Object.wait理解

wait注釋：

public final void wait(long timeout)
                throws InterruptedException
Causes the current thread to wait until either another thread invokes the notify() method or the notifyAll() method for this object, or a specified amount of time has elapsed.
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 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 removed from the wait set for this object and 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 - 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. 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. 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.

Parameters:
timeout - the maximum time to wait in milliseconds.
Throws:
IllegalArgumentException - if the value of timeout is negative.
IllegalMonitorStateException - if the current thread is not the owner of the object's monitor.
InterruptedException - if any thread interrupted the current thread before or while the current thread was waiting for a notification. The interrupted status of the current thread is cleared when this exception is thrown.

有以上注釋可以總結(jié)出

• 當(dāng)一個線程執(zhí)行一個Object的wait方法后炕置，只有此object調(diào)用notify或者notifyAll方法喚醒。
• 當(dāng)前線程必須只有此Object的鎖（monitor）椰拒，所以wait方法必須在同步塊中莫其。
• 當(dāng)前線程執(zhí)行一個Object的wait方法后，當(dāng)前線程將不在持有此Object的鎖（monitor）耸三。
• 喚醒wait有四種方式：
  • 調(diào)用notify方法
  • 調(diào)用notifyAll方法
  • 通過線程阻斷（interrupts）
  • 設(shè)置wait方法的喚醒時間
• wait線程乱陡，可能出現(xiàn)“假喚醒”（spurious wakeup），應(yīng)該加條件控制仪壮。