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

From: Thomas Holenstein (tholenst_at_[hidden])
Date: 2000-08-09 17:25:13

 > 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.

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.

For wait and notify I would use a queue, as I always missed this in
Java.  

There are some detail questions open:  What happens with multiple
notifys, which thread enters first, the waiting or the locked, but I
think these are detail.

Thomas