1 files changed, 89 insertions, 0 deletions
diff --git a/nptl/sysdeps/generic/lowlevellock.h b/nptl/sysdeps/generic/lowlevellock.h
new file mode 100644
index 0000000000..9cffca83e6
--- /dev/null
+++ b/nptl/sysdeps/generic/lowlevellock.h
@@ -0,0 +1,89 @@
+/* Copyright (C) 2002 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   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, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+#include <atomic.h>
+
+
+/* Implement generic mutex.  Basic futex syscall support is required:
+
+     lll_futex_wait(futex, value) - call sys_futex with FUTEX_WAIT
+				    and third parameter VALUE
+
+     lll_futex_wake(futex, value) - call sys_futex with FUTEX_WAKE
+				    and third parameter VALUE
+*/
+
+
+/* Mutex lock counter:
+   bit 31 clear means unlocked;
+   bit 31 set means locked.
+
+   All code that looks at bit 31 first increases the 'number of
+   interested threads' usage counter, which is in bits 0-30.
+
+   All negative mutex values indicate that the mutex is still locked.  */
+
+
+static inline void
+__generic_mutex_lock (int *mutex)
+{
+  unsigned int v;
+
+  /* Bit 31 was clear, we got the mutex.  (this is the fastpath).  */
+  if (atomic_bit_test_set (mutex, 31) == 0)
+    return;
+
+  atomic_increment (mutex);
+
+  while (1)
+    {
+      if (atomic_bit_test_set (mutex, 31) == 0)
+	{
+	  atomic_decrement (mutex);
+	  return;
+	}
+
+      /* We have to wait now. First make sure the futex value we are
+	 monitoring is truly negative (i.e. locked). */
+      v = *mutex;
+      if (v >= 0)
+	continue;
+
+      lll_futex_wait (mutex, v);
+    }
+}
+
+
+static inline void
+__generic_mutex_unlock (int *mutex)
+{
+  /* Adding 0x80000000 to the counter results in 0 if and only if
+     there are not other interested threads - we can return (this is
+     the fastpath).  */
+  if (atomic_add_zero (0x80000000, mutex))
+    return;
+
+  /* There are other threads waiting for this mutex, wake one of them
+     up.  */
+  lll_futex_wake (mutex, 1);
+}
+
+
+#define lll_mutex_lock(futex) __generic_mutex_lock (&(futex))
+#define lll_mutex_unlock(futex) __generic_mutex_unlock (&(futex))