Re: Threads: better condition variables?

From: William Kempf (sirwillard_at_[hidden])
Date: 2000-08-10 17:11:12

--- In boost_at_[hidden], jsiek_at_l... wrote:
> scleary_at_j... writes:
>  > > As for the predicate to remove the while...  I considered that 
a lot 
>  > > yesterday while thinking on this subject.  The only problem I 
see is 
>  > > that you don't always have a predicate or while loop.
>  > 
>  > Right!  Condition variables can also be used on their own.  I've 
used them
>  > in that way before.  The example given by Jeremy was using CV's 
as a
> 
> I'm not familiar with the usage scenario you're alluding to
> here. Could you give an example?

To implement a gate.  If the gate is closed you wait on the 
condition, but once the condition is signaled there isn't really a 
reason to retest to see if the gate is opened.  This is just one 
simple example.

>  > monitor, not as CV's in their own right.  I'd recommend leaving 
pthread CV's
>  > largely as-is, but adding a Monitor class that wraps the while 
Predicate
>  > loop.
> 
> I'm not sure I like the use of the word "monitor" in this sense. 
I've
> always thought that a monitor is a class that automatically 
serializes
> accesses to its member functions. I know that signal() and wait() 
were
> discussed in Hoare's paper, but I thought he was using "condition
> variable" for that part of the functionality.

Yes, Hoare used a CV.  In this sense a monitor is really just a 
programming idiom.  However, a monitor can be a first class object as 
well.  Some are proposing that this is the only synchronization type 
that we need.