On Wed, 10 May 2023 at 12:20, Jonathan Wakely via Libstdc++ < libstd...@gcc.gnu.org> wrote:
> This patch would avoid TSan false positives when using timed waiting > functions on mutexes and condvars, but as noted below, it changes the > semantics. > > I'm not sure whether we want this workaround in place until tsan gets > fixed. > > On one hand, there's no guarantee that those functions use the right > clock anyway (and they won't do unless a recent-ish glibc is used). But > on the other hand, if they normally would use the right clock because > you have glibc support, it's not ideal for tsan to cause a different > clock to be used. > But of course, it's not ideal to get false positives from tsan either (especially when it looks like a libstdc++ bug, as initially reported to me). > > -- >8 -- > > As noted in https://github.com/llvm/llvm-project/issues/62623 there are > no tsan interceptors for the new POSIX-1:202x APIs added by > https://austingroupbugs.net/view.php?id=1216 so tsan gives false > positive warnings. > > Disable the uses of the new APIs when tsan is active. This changes the > semantics of those functions, because it can change which clock is used > for the wait. This means those functions might be affected by system > clock adjustments when tsan is used, when they would not be affected > otherwise. > > libstdc++-v3/ChangeLog: > > * acinclude.m4 (GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT): Define > _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT to depend on _GLIBCXX_TSAN. > (GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK): Likewise for > _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK. > (GLIBCXX_CHECK_PTHREAD_RWLOCK_CLOCKLOCK): Likewise for > _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK. > * configure: Regenerate. > --- > libstdc++-v3/acinclude.m4 | 6 +++--- > libstdc++-v3/configure | 6 +++--- > 2 files changed, 6 insertions(+), 6 deletions(-) > > diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 > index 89e7f5f5f45..e2700b05ec3 100644 > --- a/libstdc++-v3/acinclude.m4 > +++ b/libstdc++-v3/acinclude.m4 > @@ -4284,7 +4284,7 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT], [ > [glibcxx_cv_PTHREAD_COND_CLOCKWAIT=no]) > ]) > if test $glibcxx_cv_PTHREAD_COND_CLOCKWAIT = yes; then > - AC_DEFINE(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT, 1, [Define if > pthread_cond_clockwait is available in <pthread.h>.]) > + AC_DEFINE(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT, (_GLIBCXX_TSAN==0), > [Define if pthread_cond_clockwait is available in <pthread.h>.]) > fi > > CXXFLAGS="$ac_save_CXXFLAGS" > @@ -4314,7 +4314,7 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK], [ > [glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK=no]) > ]) > if test $glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK = yes; then > - AC_DEFINE(_GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK, 1, [Define if > pthread_mutex_clocklock is available in <pthread.h>.]) > + AC_DEFINE(_GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK, (_GLIBCXX_TSAN==0), > [Define if pthread_mutex_clocklock is available in <pthread.h>.]) > fi > > CXXFLAGS="$ac_save_CXXFLAGS" > @@ -4346,7 +4346,7 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREAD_RWLOCK_CLOCKLOCK], [ > [glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK=no]) > ]) > if test $glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK = yes; then > - AC_DEFINE(_GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK, 1, [Define if > pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock are available in > <pthread.h>.]) > + AC_DEFINE(_GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK, (_GLIBCXX_TSAN==0), > [Define if pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock are > available in <pthread.h>.]) > fi > > CXXFLAGS="$ac_save_CXXFLAGS" > >
