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)){

[blockquote]setHead(node)

return[/blockquote]

} 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
}

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