java notify

背景

java 的wait 和notify是一对Object上面的api,这个api需要对对象做synchronized

wait notify 需要对对象获取synchronized 锁住对象，否则需要

// -----------------------------------------------------------------------------
// Wait/Notify/NotifyAll
//
// Note: a subset of changes to ObjectMonitor::wait()
// will need to be replicated in complete_exit
void ObjectMonitor::wait(jlong millis, bool interruptible, TRAPS) {
  JavaThread* current = THREAD;

  assert(InitDone, "Unexpectedly not initialized");

  CHECK_OWNER();  // Throws IMSE if not owner.    ///////////////////////////////////////////////// 这里会判断是否有synchronized 加上同步块

  EventJavaMonitorWait event;


...
}

CHECK_OWNER 宏展开：会调研 ObjectMonitor::check_owner

// Checks that the current THREAD owns this monitor and causes an
// immediate return if it doesn't. We don't use the CHECK macro
// because we want the IMSE to be the only exception that is thrown
// from the call site when false is returned. Any other pending
// exception is ignored.
#define CHECK_OWNER()                                                  \
  do {                                                                 \
    if (!check_owner(THREAD)) {                                        \
       assert(HAS_PENDING_EXCEPTION, "expected a pending IMSE here."); \
       return;                                                         \
     }                                                                 \
  } while (false)

然后我们看ObjectMonitor::check_owner 实现：

// Returns true if the specified thread owns the ObjectMonitor.
// Otherwise returns false and throws IllegalMonitorStateException
// (IMSE). If there is a pending exception and the specified thread
// is not the owner, that exception will be replaced by the IMSE.
bool ObjectMonitor::check_owner(TRAPS) {
  JavaThread* current = THREAD;
  void* cur = owner_raw();
  assert(cur != anon_owner_ptr(), "no anon owner here");
  if (cur == current) {
    return true;
  }
  if (LockingMode != LM_LIGHTWEIGHT && current->is_lock_owned((address)cur)) {
    set_owner_from_BasicLock(cur, current);  // Convert from BasicLock* to Thread*.
    _recursions = 0;
    return true;
  }
  THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
             "current thread is not owner", false);
}

最后看ObjectMonitor::owner_raw 实现

inline void* ObjectMonitor::owner_raw() const {
  return Atomic::load(&_owner);
}

ObjectMonitor 就算monitor的实现了：

class ObjectMonitor : public CHeapObj<mtObjectMonitor> {
...
private:
  static void* anon_owner_ptr() { return reinterpret_cast<void*>(ANONYMOUS_OWNER); }

  void* volatile _owner;            // pointer to owning thread OR BasicLock
  volatile uint64_t _previous_owner_tid;  // thread id of the previous owner of the monitor
  ...
};

背景​

背景