Re: [boost] Re: Threads by Jeremy and Monitors in one?

From: jpanzer_at_[hidden]
Date: 2000-08-09 20:54:17

Thomas Holenstein wrote:

>  > Ok, to help people get a feel for what we want, I've written up a
>  > strawman concept description for Mutex and ReentrantMutex.
>  >
>  > http://www.lsc.nd.edu/~jsiek/Mutex.html
>
> Ok.  When I could extend the class lock with notify() and wait(), I
> can get something very much like a monitor with IMHO minimal effort.
> I'll show you what I mean at the classical buffer: (This is mostly
> stolen from Greg)
>
> public class SharedBuffer {
>   int p, c, full;
>   vector buf;
> public
>   buffer(int n) : p(0), c(0), full(0), buf(n) {}
>
>   void send(int m) {
>     X::lock l(*this);
>     if (full == buf.size()) l.wait();
>     buf[p] = m;
>     p = (p+1)%buf.size();
>     ++full;
>     if (full == 1) l.notify();
>   }
>
>   int receive() {
>     X::lock l(*this);
>     if (full == 0) l.wait();
>     int i = buf[c];
>     c = (c + 1)%buf.size();
>     --full;
>     if (full == buf.size()-1) l.notify();
>     return i;
>   }
> };
>
> I like this idea, to be honest.  It's just a very bit different than
> Jeremys, but I think it adds much flexibility.

I like this (X should be SharedBuffer above, right? In which
case SharedBuffer has to either inherit from something or
provide the required nested typedefs, etc. itself.)

I think that the wait/notify would be something applied to
the resource, not the lock object.

There are two things required of SharedBuffer above,
mutual exclusion and notification.  I think these
should be separable for efficiency (sometimes you want
mutual exclusion but don't need notification, and
notification may require additional data for X.)  Should
this be a separate concept like "Waitable"?

>
> This way, you can get practical the same interface as with a monitor,
> (but effectively, you are more flexible, as you don't need to lock
> complete procedures)
>
> If some people want a timeout, I'd suggest throwing an exception after
> a specified time.

I think this would be a perfect place to use exceptions.

John Panzer