 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fba7f022000 nid=0x4903 in Object.wait() [0x000070000e917000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x000000076f5a0600> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
- locked <0x000000076f5a0600> (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" #2 daemon prio=10 os_prio=31 tid=0x00007fba7c01d800 nid=0x4b03 in Object.wait() [0x000070000e814000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x000000076f5983e8> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x000000076f5983e8> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
"main" #1 prio=5 os_prio=31 tid=0x00007fba7f000000 nid=0x2303 runnable [0x000070000ddf6000]
java.lang.Thread.State: RUNNABLE
at GcExample.main(GcExample.java:9)
"VM Thread" os_prio=31 tid=0x00007fba7c01b000 nid=0x2f03 runnable
"GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fba7c007000 nid=0x2007 runnable
"GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fba7d804800 nid=0x2a03 runnable
"GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fba7c007800 nid=0x5303 runnable
"GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fba7f800000 nid=0x2c03 runnable
"GC task thread#4 (ParallelGC)" os_prio=31 tid=0x00007fba7d805000 nid=0x5103 runnable
"GC task thread#5 (ParallelGC)" os_prio=31 tid=0x00007fba7c013800 nid=0x5003 runnable
"GC task thread#6 (ParallelGC)" os_prio=31 tid=0x00007fba7f001000 nid=0x4e03 runnable
"GC task thread#7 (ParallelGC)" os_prio=31 tid=0x00007fba7c014000 nid=0x4c03 runnable
"VM Periodic Task Thread" os_prio=31 tid=0x00007fba7d858800 nid=0x3a03 waiting on condition
JNI global references: 295
OK，從上面這個dump檔案中，可以找到Periodic Task Thread、GC Thread、VM Thread、Compiler Thread的身影了。