SelectableChannel的register()方法和Selector的select()方法对资源的竞争问题-优快云博客

    无意中看到的, 原帖：
  http://www.oschina.net/code/snippet_246601_22883 
 

    首先,问问题的人和回答问题的人应该都没有好好的仔细看书.书中已经明确地说到：
 

 
       SelectableChannel的register(Selector selector, ...)和Selector的select()方法都会操作Selector对象的共享资源all-keys集合.
      
       SelectableChannel及Selector的实现对操作共享资源的代码块进行了同步,从而避免了对共享资源的竞争.
      
       同步机制使得一个线程执行SelectableChannel的register(Selector selctor, ...)时,
      
       不允许另一个线程同时执行Selector的select()方法,反之亦然.

     并且说明解释的也很清楚.
  
     既然这么说了,那看完书中的代码之后就应该对其进行一些改造,这样才能更好的理解程序.
  
     为了解答这里的问题,对例子稍微一些改动：

1.

2.

    然后运行程序,这时候​可以看到出现问题了：
 

     查看问题出在何处,首先执行jps查看运行的程序的pid.接下来使用jstack命令.如下：
 

    
       C:\Users\yangkun>jstack 10008
      
       2013-10-27 15:37:16
      
       Full thread dump Java HotSpot(TM) 64-Bit Server VM (23.5-b02 mixed mode):
      
       "Thread-0" prio=6 tid=0x000000000ac26800 nid=0x1dd8 waiting for monitor entry [0
      
       x000000000b25f000]
      
          java.lang.Thread.State: BLOCKED (on object monitor)
      
               at sun.nio.ch.SelectorImpl.register(Unknown Source)
      
               - waiting to lock <0x00000000eb4b3cd8> (a java.util.Collections$Unmodifi
      
       ableSet)
      
               at java.nio.channels.spi.AbstractSelectableChannel.register(Unknown Sour
      
       ce)
      
               - locked <0x00000000eb4f2210> (a java.lang.Object)
      
               at java.nio.channels.SelectableChannel.register(Unknown Source)
      
               at tcp.selector.SelectorDeadLock.accept(SelectorDeadLock.java:47)
      
               at tcp.selector.SelectorDeadLock$1.run(SelectorDeadLock.java:83)
      
       "Service Thread" daemon prio=6 tid=0x0000000008fa8000 nid=0x2a4c runnable [0x000
      
       0000000000000]
      
          java.lang.Thread.State: RUNNABLE
      
       "C2 CompilerThread1" daemon prio=10 tid=0x0000000008f9c000 nid=0x29b0 waiting on
      
        condition [0x0000000000000000]
      
          java.lang.Thread.State: RUNNABLE
      
       "C2 CompilerThread0" daemon prio=10 tid=0x0000000008f9a000 nid=0x29ac waiting on
      
        condition [0x0000000000000000]
      
          java.lang.Thread.State: RUNNABLE
      
       "Attach Listener" daemon prio=10 tid=0x0000000008f99000 nid=0x29b4 waiting on co
      
       ndition [0x0000000000000000]
      
          java.lang.Thread.State: RUNNABLE
      
       "Signal Dispatcher" daemon prio=10 tid=0x0000000008f92000 nid=0x2a48 runnable [0
      
       x0000000000000000]
      
          java.lang.Thread.State: RUNNABLE
      
       "Finalizer" daemon prio=8 tid=0x00000000025a6000 nid=0x2a40 in Object.wait() [0x
      
       000000000a37f000]
      
          java.lang.Thread.State: WAITING (on object monitor)
      
               at java.lang.Object.wait(Native Method)
      
               - waiting on <0x00000000eb405798> (a java.lang.ref.ReferenceQueue$Lock)
      
               at java.lang.ref.ReferenceQueue.remove(Unknown Source)
      
               - locked <0x00000000eb405798> (a java.lang.ref.ReferenceQueue$Lock)
      
               at java.lang.ref.ReferenceQueue.remove(Unknown Source)
      
               at java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)
      
       "Reference Handler" daemon prio=10 tid=0x000000000259f000 nid=0x2a3c in Object.w
      
       ait() [0x000000000a1ef000]
      
          java.lang.Thread.State: WAITING (on object monitor)
      
               at java.lang.Object.wait(Native Method)
      
               - waiting on <0x00000000eb405320> (a java.lang.ref.Reference$Lock)
      
               at java.lang.Object.wait(Object.java:503)
      
               at java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)
      
               - locked <0x00000000eb405320> (a java.lang.ref.Reference$Lock)
      
       "main" prio=6 tid=0x000000000264c800 nid=0x25a8 runnable [0x000000000296e000]
      
          java.lang.Thread.State: RUNNABLE
      
               at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll0(Native Method)
      
               at sun.nio.ch.WindowsSelectorImpl$SubSelector.poll(Unknown Source)
      
               at sun.nio.ch.WindowsSelectorImpl$SubSelector.access$400(Unknown Source)
      
               at sun.nio.ch.WindowsSelectorImpl.doSelect(Unknown Source)
      
               at sun.nio.ch.SelectorImpl.lockAndDoSelect(Unknown Source)
      
               - locked <0x00000000eb4b3d58> (a sun.nio.ch.Util$2)
      
               - locked <0x00000000eb4b3cd8> (a java.util.Collections$UnmodifiableSet)
      
               - locked <0x00000000eb4b3768> (a sun.nio.ch.WindowsSelectorImpl)
      
               at sun.nio.ch.SelectorImpl.select(Unknown Source)
      
               at sun.nio.ch.SelectorImpl.select(Unknown Source)
      
               at tcp.selector.SelectorDeadLock.service(SelectorDeadLock.java:62)
      
               at tcp.selector.SelectorDeadLock.main(SelectorDeadLock.java:89)
      
       "VM Thread" prio=10 tid=0x0000000008ef2800 nid=0x2a38 runnable
      
       "GC task thread#0 (ParallelGC)" prio=6 tid=0x00000000024f3000 nid=0x2144 runnabl
      
       e
      
       "GC task thread#1 (ParallelGC)" prio=6 tid=0x00000000024f5000 nid=0x2344 runnabl
      
       e
      
       "GC task thread#2 (ParallelGC)" prio=6 tid=0x00000000024f6800 nid=0x2318 runnabl
      
       e
      
       "GC task thread#3 (ParallelGC)" prio=6 tid=0x00000000024f8800 nid=0x22c4 runnabl
      
       e
      
       "VM Periodic Task Thread" prio=10 tid=0x0000000008fb1800 nid=0x249c waiting on c
      
       ondition
      
       JNI global references: 125

   程序会一致阻塞而无法继续执行.
 

SelectableChannel的register()方法和Selector的select()方法对资源的竞争问题

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