try了那么多次lock，接下来看下TryLock:
int ObjectMonitor::TryLock (Thread * Self) { for (;;) { void * own = _owner ; if (own != NULL) return 0 ;//如果有线程还拥有着重量级锁，退出 //CAS操作将_owner修改为当前线程，操作成功return>0 if (Atomic::cmpxchg_ptr (Self, &_owner, NULL) == NULL) { return 1 ; } //CAS更新失败return<0 if (true) return -1 ; } }重量级锁获取入口流程图：
重量级锁的出口：
void ATTR ObjectMonitor::exit(TRAPS) { Thread * Self = THREAD ; if (THREAD != _owner) { if (THREAD->is_lock_owned((address) _owner)) { _owner = THREAD ; _recursions = 0 ; OwnerIsThread = 1 ; } else { TEVENT (Exit - Throw IMSX) ; if (false) { THROW(vmSymbols::java_lang_IllegalMonitorStateException()); } return; } } if (_recursions != 0) { _recursions--; // 如果_recursions次数不为0.自减 TEVENT (Inflated exit - recursive) ; return ; } if ((SyncFlags & 4) == 0) { _Responsible = NULL ; } for (;;) { if (Knob_ExitPolicy == 0) { OrderAccess::release_store_ptr (&_owner, NULL) ; // drop the lock OrderAccess::storeload() ; if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) { TEVENT (Inflated exit - simple egress) ; return ; } TEVENT (Inflated exit - complex egress) ; if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) { return ; } TEVENT (Exit - Reacquired) ; } else { if ((intptr_t(_EntryList)|intptr_t(_cxq)) == 0 || _succ != NULL) { OrderAccess::release_store_ptr (&_owner, NULL) ; OrderAccess::storeload() ; if (_cxq == NULL || _succ != NULL) { TEVENT (Inflated exit - simple egress) ; return ; } if (Atomic::cmpxchg_ptr (THREAD, &_owner, NULL) != NULL) { TEVENT (Inflated exit - reacquired succeeded) ; return ; } TEVENT (Inflated exit - reacquired failed) ; } else { TEVENT (Inflated exit - complex egress) ; } } ObjectWaiter * w = NULL ; int QMode = Knob_QMode ; if (QMode == 2 && _cxq != NULL) { /** *模式2:cxq队列的优先权大于EntryList，直接从cxq队列中取出一个线程结点，准备唤醒 **/ w = _cxq ; ExitEpilog (Self, w) ; return ; } if (QMode == 3 && _cxq != NULL) { /** *模式3:将cxq队列插入到_EntryList尾部 **/ w = _cxq ; for (;;) { //CAS操作取出cxq队列首结点 ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ; if (u == w) break ; w = u ; //更新w，自旋 } ObjectWaiter * q = NULL ; ObjectWaiter * p ; for (p = w ; p != NULL ; p = p->_next) { guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ; p->TState = ObjectWaiter::TS_ENTER ; //改变ObjectWaiter状态 //下面两句为cxq队列反向构造一条链，即将cxq变成双向链表 p->_prev = q ; q = p ; } ObjectWaiter * Tail ; //获得_EntryList尾结点 for (Tail = _EntryList ; Tail != NULL && Tail->_next != NULL ; Tail = Tail->_next) ; if (Tail == NULL) { _EntryList = w ;//_EntryList为空，_EntryList=w } else { //将w插入_EntryList队列尾部 Tail->_next = w ; w->_prev = Tail ; } } if (QMode == 4 && _cxq != NULL) { /** *模式四：将cxq队列插入到_EntryList头部 **/ w = _cxq ; for (;;) { ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ; if (u == w) break ; w = u ; } ObjectWaiter * q = NULL ; ObjectWaiter * p ; for (p = w ; p != NULL ; p = p->_next) { guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ; p->TState = ObjectWaiter::TS_ENTER ; p->_prev = q ; q = p ; } if (_EntryList != NULL) { //q为cxq队列最后一个结点 q->_next = _EntryList ; _EntryList->_prev = q ; } _EntryList = w ; } w = _EntryList ; if (w != NULL) { ExitEpilog (Self, w) ;//从_EntryList中唤醒线程 return ; } w = _cxq ; if (w == NULL) continue ; //如果_cxq和_EntryList队列都为空，自旋 for (;;) { //自旋再获得cxq首结点 ObjectWaiter * u = (ObjectWaiter *) Atomic::cmpxchg_ptr (NULL, &_cxq, w) ; if (u == w) break ; w = u ; } /** *下面执行的是：cxq不为空，_EntryList为空的情况 **/ if (QMode == 1) {//结合前面的代码，如果QMode == 1，_EntryList不为空，直接从_EntryList中唤醒线程 // QMode == 1 : drain cxq to EntryList, reversing order // We also reverse the order of the list. ObjectWaiter * s = NULL ; ObjectWaiter * t = w ; ObjectWaiter * u = NULL ; while (t != NULL) { guarantee (t->TState == ObjectWaiter::TS_CXQ, "invariant") ; t->TState = ObjectWaiter::TS_ENTER ; //下面的操作是双向链表的倒置 u = t->_next ; t->_prev = u ; t->_next = s ; s = t; t = u ; } _EntryList = s ;//_EntryList为倒置后的cxq队列 } else { // QMode == 0 or QMode == 2 _EntryList = w ; ObjectWaiter * q = NULL ; ObjectWaiter * p ; for (p = w ; p != NULL ; p = p->_next) { guarantee (p->TState == ObjectWaiter::TS_CXQ, "Invariant") ; p->TState = ObjectWaiter::TS_ENTER ; //构造成双向的 p->_prev = q ; q = p ; } } if (_succ != NULL) continue; w = _EntryList ; if (w != NULL) { ExitEpilog (Self, w) ; //从_EntryList中唤醒线程 return ; } } }