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

[Hugh Nimmo-Smith]

I disagree because Scheduler.queue(int number) should block

eg.

class Scheduler {

  private int number = 0;

  void queue(int n)
  {
    // if it isnt time for n then block
    while (number < n) wait();
  }

  synchronized void next()
  {
    number++;
    notifyAll(); // notify other waiting threads
  }
}

That was my interpretation of the question

Hugh

> -----Original Message-----
> From: William R Sowerbutts [mailto:will@sowerbutts.com]
> Sent: 03 May 2000 11:13
> To: Hugh Nimmo-Smith
> Cc: M.Y.W.Y.B.; cst-1b@srcf.ucam.org
> Subject: Re: [Cst-1b] CST1-b Question: Java 98/4/3
> 
> 
> 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
> >>
> >>
> >> _______________________________________________
> >> CST-1B mailing list
> >> CST-1B@srcf.ucam.org
> >> http://www.srcf.ucam.org/mailman/listinfo/cst-1b
> >>
> >
> >
> >
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> 
> 
> _________________________________________________________________________
> William R Sowerbutts (BtG)                            will@sowerbutts.com
> Coder / Guru / Nrrrd                                http://sowerbutts.com
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>