From 8faea20349dc1d8cfd0117d28a3f1271083192d0 Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Tue, 6 May 2014 19:52:04 +0200
Subject: [PATCH 2/5] include: add lock-less reference counting primitives

* include/refcount.h: New file.
---
 include/refcount.h | 155 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 155 insertions(+)
 create mode 100644 include/refcount.h

diff --git a/include/refcount.h b/include/refcount.h
new file mode 100644
index 0000000..946938a
--- /dev/null
+++ b/include/refcount.h
@@ -0,0 +1,155 @@
+/* Lock-less reference counting primitives
+
+   Copyright (C) 2014 Free Software Foundation, Inc.
+
+   Written by Justus Winter <4winter@informatik.uni-hamburg.de>
+
+   This file is part of the GNU Hurd.
+
+   The GNU Hurd is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License as
+   published by the Free Software Foundation; either version 2, or (at
+   your option) any later version.
+
+   The GNU Hurd 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
+   General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with the GNU Hurd.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef _HURD_REFCOUNT_H_
+#define _HURD_REFCOUNT_H_
+
+#include <stdint.h>
+
+/* Simple reference counting.  */
+
+/* An opaque type.  You must not access these values directly.  */
+typedef uint32_t refcount_t;
+
+/* Initialize REF with REFERENCES.  */
+static inline void
+refcount_init (refcount_t *ref, uint32_t references)
+{
+  *ref = references;
+}
+
+/* Increment REF.  Return the result of the operation.  */
+static inline uint32_t
+refcount_ref (refcount_t *ref)
+{
+  return __atomic_add_fetch (ref, 1, __ATOMIC_RELAXED);
+}
+
+/* Decrement REF.  Return the result of the operation.  */
+static inline uint32_t
+refcount_deref (refcount_t *ref)
+{
+  return __atomic_sub_fetch (ref, 1, __ATOMIC_RELAXED);
+}
+
+/* Return REF.  */
+static inline uint32_t
+refcount_references (refcount_t *ref)
+{
+  return __atomic_load_n (ref, __ATOMIC_RELAXED);
+}
+
+/* Reference counting with weak references.  */
+
+/* An opaque type.  You must not access these values directly.  */
+typedef uint64_t refcounts_t;
+
+/* Instead, the functions manipulating refcounts_t values write the
+   results into this kind of objects.  */
+struct references {
+  uint32_t hard;
+  uint32_t weak;
+};
+
+union _references {
+  struct references refs;
+  refcounts_t rc;
+};
+
+/* Initialize REF with HARD and WEAK references.  */
+static inline void
+refcounts_init (refcounts_t *ref, uint32_t hard, uint32_t weak)
+{
+  ((union _references *) ref)->refs =
+    (struct references) { .hard = hard, .weak = weak };
+}
+
+/* Increment the hard reference count of REF.  If RESULT is not NULL,
+   the result of the operation is written there.  */
+static inline void
+refcounts_ref (refcounts_t *ref, struct references *result)
+{
+  const union _references op = { .refs = { .hard = 1 } };
+  refcounts_t r = __atomic_add_fetch (ref, op.rc, __ATOMIC_RELAXED);
+  if (result)
+    ((union _references *) result)->rc = r;
+}
+
+/* Decrement the hard reference count of REF.  If RESULT is not NULL,
+   the result of the operation is written there.  */
+static inline void
+refcounts_deref (refcounts_t *ref, struct references *result)
+{
+  const union _references op = { .refs = { .hard = 1 } };
+  refcounts_t r = __atomic_sub_fetch (ref, op.rc, __ATOMIC_RELAXED);
+  if (result)
+    ((union _references *) result)->rc = r;
+}
+
+/* Increment the weak reference count of REF.  If RESULT is not NULL,
+   the result of the operation is written there.  */
+static inline void
+refcounts_ref_weak (refcounts_t *ref, struct references *result)
+{
+  const union _references op = { .refs = { .weak = 1 } };
+  refcounts_t r = __atomic_add_fetch (ref, op.rc, __ATOMIC_RELAXED);
+  if (result)
+    ((union _references *) result)->rc = r;
+}
+
+/* Decrement the weak reference count of REF.  If RESULT is not NULL,
+   the result of the operation is written there.  */
+static inline void
+refcounts_deref_weak (refcounts_t *ref, struct references *result)
+{
+  const union _references op = { .refs = { .weak = 1 } };
+  refcounts_t r = __atomic_sub_fetch (ref, op.rc, __ATOMIC_RELAXED);
+  if (result)
+    ((union _references *) result)->rc = r;
+}
+
+/* Store the current reference counts of REF in RESULT.  */
+static inline void
+refcounts_references (refcounts_t *ref, struct references *result)
+{
+  ((union _references *) result)->rc =
+    __atomic_load_n (ref, __ATOMIC_RELAXED);
+}
+
+/* Return the hard reference count of REF.  */
+static inline uint32_t
+refcounts_hard_references (refcounts_t *ref)
+{
+  struct references result;
+  refcounts_references (ref, &result);
+  return result.hard;
+}
+
+/* Return the weak reference count of REF.  */
+static inline uint32_t
+refcounts_weak_references (refcounts_t *ref)
+{
+  struct references result;
+  refcounts_references (ref, &result);
+  return result.weak;
+}
+
+#endif /* _HURD_REFCOUNT_H_ */
-- 
2.0.0.rc0