Date: Thu, 19 Nov 2009 12:09:33 -0500 (EST) From: Daniel Eischen <deischen@freebsd.org> To: John Baldwin <jhb@freebsd.org> Cc: threads@freebsd.org Subject: Re: Using pthread_once() in libc Message-ID: <Pine.GSO.4.64.0911191204120.8401@sea.ntplx.net> In-Reply-To: <200911191202.30738.jhb@freebsd.org> References: <200911191030.14151.jhb@freebsd.org> <Pine.GSO.4.64.0911191143300.8401@sea.ntplx.net> <200911191202.30738.jhb@freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Thu, 19 Nov 2009, John Baldwin wrote: > 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: Well, I suppose you could do that. But what happens if libthr gets dlopen()'d and your once function needs to initialize a mutex or something that can only be properly done by a real threads library? Can we envision a scenario where that would be a problem? -- DE
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?Pine.GSO.4.64.0911191204120.8401>