java并发系列-monitor机制实现

volatile markOop   _header;       // displaced object header word - mark
volatile intptr_t  _count;        // reference count to prevent reclaimation/deflation
                                    // at stop-the-world time.  See deflate_idle_monitors().
                                    // _count is approximately |_WaitSet| + |_EntryList|
说明：抢占该锁的线程数 约等于 WaitSet.size + EntryList.size
volatile intptr_t  _waiters;      // number of waiting threads
volatile intptr_t  _recursions;   // recursion count, 0 for first entry
void*     volatile _object;       // backward object pointer - strong root
void *  volatile _owner;          // pointer to owning thread OR BasicLock
ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock
Thread * volatile _Responsible
  Thread * volatile _succ ;          // Heir presumptive thread - used for futile wakeup throttling
  ObjectWaiter * volatile _cxq ;    // LL of recently-arrived threads blocked on entry.
                                    // The list is actually composed of WaitNodes, acting
                                    // as proxies for Threads.
ObjectMonitor * FreeNext ;        // Free list linkage
ObjectWaiter * volatile _EntryList ;     // Threads blocked on entry or reentry.
volatile int _SpinFreq ;          // Spin 1-out-of-N attempts: success rate
volatile int _SpinClock ;
int OwnerIsThread ;               // _owner is (Thread *) vs SP/BasicLock
volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
_header	定义： volatile markOop _header; // displaced object header word - mark 说明: 　　_header是一个markOop类型，markOop就是对象头中的Mark Word
_count	定义： volatile intptr_t _count; // reference count to prevent reclaimation/deflation // at stop-the-world time. See deflate_idle_monitors(). // _count is approximately \|_WaitSet\| + \|_EntryList\| 说明：抢占该锁的线程数约等于 WaitSet.size + EntryList.size
_waiters	定义： volatile intptr_t _waiters; // number of waiting threads 说明：等待线程数
_recursions	定义： volatile intptr_t _recursions; // recursion count, 0 for first entry 说明：锁重入次数
_object	定义： void* volatile _object; // backward object pointer - strong root 说明：监视器锁寄生的对象。锁不是平白出现的，而是寄托存储于对象中
_owner	定义： void * volatile _owner; // pointer to owning thread OR BasicLock 说明：指向获得ObjectMonitor对象的线程或基础锁
_WaitSet	定义： ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor 说明：处于wait状态的线程，被加入到这个linkedList
_WaitSetLock	定义： volatile int _WaitSetLock; // protects Wait Queue - simple spinlock 说明：protects Wait Queue - simple spinlock ，保护WaitSet的一个自旋锁(monitor大锁里面的一个小锁，这个小锁用来保护_WaitSet更改)
_Responsible	定义： Thread * volatile _Responsible 说明：未知参考：https://www.jianshu.com/p/09de11d71ef8
_succ	定义： Thread * volatile _succ ; // Heir presumptive thread - used for futile wakeup throttling 说明：当锁被前一个线程释放，会指定一个假定继承者线程，但是它不一定最终获得锁。参考：https://www.jianshu.com/p/09de11d71ef8
_cxq	定义： ObjectWaiter * volatile _cxq ; // LL of recently-arrived threads blocked on entry. // The list is actually composed of WaitNodes, acting // as proxies for Threads. 说明：ContentionList 参考：https://www.jianshu.com/p/09de11d71ef8
FreeNext	定义： ObjectMonitor * FreeNext ; // Free list linkage 说明：未知
_EntryList	定义： ObjectWaiter * volatile _EntryList ; // Threads blocked on entry or reentry. 说明：未获取锁被阻塞或者被wait的线程重新进入被放入entryList中
_SpinFreq	定义： volatile int _SpinFreq ; // Spin 1-out-of-N attempts: success rate 说明：未知可能是获取锁的成功率
_SpinClock	定义： volatile int _SpinClock ; 说明：未知
OwnerIsThread	定义： int OwnerIsThread ; // _owner is (Thread *) vs SP/BasicLock 说明：当前owner是thread还是BasicLock
_previous_owner_tid	定义： volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor 说明：当前owner的线程id