From: Rob McCool <robm@netscape.com>
Newsgroups: netscape.devs-nsapi
Subject: Re: semaphores and criticals
Date: Fri, 26 Jul 1996 19:28:17 -0700

RP Johns wrote:
> 
> NT3.51
> FasdtTrack 2.0
> NSAPI
> 
> I've got a message queue onto which multiple threads
> can put, and multiple threads can get. I need to make
> it thread safe.
> 
> It seems like semaphores and CRITICALS
> are the 2 choices at hand. Could someone point me or provide
> a few examples using sem_init, sem_grab, sem_release or
> crit_init, crit_enter, crit_exit. Given the above problem, not
> sure which is the best choice.
> 
> I've implemented something using the sem_* stuff but not
> sure I'm using it properly. Here's all the doc I've found:

The somewhat misnamed semaphore stuff is intended to provide server-wide
locking. Under NT, I would definitely use critical sections.

To use them, simply place calls to crit_enter and crit_exit around the
code that manipulates the queue. You should initialize a critical
section when you initialize the queue using crit_init(), e.g.

static CRITICAL qcrit;
[...]

int myinit(pblock *args, Session *unused, Request *unused2)
{
[...]
  qcrit = crit_init();
}

int mycode(pblock *pb, Session *sn, Request *rq)
{
  crit_enter(qcrit);
  /* manipulate the queue */
  crit_exit(qcrit);
}
--
Rob McCool, robm@netscape.com http://home.netscape.com/people/robm/
Stunt Programmer, Netscape Communications Corporation
It was working ten minutes ago, I swear...

Reproduced by permission of the author.