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

[Hugh Nimmo-Smith]

I meant I dsagree with the eating CPU time bit... Martin's solution is
slick...

Hugh

> -----Original Message-----
> From: cst-1b-admin@srcf.ucam.org [mailto:cst-1b-admin@srcf.ucam.org]On
> Behalf Of Hugh Nimmo-Smith
> Sent: 03 May 2000 12:51
> To: William R Sowerbutts
> Cc: M.Y.W.Y.B.; cst-1b@srcf.ucam.org
> Subject: Re: [Cst-1b] CST1-b Question: Java 98/4/3
>
>
> 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
> > >>
> > >
> > >
> > >
> > >_______________________________________________
> > >CST-1B mailing list
> > >CST-1B@srcf.ucam.org
> > >http://www.srcf.ucam.org/mailman/listinfo/cst-1b
> >
> >
> >
> _________________________________________________________________________
> > William R Sowerbutts (BtG)
> will@sowerbutts.com
> > Coder / Guru / Nrrrd
> http://sowerbutts.com
> >        main(){char*s=">#=0> ^#X@#@^7=";int c=0,m;for(;c<15;c++)for
> >          (m=-1;m<7;putchar(m++/6&c%3/2?10:s[c]-31&1<<m?42:32));}
> >
> >
>
>
> _______________________________________________
> CST-1B mailing list
> CST-1B@srcf.ucam.org
> http://www.srcf.ucam.org/mailman/listinfo/cst-1b
>