How to build a exclusive Lock

阻塞lock的基本流程

if(cas(0,acquire))

setExclusiveOwnerThread

else if(current==getExclusiveOnwerThread) {

     setState(c+acquires)

}

addWaiter

park

........................

for(;;) {

p = node.predecessor

if(p==head&&tryAcquire(arg)){

setHead(node)

return

}

park

}

 

阻塞release的基本流程

if(current!=getExclusiveOnwerThread){

IllegalMonitorStateException

}

if(c == 0){

setExclusive(null)

free = true

}

setState(c)

return free

unparkSuccessor(LockSupport.unpark(thread))

 

非阻塞lock的基本流程

if(cas(0,acquire)) 

     setExclusiveOwnerThread   true

else if(current==getExclusiveOwnerThread)

     setState(c+acquire)    true

false

 

非阻塞的release的基本流程

与阻塞的release流程相同

 

 

阻塞共享lock的基本流程

tryAcquireShared(acquires){

for(;;) {

remaining = state-acquires

if(remaining<0 || CAS(state,remaining))

return remaining

}

}

 

 

if(tryAcquireShared(arg)<0){

     node = addWaiter(Node.SHARED)

     for(;;) {

p = node.predecessor

propagate = tryAcquireShared(arg)

if(p==head&&propagate>=0){

setHead(node)

if(propagate>0||next==null||next.isShared())//如果还有剩余，继续唤醒接下来一个节点

     doReleaseShared() 

return

}

park

     }

}

 

阻塞共享release的基本流程

tryReleaseShared(acquires){

for(;;){

     if(cas(state,state+acquires)) 

          return true

}

 

}

if(tryReleaseShared(acquires)) {

     unparkSuccessor(h)

}

 

 

 

 

 

共享lock的基本模式

覆盖tryAcquireShared方法

for(;;) {
     if(state-acquire<0) {
          false
     }
     if(cas(state,state-acquires)) {
          true
     }
}

 

共享lock的release的基本模式

覆盖tryReleaseShared方法

for(;;) {
     if(cas(state,state+acquires)) {
          true
     }
}

 排它lock的基本模式

覆盖tryAcquire方法

if(state==0) {
     if(cas(state, state+acquire)) {
          setExclusiveOwnerThread(current)
              return true
     }
} else if(current==getExclusiveOwnerThread) {
     if(cas(state, state+acquire)) {
          return true
     }
}
return flase

 排它lock的release基本模式

覆盖tryRelease方法

if(current != getExclusiveThread) {
     throw new IllegalMonitorStateException()
}
nextc = state-release
if(nextc == 0) {
     setState(nextc)
     setExclusiveOwnerThread(current)
     return true
} else {
     setState(nextc)
     return false
}