From 4d1ce26fea0296ff67791c881836393fdd020cf9 Mon Sep 17 00:00:00 2001
From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Tue, 22 Sep 2009 19:01:10 -0400
Subject: [PATCH 1/1] add rcu_cmpxchg_pointer

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---
 urcu-qsbr-static.h | 16 ++++++++++++++++
 urcu-qsbr.c        |  6 ++++++
 urcu-qsbr.h        |  4 ++++
 urcu-static.h      | 16 ++++++++++++++++
 urcu.c             |  6 ++++++
 urcu.h             |  4 ++++
 6 files changed, 52 insertions(+)

diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h
index 22a93b2..c0467cd 100644
--- a/urcu-qsbr-static.h
+++ b/urcu-qsbr-static.h
@@ -244,6 +244,22 @@ static inline void _rcu_thread_online(void)
 		STORE_SHARED(p, v);			\
 	})
 
+/**
+ * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
+ * is as expected by "old". If succeeds, returns the previous pointer to the
+ * data structure, which can be safely freed after waiting for a quiescent state
+ * using synchronize_rcu(). If fails (unexpected value), returns old (which
+ * should not be freed !).
+ */
+
+#define _rcu_cmpxchg_pointer(p, old, _new)		\
+	({						\
+		if (!__builtin_constant_p(_new) ||	\
+		    ((_new) != NULL))			\
+			wmb();				\
+		cmpxchg(p, old, _new);			\
+	})
+
 /**
  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
  * pointer to the data structure, which can be safely freed after waiting for a
diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index f681c05..5c6eaa0 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -255,6 +255,12 @@ void *rcu_assign_pointer_sym(void **p, void *v)
 	return STORE_SHARED(p, v);
 }
 
+void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
+{
+	wmb();
+	return cmpxchg(p, old, _new);
+}
+
 void *rcu_xchg_pointer_sym(void **p, void *v)
 {
 	wmb();
diff --git a/urcu-qsbr.h b/urcu-qsbr.h
index 9a2c82f..346f906 100644
--- a/urcu-qsbr.h
+++ b/urcu-qsbr.h
@@ -103,6 +103,10 @@ extern void *rcu_assign_pointer_sym(void **p, void *v);
 #define rcu_assign_pointer(p, v)			\
 	rcu_assign_pointer_sym((void **)(p), (v))
 
+extern void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new);
+#define rcu_cmpxchg_pointer(p, old, _new)		\
+	rcu_cmpxchg_pointer_sym((void **)(p), (old), (_new))
+
 extern void *rcu_xchg_pointer_sym(void **p, void *v);
 #define rcu_xchg_pointer(p, v)				\
 	rcu_xchg_pointer_sym((void **)(p), (v))
diff --git a/urcu-static.h b/urcu-static.h
index 0c6891e..f819e6f 100644
--- a/urcu-static.h
+++ b/urcu-static.h
@@ -276,6 +276,22 @@ static inline void _rcu_read_unlock(void)
 		STORE_SHARED(p, v);			\
 	})
 
+/**
+ * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
+ * is as expected by "old". If succeeds, returns the previous pointer to the
+ * data structure, which can be safely freed after waiting for a quiescent state
+ * using synchronize_rcu(). If fails (unexpected value), returns old (which
+ * should not be freed !).
+ */
+
+#define _rcu_cmpxchg_pointer(p, old, _new)		\
+	({						\
+		if (!__builtin_constant_p(_new) ||	\
+		    ((_new) != NULL))			\
+			wmb();				\
+		cmpxchg(p, old, _new);			\
+	})
+
 /**
  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
  * pointer to the data structure, which can be safely freed after waiting for a
diff --git a/urcu.c b/urcu.c
index d474fc8..a8f85c6 100644
--- a/urcu.c
+++ b/urcu.c
@@ -347,6 +347,12 @@ void *rcu_xchg_pointer_sym(void **p, void *v)
 	return xchg(p, v);
 }
 
+void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
+{
+	wmb();
+	return cmpxchg(p, old, _new);
+}
+
 void *rcu_publish_content_sym(void **p, void *v)
 {
 	void *oldptr;
diff --git a/urcu.h b/urcu.h
index af7d75c..5d92aa7 100644
--- a/urcu.h
+++ b/urcu.h
@@ -75,6 +75,10 @@ extern void *rcu_assign_pointer_sym(void **p, void *v);
 #define rcu_assign_pointer(p, v)			\
 	rcu_assign_pointer_sym((void **)(p), (v))
 
+extern void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new);
+#define rcu_cmpxchg_pointer(p, old, _new)		\
+	rcu_cmpxchg_pointer_sym((void **)(p), (old), (_new))
+
 extern void *rcu_xchg_pointer_sym(void **p, void *v);
 #define rcu_xchg_pointer(p, v)				\
 	rcu_xchg_pointer_sym((void **)(p), (v))
-- 
2.34.1