Fix semaphore destruction (bug 12674).

This commit fixes semaphore destruction by either using 64b atomic
operations (where available), or by using two separate fields when only
32b atomic operations are available.  In the latter case, we keep a
conservative estimate of whether there are any waiting threads in one
bit of the field that counts the number of available tokens, thus
allowing sem_post to atomically both add a token and determine whether
it needs to call futex_wake.

See:
https://sourceware.org/ml/libc-alpha/2014-12/msg00155.html

1 files changed, 14 insertions, 4 deletions

diff --git a/nptl/tst-sem13.c b/nptl/tst-sem13.c
index 068d79e85e..1560e91443 100644
--- a/nptl/tst-sem13.c
+++ b/nptl/tst-sem13.c
@@ -33,9 +33,14 @@ do_test (void)
       perror ("sem_timedwait did not fail with EINVAL");
       return 1;
     }
-  if (u.ns.nwaiters != 0)
+#if __HAVE_64B_ATOMICS
+  unsigned int nwaiters = (u.ns.data >> SEM_NWAITERS_SHIFT);
+#else
+  unsigned int nwaiters = u.ns.nwaiters;
+#endif
+  if (nwaiters != 0)
     {
-      printf ("sem_timedwait modified nwaiters: %ld\n", u.ns.nwaiters);
+      printf ("sem_timedwait modified nwaiters: %d\n", nwaiters);
       return 1;
     }
 
@@ -52,9 +57,14 @@ do_test (void)
       perror ("2nd sem_timedwait did not fail with ETIMEDOUT");
       return 1;
     }
-  if (u.ns.nwaiters != 0)
+#if __HAVE_64B_ATOMICS
+  nwaiters = (u.ns.data >> SEM_NWAITERS_SHIFT);
+#else
+  nwaiters = u.ns.nwaiters;
+#endif
+  if (nwaiters != 0)
     {
-      printf ("2nd sem_timedwait modified nwaiters: %ld\n", u.ns.nwaiters);
+      printf ("2nd sem_timedwait modified nwaiters: %d\n", nwaiters);
       return 1;
     }