[RFC] libstdc++: Do not use pthread_mutex_clocklock with ThreadSanitizer

[Jonathan Wakely <jwakely@redhat.com>]

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.

-- >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"