Java学习笔记-线程通讯 2

之前 1 用到了通过利用the Thread owned the monitor of the thread pool 去调用处于同步监听 object 的 wait 、notify 、notifyall 三个方法来实现线程通讯的执行

主要清晰当存在synchronize block 时 ，同步监听的锁的释放与否问题，锁获取可否问题

首先说Object.wait , see Java doc Object

总结为  Object 的wait 会释放锁，让其他线程竞争

而thread的 await不会，只会执行完synchronized的代码块后才释放，或者可理解成Object 的wait是一个包装后 lock 方法

The current thread must own this object's monitor.

This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. 
Thread T becomes disabled for thread scheduling purposes and lies dormant(潜伏的） until one of four things happens:

Some other thread invokes the notify method for this object and thread T happens to be arbitrarily chosen as the thread to be awakened.
Some other thread invokes the notifyAll method for this object.
Some other thread interrupts thread T.
The specified amount of real time has elapsed, more or less. If timeout is zero, however, then real time is not taken into consideration and the thread simply waits until notified.
The thread T is then （第一）removed from the wait set for this object and （第二）re-enabled for thread scheduling. It then competes in the usual manner with other threads for the right to synchronize on the object; 
once it has gained control of the object, all its synchronization claims on the object are restored to the status quo ante（as before） - that is, to the situation as of the time that the wait method was invoked. 
Thread T then returns from the invocation of the wait method. Thus, on return from the wait method, the synchronization state of the object and of thread T is exactly as it was when the wait method was invoked.
A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup（表面可能出现不明自动唤醒，）. While this will rarely occur in practice, 
applications must guard against it by testing for the condition 
that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied（while 持续判断）. In other words, waits should always occur in loops, like this one:

     synchronized (obj) {
         while (<condition does not hold>)
             obj.wait(timeout);
         ... // Perform action appropriate to condition
     }
 
(For more information on this topic, see Section 3.2.3 in Doug Lea's "Concurrent Programming in Java (Second Edition)" (Addison-Wesley, 2000), or Item 50 in Joshua Bloch's "Effective Java Programming Language Guide" (Addison-Wesley, 2001).
If the current thread is interrupted by any thread before or while it is waiting, then an InterruptedException is thrown. This exception is not thrown until the lock status of this object has been restored as described above.

Note that the wait method, as it places the current thread into the wait set for this object, unlocks only this object; any other objects on which the current thread may be synchronized remain locked while the thread waits.

This method should only be called by a thread that is the owner of this object's monitor. See the notify method for a description of the ways in which a thread can become the owner of a monitor