[boost] Re: Threads: monitors vs. primitives

From: jsiek_at_[hidden]
Date: 2000-08-14 21:03:14

William Kempf writes:
 > This supposes that there's ever a reason to have a Mutex instead of a 
 > MutexWithCV.  I'm not sure that the plain Mutex concept is ever 
 > really valid.  I realize that this is a shakey argument on my part, 
 > so maybe I should abandon it.  I guess I just don't feel good doing 
 > that just yet.  The nesting appeals to me, and I guess it will 
 > continue to until you can point out why it's appropriate for lock but 
 > not for condition.  Or, put in another way, why would we ever have a 
 > concrete mutex type with out an associated concrete condition type?

To explain why we need plain Mutex a a concept I'll take a little step
back...  The purpose of a concept is to describe the requirements
placed on a template argument by a template function or class. Now a
template function or class is more reusable the more abstract, or the
fewer the requirements on the template arguments. I call this the
"requirement minimization principal". Anotherwords, a template
function should always pick the minimal concept that "covers" the
function's requirements. Now it is easy to think of situations where a
particular template function would need a Mutex and not a
ConditionVariable, say to protect access to a global variable.  For
this template function we need a concept to describe the
requirements. The right choice is Mutex and not MutexWithCV because of
the minimization principal.

I have a slightly longer discussion of concept design, and
concept checking in a paper I just submitted for the NetObjectDays
template workshop:

http://www.lsc.nd.edu/~jsiek/concept_checking.pdf

Cheers,
Jeremy

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 Jeremy Siek                        www: http://www.lsc.nd.edu/~jsiek/
 Ph.D. Candidate                  email: jsiek_at_[hidden]
 Univ. of Notre Dame         cell phone: [phone]   
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