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, 35 insertions, 66 deletions

diff --git a/nptl/sem_wait.c b/nptl/sem_wait.c
index df11933..c1fd10c 100644
--- a/nptl/sem_wait.c
+++ b/nptl/sem_wait.c
@@ -17,80 +17,18 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
-#include <sysdep.h>
-#include <lowlevellock.h>
-#include <internaltypes.h>
-#include <semaphore.h>
-
-#include <pthreadP.h>
-#include <shlib-compat.h>
-#include <atomic.h>
-
-
-void
-attribute_hidden
-__sem_wait_cleanup (void *arg)
-{
-  struct new_sem *isem = (struct new_sem *) arg;
-
-  atomic_decrement (&isem->nwaiters);
-}
-
-/* This is in a seperate function in order to make sure gcc
-   puts the call site into an exception region, and thus the
-   cleanups get properly run.  */
-static int
-__attribute__ ((noinline))
-do_futex_wait (struct new_sem *isem)
-{
-  int err, oldtype = __pthread_enable_asynccancel ();
-
-  err = lll_futex_wait (&isem->value, 0, isem->private ^ FUTEX_PRIVATE_FLAG);
-
-  __pthread_disable_asynccancel (oldtype);
-  return err;
-}
+#include "sem_waitcommon.c"
 
 int
 __new_sem_wait (sem_t *sem)
 {
-  struct new_sem *isem = (struct new_sem *) sem;
-  int err;
-
-  if (atomic_decrement_if_positive (&isem->value) > 0)
+  if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
     return 0;
-
-  atomic_increment (&isem->nwaiters);
-
-  pthread_cleanup_push (__sem_wait_cleanup, isem);
-
-  while (1)
-    {
-      err = do_futex_wait(isem);
-      if (err != 0 && err != -EWOULDBLOCK)
-	{
-	  __set_errno (-err);
-	  err = -1;
-	  break;
-	}
-
-      if (atomic_decrement_if_positive (&isem->value) > 0)
-	{
-	  err = 0;
-	  break;
-	}
-    }
-
-  pthread_cleanup_pop (0);
-
-  atomic_decrement (&isem->nwaiters);
-
-  return err;
+  else
+    return __new_sem_wait_slow((struct new_sem *) sem, NULL);
 }
 versioned_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
 
-
 #if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
 int
 attribute_compat_text_section
@@ -121,3 +59,34 @@ __old_sem_wait (sem_t *sem)
 
 compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
 #endif
+
+int
+__new_sem_trywait (sem_t *sem)
+{
+  /* We must not fail spuriously, so require a definitive result even if this
+     may lead to a long execution time.  */
+  if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
+    return 0;
+  __set_errno (EAGAIN);
+  return -1;
+}
+versioned_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
+#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
+int
+__old_sem_trywait (sem_t *sem)
+{
+  int *futex = (int *) sem;
+  int val;
+
+  if (*futex > 0)
+    {
+      val = atomic_decrement_if_positive (futex);
+      if (val > 0)
+	return 0;
+    }
+
+  __set_errno (EAGAIN);
+  return -1;
+}
+compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
+#endif