htl: Add pshared semaphore support

The implementation is extremely similar to the nptl implementation, but
with slight differences in the futex interface. This fixes some of BZ
25521.

1 files changed, 55 insertions, 0 deletions

diff --git a/sysdeps/htl/sem-waitfast.c b/sysdeps/htl/sem-waitfast.c
new file mode 100644
index 0000000000..7ece73da26
--- /dev/null
+++ b/sysdeps/htl/sem-waitfast.c
@@ -0,0 +1,55 @@
+/* Lock a semaphore if it does not require blocking.  Generic version.
+   Copyright (C) 2005-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <semaphore.h>
+#include <errno.h>
+
+#include <pt-internal.h>
+
+int
+__sem_waitfast (struct new_sem *isem, int definitive_result)
+{
+#if __HAVE_64B_ATOMICS
+  uint64_t d = atomic_load_relaxed (&isem->data);
+
+  do
+    {
+      if ((d & SEM_VALUE_MASK) == 0)
+	break;
+      if (atomic_compare_exchange_weak_acquire (&isem->data, &d, d - 1))
+	/* Successful down.  */
+	return 0;
+    }
+  while (definitive_result);
+  return -1;
+#else
+  unsigned v = atomic_load_relaxed (&isem->value);
+
+  do
+    {
+      if ((v >> SEM_VALUE_SHIFT) == 0)
+	break;
+      if (atomic_compare_exchange_weak_acquire (&isem->value,
+	    &v, v - (1 << SEM_VALUE_SHIFT)))
+	/* Successful down.  */
+	return 0;
+    }
+  while (definitive_result);
+  return -1;
+#endif
+}