Date: Thu, 19 Nov 2009 12:02:30 -0500 From: John Baldwin <jhb@freebsd.org> To: Daniel Eischen <deischen@freebsd.org> Cc: threads@freebsd.org Subject: Re: Using pthread_once() in libc Message-ID: <200911191202.30738.jhb@freebsd.org> In-Reply-To: <Pine.GSO.4.64.0911191143300.8401@sea.ntplx.net> References: <200911191030.14151.jhb@freebsd.org> <Pine.GSO.4.64.0911191143300.8401@sea.ntplx.net>
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On Thursday 19 November 2009 11:48:54 am Daniel Eischen wrote:
> On Thu, 19 Nov 2009, John Baldwin wrote:
>
> > I would like to provide a pthread_once()-like facility in libc that library
> > bits can use to initialize data safely rather than trying to home-roll their
> > own variants (see the recent commit to stdtime in libc). Ideally what I
> > would like to do is have libc use the "real" pthread_once() when libthr is
> > linked in and fall back to a simple stub without libthr linked in. I know we
> > already do something like this for _spinlock() and friends. My question is
> > what is the most correct way to do this? Should libc grow a new _once()
> > symbol ala _spinlock() that is a weak symbol to a stub version and
> > pthread_once() in thr_once.c would override that, or should there be a
> > _pthread_once() in libc that is a stub in place of the current stub_zero? I
> > noticed a comment in thr_spinlock.c saying the spinlock stuff is kept for
> > backwards compat. Does this mean that for the future we would like to expose
> > pthread symbols directly in libc? Meaning would we rather have libc export a
> > pthread_once() and that ideally libc would be using pthread_mutex_lock/unlock
> > instead of _spinlock/unlock?
>
> pthread_once() is already a stub in libc that gets overloaded with the
> real thing when libthr is linked. See libc/gen/_pthread_stubs.c.
> Isn't that what you want or does it not serve your purpose?
Hmm, the libc stub will never run the init routine. I would like to do
something like this:
Index: stdtime/localtime.c
===================================================================
--- stdtime/localtime.c (revision 199529)
+++ stdtime/localtime.c (working copy)
@@ -235,9 +235,8 @@
static char lcl_TZname[TZ_STRLEN_MAX + 1];
static int lcl_is_set;
-static int gmt_is_set;
+static pthread_once_t gmt_once = PTHREAD_ONCE_INIT;
static pthread_rwlock_t lcl_rwlock = PTHREAD_RWLOCK_INITIALIZER;
-static pthread_mutex_t gmt_mutex = PTHREAD_MUTEX_INITIALIZER;
char * tzname[2] = {
wildabbr,
@@ -1464,6 +1463,17 @@
return tmp;
}
+static void
+gmt_init(void)
+{
+
+#ifdef ALL_STATE
+ gmtptr = (struct state *) malloc(sizeof *gmtptr);
+ if (gmtptr != NULL)
+#endif /* defined ALL_STATE */
+ gmtload(gmtptr);
+}
+
/*
** gmtsub is to gmtime as localsub is to localtime.
*/
@@ -1476,16 +1486,7 @@
{
register struct tm * result;
- _MUTEX_LOCK(&gmt_mutex);
- if (!gmt_is_set) {
-#ifdef ALL_STATE
- gmtptr = (struct state *) malloc(sizeof *gmtptr);
- if (gmtptr != NULL)
-#endif /* defined ALL_STATE */
- gmtload(gmtptr);
- gmt_is_set = TRUE;
- }
- _MUTEX_UNLOCK(&gmt_mutex);
+ _pthread_once(&gmt_once, gmt_init);
result = timesub(timep, offset, gmtptr, tmp);
#ifdef TM_ZONE
/*
--
John Baldwin
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