From owner-freebsd-arch  Thu Oct 12 21:45: 3 2000
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Date: Thu, 12 Oct 2000 21:44:46 -0700
From: Jason Evans <jasone@canonware.com>
To: Terry Lambert <tlambert@primenet.com>
Cc: Alfred Perlstein <bright@wintelcom.net>,
	Chuck Paterson <cp@bsdi.com>, Mike Smith <msmith@FreeBSD.ORG>,
	arch@FreeBSD.ORG
Subject: Re: we need atomic_t
Message-ID: <20001012214446.H11949@canonware.com>
References: <20001012192229.F272@fw.wintelcom.net> <200010130251.TAA03945@usr05.primenet.com>
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In-Reply-To: <200010130251.TAA03945@usr05.primenet.com>; from tlambert@primenet.com on Fri, Oct 13, 2000 at 02:51:31AM +0000
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On Fri, Oct 13, 2000 at 02:51:31AM +0000, Terry Lambert wrote:
> > The reason for atomic_init/destroy is to intialize mutexes if they
> > are needed on the arch.  Basically atomic64_t on 32bit arches would
> > be a struct with a 64bit value and a mutex to protect it.
> 
> Tee hee hee.
> 
> How do I initialize the mutex that protects the mutex?
> 
> I think it's time to learn from the POSIX threads mutex
> implementation, wherein it is impossible to statically
> initialize a mutex, and to obtain that appearance, you
> have to trick the loader into doing the work using the
> section which is used for the construction of virtual
> base classes in C++ (see my modifications to the STL, as
> applied to the Moscow Center for Supercomuting Activites
> STL, which is the most up to date STL available).

Here's one of Butenhof's example programs, which uses POSIX threads:
-------------------------------------------------------------------------
/*
 * mutex_static.c
 *
 * Demonstrate static initialization of a mutex.
 */
#include <pthread.h>

/*
 * Declare a structure, with a mutex, statically initialized. This is the
 * same as using pthread_mutex_init, with the default attributes.
 */
typedef struct my_struct_tag {
    pthread_mutex_t     mutex;  /* Protects access to value */
    int                 value;  /* Access protected by mutex */
} my_struct_t;

my_struct_t data = {PTHREAD_MUTEX_INITIALIZER, 0};

int main (int argc, char *argv[])
{   
    return 0;
}
-------------------------------------------------------------------------

That looks like static mutex initialization to me. =)

Jason


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