1 files changed, 103 insertions, 0 deletions
diff --git a/nptl/sem_post.c b/nptl/sem_post.c
new file mode 100644
index 0000000000..06d835907e
--- /dev/null
+++ b/nptl/sem_post.c
@@ -0,0 +1,103 @@
+/* sem_post -- post to a POSIX semaphore.  Generic futex-using version.
+   Copyright (C) 2003-2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Jakub Jelinek <jakub@redhat.com>, 2003.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <atomic.h>
+#include <errno.h>
+#include <sysdep.h>
+#include <lowlevellock.h>	/* lll_futex* used by the old code.  */
+#include <futex-internal.h>
+#include <internaltypes.h>
+#include <semaphore.h>
+
+#include <shlib-compat.h>
+
+
+/* See sem_wait for an explanation of the algorithm.  */
+int
+__new_sem_post (sem_t *sem)
+{
+  struct new_sem *isem = (struct new_sem *) sem;
+  int private = isem->private;
+
+#if __HAVE_64B_ATOMICS
+  /* Add a token to the semaphore.  We use release MO to make sure that a
+     thread acquiring this token synchronizes with us and other threads that
+     added tokens before (the release sequence includes atomic RMW operations
+     by other threads).  */
+  /* TODO Use atomic_fetch_add to make it scale better than a CAS loop?  */
+  uint64_t d = atomic_load_relaxed (&isem->data);
+  do
+    {
+      if ((d & SEM_VALUE_MASK) == SEM_VALUE_MAX)
+	{
+	  __set_errno (EOVERFLOW);
+	  return -1;
+	}
+    }
+  while (!atomic_compare_exchange_weak_release (&isem->data, &d, d + 1));
+
+  /* If there is any potentially blocked waiter, wake one of them.  */
+  if ((d >> SEM_NWAITERS_SHIFT) > 0)
+    futex_wake (((unsigned int *) &isem->data) + SEM_VALUE_OFFSET, 1, private);
+#else
+  /* Add a token to the semaphore.  Similar to 64b version.  */
+  unsigned int v = atomic_load_relaxed (&isem->value);
+  do
+    {
+      if ((v >> SEM_VALUE_SHIFT) == SEM_VALUE_MAX)
+	{
+	  __set_errno (EOVERFLOW);
+	  return -1;
+	}
+    }
+  while (!atomic_compare_exchange_weak_release
+	 (&isem->value, &v, v + (1 << SEM_VALUE_SHIFT)));
+
+  /* If there is any potentially blocked waiter, wake one of them.  */
+  if ((v & SEM_NWAITERS_MASK) != 0)
+    futex_wake (&isem->value, 1, private);
+#endif
+
+  return 0;
+}
+versioned_symbol (libpthread, __new_sem_post, sem_post, GLIBC_2_1);
+
+
+#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
+int
+attribute_compat_text_section
+__old_sem_post (sem_t *sem)
+{
+  int *futex = (int *) sem;
+
+  /* We must need to synchronize with consumers of this token, so the atomic
+     increment must have release MO semantics.  */
+  atomic_write_barrier ();
+  (void) atomic_increment_val (futex);
+  /* We always have to assume it is a shared semaphore.  */
+  int err = lll_futex_wake (futex, 1, LLL_SHARED);
+  if (__builtin_expect (err, 0) < 0)
+    {
+      __set_errno (-err);
+      return -1;
+    }
+  return 0;
+}
+compat_symbol (libpthread, __old_sem_post, sem_post, GLIBC_2_0);
+#endif