Date: Tue, 20 Jan 2004 11:47:37 -0500 From: Craig Rodrigues <rodrigc@crodrigues.org> To: Daniel Eischen <eischen@vigrid.com> Cc: freebsd-threads@freebsd.org Subject: Re: sem_wait() is a cancellation point in libkse? Message-ID: <20040120164737.GA778@crodrigues.org> In-Reply-To: <Pine.GSO.4.10.10401200057220.14763-100000@pcnet5.pcnet.com> References: <20040120053945.GA4096@crodrigues.org> <Pine.GSO.4.10.10401200057220.14763-100000@pcnet5.pcnet.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Jan 20, 2004 at 01:02:12AM -0500, Daniel Eischen wrote:
> > is a _sem_wait() which looks like it is doing
> > cancellation stuff, but it doesn't
> > seem to be working.
> >
> libc uses strong symbols for sem_wait which override
> the weak symbols that libpthread is using. The sem_wait
> in libc isn't a cancellation point yet. I think the
> sem_foo stuff in libc should be refactored to just make
> the system calls (like semop/semctl) and not know about
> waiting threads. The threads libraries can wrap them
> if they want to provide cancellation points and faster
> userland thread switches for (process scope) thread
> waits/wakeups.
The thread libraries already seem to wrap sem_wait().
It is in:
src/lib/libc_r/uthread/uthread_sem.c
src/lib/libthr/thread/thr_sem.c
src/lib/libpthread/thread/thr_sem.c
sem_wait() in those files is implemented as _sem_wait(), and
is a proper cancellation point.
Is there anything wrong with making sem_wait() a weak symbol
in libc? I tried the following patch, and it works
quite nicely, i.e. tst-cancel12 in the NPTL tests now
succeeds.
--- sem.c.orig Tue Jan 20 11:37:35 2004
+++ sem.c Tue Jan 20 11:44:20 2004
@@ -53,6 +53,8 @@
static LIST_HEAD(, sem) named_sems = LIST_HEAD_INITIALIZER(&named_sems);
static pthread_mutex_t named_sems_mtx = PTHREAD_MUTEX_INITIALIZER;
+__weak_reference(_sem_wait, sem_wait);
+
static void
sem_free(sem_t sem)
{
@@ -255,7 +257,7 @@
}
int
-sem_wait(sem_t *sem)
+_sem_wait(sem_t *sem)
{
int retval;
--
Craig Rodrigues
http://crodrigues.org
rodrigc@crodrigues.org
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20040120164737.GA778>