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Diffrence Between Notify & NotifyAll  RSS feed

 
Sathish Kumar Govindan
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Posts: 18
Spring
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Hello group,

I know that its a very lame question to ask experts like you but still
i cannot help myself asking the question that "What is the Diffrence
Between Notify & NotifyAll
" method in the Object Class.

Well so far my search on the Internet reveals
that 'notify()' method wakes up a single thread waiting on the object
and passes the control of the monitor to it. So far so good and for
'notifyAll()' it says that its will wake up all the threads waiting on the object and will select a thread to pass control to it. Well as per
me during that period the unselected thread will again go back to sleep
in the JVM scheduler list and they will need yet another call to
Notifty (or NotifyAll) in order to wake them up. So, as far as i see
there is no diffrence between notify & notifyall as they both will
result in waking up a single thread waiting on the Object.

If above assertions are indeed true than why to have two diffrent
methods.

Thanks,
Sathish Kumar.G
 
Nitesh Kant
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Posts: 1638
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Satish: 'notifyAll()' it says that its will wake up all the threads waiting on the object and will select a thread to pass control to it

It is partly correct, notifyAll() will notify all the threads and after that all the threads will contest for the monitor lock. The thread that gets the monitor lock will start the work and the rest will be waiting for the monitor lock.
The above difference is pretty big as the threads waiting for monitor will not require a notify() call to start processing but will start processing as soon as they get the monitor lock.
If you take the thread dump and see the state of the threads (although getting this dump at the correct time is somewhat tough),
  • In case of notify() only one thread will get to the RUNNING state and other will be in WAIT state
  • In case of notifyAll() only one thread will get to the RUNNING state and other will be in BLOCKED state

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    Sathish Kumar Govindan
    Greenhorn
    Posts: 18
    Spring
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    Hi Nitesh ,
    Thanks dude... now i am clear about the concept......... your answer is pretty cool


    with thanks,
    G.sathish kumar.
     
    Rahul Sudip Bose
    Ranch Hand
    Posts: 637
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    Nitesh Kant wrote:
    If you take the thread dump and see the state of the threads (although getting this dump at the correct time is somewhat tough)


    What is the "thread dump" and what are its uses ? How can i get it ?

     
    Anantha Sharma
    Ranch Hand
    Posts: 43
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    a thread dump is like the stacktrace but only specific to the thread, its state & where in the program its running, much like a program counter.

    a thread dump is a snapshot of exactly what's executing at a moment in time.

    you can view the thread dump by using an app called jConsole, this comes bundled with java it can be found in <<JAVA_HOME>>\bin\ folder.

    refer to Sun's documentation on how to use this application.
     
    It is sorta covered in the JavaRanch Style Guide.
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