[Cst-1b] CST1-b Question: Java 98/4/3

[William R Sowerbutts]

I would argue that this IS very different. If one thread calls put() when the
buffer already contains a value, then this thread will eat up any available
CPU runtime until the buffer become empty. Likewise, calling get() on an empty
buffer will eat CPU runtime quite happily until the buffer is full.

Martin's solution was very much better.



On Wed, May 03, 2000 at 09:29:21AM +0100, Hugh Nimmo-Smith wrote:
>My solution was something like this... not very different but possibly
>safer:
>
>class SyncBuffer {
>
>  int value; // value in buffer
>
>  boolean valid; // is there a value in teh buffer
>
>  TicketMachine m = new TicketMachine();
>  Scheduler s = new Scheduler();
>
>  void put(int v)
>  {
>    boolean put = false; // have we put are value into buffer yet??
>
>    while (!put)
>    {
>      int number = m.turn();
>      s.queue(number);
>      // we now have lock on object
>
>      // if there isn't a value in buffer then put our value into buffer
>      if (!valid) {
>
>        // put value in to buffer
>        value = v;
>
>        // remember we have put value
>        put = true;
>
>        // mark buffer as holding a value
>        valid = true;
>      }
>
>      s.next(); // notify other waiting threads
>    }
>  }
>
>  int get()
>  {
>    int result;
>    boolean got_result = false; // have we got a value from buffer yet?
>
>    while (!got_result)
>    {
>      int number = m.term();
>      s.queue(number);
>      // we now have lock on object
>
>      // if there is a value in the buffer then get it...
>      if (valid) {
>
>        // get the result
>        result = value;
>
>        // set the buffer to not contain a value
>        valid = false;
>
>        // remeber that we have got a value
>        got_result = true;
>      }
>    }
>  }
>}
>> -----Original Message-----
>> From: cst-1b-admin@srcf.ucam.org [mailto:cst-1b-admin@srcf.ucam.org]On
>> Behalf Of M.Y.W.Y.B.
>> Sent: 02 May 2000 22:03
>> To: cst-1b@srcf.ucam.org
>> Subject: [Cst-1b] CST1-b Question: Java 98/4/3
>>
>>
>> CST 98/4/3
>> http://www.cl.cam.ac.uk/tripos/y1998p4q3.pdf
>>
>> Hi!
>>
>> Has anyone solved the last part of the question in 98/4/3?
>> "Show how a synchronised buffer holding a single value could be
>> implemented
>> using this new scheme".
>>
>> I assume that you are not allowed to use "synchronized", "wait()",
>> "notify()" etc but only TicketMachine and Scheduler methods. But how?
>>
>> Thanks
>>
>> Moritz
>>
>>
>> _______________________________________________
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>> CST-1B@srcf.ucam.org
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>>
>
>
>
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_________________________________________________________________________
William R Sowerbutts (BtG)                            will@sowerbutts.com
Coder / Guru / Nrrrd                                http://sowerbutts.com
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