Public headers: use SPDX identifiers

[urcu.git] / include / urcu / static / pointer.h

diff --git a/include/urcu/static/pointer.h b/include/urcu/static/pointer.h
index 891daed2994ba8a58c0b7f1bdfe10d886d37f91c..055a9b884524581a58610a7f9f40dbe0df780a76 100644 (file)
--- a/include/urcu/static/pointer.h
+++ b/include/urcu/static/pointer.h
@@ -1,31 +1,17 @@
+// SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+// SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
+//
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
 #ifndef _URCU_POINTER_STATIC_H
 #define _URCU_POINTER_STATIC_H
 
 /*
- * urcu/static/pointer.h
- *
  * Userspace RCU header. Operations on pointers.
  *
  * TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
  * RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
  *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
- *
- * This 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.
- *
- * This 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 this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  */
 
@@ -61,6 +47,10 @@ extern "C" {
  * optimizations are taken care of by the "memory_order_consume" atomic
  * load.
  *
+ * Use the gcc __atomic_load() rather than C11/C++11 atomic load
+ * explicit because the pointer used as input argument is a pointer,
+ * not an _Atomic type as required by C11/C++11.
+ *
  * By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of
  * volatile access to implement rcu_dereference rather than
  * memory_order_consume load from the C11/C++11 standards.
@@ -80,33 +70,34 @@ extern "C" {
  * expanded directly in non-LGPL code.
  */
 
-#ifdef URCU_DEREFERENCE_USE_VOLATILE
-# define __rcu_dereference(p)  CMM_LOAD_SHARED(p)
-#else
-# if defined (__cplusplus)
-#  if __cplusplus >= 201103L
-#   include <atomic>
-#   define __rcu_dereference(p)        ((std::atomic<__typeof__(p)>)(p)).load(std::memory_order_consume)
-#  else
-#   define __rcu_dereference(p)        CMM_LOAD_SHARED(x)
-#  endif
-# else
-#  if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L)
-#   include <stdatomic.h>
-#   define __rcu_dereference(p)        atomic_load_explicit(&(p), memory_order_consume)
-#  else
-#   define __rcu_dereference(p)        CMM_LOAD_SHARED(p)
-#  endif
-# endif
+#if !defined (URCU_DEREFERENCE_USE_VOLATILE) &&                \
+       ((defined (__cplusplus) && __cplusplus >= 201103L) ||   \
+       (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L))
+# define __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
 #endif
 
-#define _rcu_dereference(p)                                            \
-                               __extension__                           \
-                               ({                                      \
-                               __typeof__(p) _________p1 = __rcu_dereference(p); \
-                               cmm_smp_read_barrier_depends();         \
-                               (_________p1);                          \
-                               })
+/*
+ * If p is const (the pointer itself, not what it points to), using
+ * __typeof__(p) would declare a const variable, leading to
+ * -Wincompatible-pointer-types errors.  Using the statement expression
+ * makes it an rvalue and gets rid of the const-ness.
+ */
+#ifdef __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
+# define _rcu_dereference(p) __extension__ ({                                          \
+                               __typeof__(__extension__ ({                             \
+                                       __typeof__(p) __attribute__((unused)) _________p0 = { 0 }; \
+                                       _________p0;                                    \
+                               })) _________p1;                                        \
+                               __atomic_load(&(p), &_________p1, __ATOMIC_CONSUME);    \
+                               (_________p1);                                          \
+                       })
+#else
+# define _rcu_dereference(p) __extension__ ({                                          \
+                               __typeof__(p) _________p1 = CMM_LOAD_SHARED(p);         \
+                               cmm_smp_read_barrier_depends();                         \
+                               (_________p1);                                          \
+                       })
+#endif
 
 /**
  * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer