Re: [boost] What's a Mutex ? (Was: Re: Threads)

From: Valentin Bonnard (Bonnard.V_at_[hidden])
Date: 2000-08-06 13:56:30

Lois Goldthwaite wrote:
> 
> Valentin Bonnard wrote:
> 
> > Most Mutex seem to be about lock (aka enter)/unlock (aka leave),
> > but some are about P/V.

> Quote from Practical Unix Programming by Robbins and Robbins:
> 
> "In 1965, E. W. Dijkstra proposed the semaphore abstraction for high-level
> management of mutual exclusion and synchronization. A semaphore is an integer
> variable with two atomic operations: 'wait' and 'signal.' Other names for
> 'wait' are 'down,' 'P,' and 'lock.' Other names for 'signal' are 'up,' 'V,'
> 'unlock,' and 'post.' "

I also wrote:

VB> - the Java class jsync.Mutex: an exclusive lock, only one thread 
VB>   can enter the critical section

or, to quote the doc for fsync.Mutex:

   Class for providing mutual exclusion of threads. Only one thread can
   enter critical section guarded by mutex (but can do it several
times).

So fsync.Mutex is just something that can be locked and unlocked, 
not something with P/V operations.

I have read many descriptions of mutex classes, and most of them are 
vague and incomplete. Some are even misleading.

> It's my understanding that 'P' and 'V' stand for some words in Dutch, but I
> don't know what they are.

I was wondering was they could mean (esp. since Post = V, not P).

-- 
Valentin Bonnard