synchronized, wait, notify

[Aaron Anders]

hello folks, i'm confused with the relationship between synchronzied keyword and wait()/notify()/notifyall()...

does the internal implementation of synchronized method/statement make use of wait()/notify()/notifyall()?

i.e. does

    synchronized (this)
    {
        // ...
    }

same as

    this.wait()
    {
        // ...
    }
    this.notifyall()

?

[Peter den Haan]

Originally posted by Aaron Anders:
does the internal implementation of synchronized method/statement make use of wait()/notify()/notifyall()?

No. To the contrary, wait/notify are built upon the synchronized statement in the sense that you must own a monitor lock (i.e. be inside a synchronized method or block) before you can call wait() or notify() on an object.
Synchronization is a way to ensure that some operations are atomic w.r.t. other threads, in other words, that only one thread can execute the synchronized method(s) or block(s) at any given time. Inside a synchronized method/block, the thread is the exclusive owner of the object's monitor lock.
The wait/notify methods, on the other hand, are a way to co-ordinate actions between different threads. They allow a thread to release its monitor lock and wait() for something to happen, or to notify() waiting threads that something happened.
- Peter

[Aaron Anders]

thanks for the reply.
i have one more question
while reading JDK doc, it says "wait() ... The current thread must own this object's monitor.", what will happen if i wait for object other than i've been synchronized for?
i.e.

  synchronized(a)
  {
    b.wait();
    // ...
    b.notifyall();
  } 

just curious...

[Jim Yingst]

It throws a ProgrammerFailedToReadAPIException.