add rcu_cmpxchg_pointer

[urcu.git] / urcu-static.h

diff --git a/urcu-static.h b/urcu-static.h
index 91d37470fe785ffffd13dc7ebbebeb1357170cd7..f819e6fc9aa07e9f4e58329661bf5a494936bb25 100644 (file)
--- a/urcu-static.h
+++ b/urcu-static.h
@@ -81,7 +81,9 @@
  * data read before the pointer read by speculating the value of the pointer.
  * Correct ordering is ensured because the pointer is read as a volatile access.
  * This acts as a global side-effect operation, which forbids reordering of
- * dependent memory operations.
+ * dependent memory operations. Note that such concern about dependency-breaking
+ * optimizations will eventually be taken care of by the "memory_order_consume"
+ * addition to forthcoming C++ standard.
  *
  * Should match rcu_assign_pointer() or rcu_xchg_pointer().
  */
@@ -115,6 +117,12 @@
  */
 #define KICK_READER_LOOPS 10000
 
+#ifdef DEBUG_RCU
+#define rcu_assert(args...)    assert(args)
+#else
+#define rcu_assert(args...)
+#endif
+
 #ifdef DEBUG_YIELD
 #include <sched.h>
 #include <time.h>
@@ -125,10 +133,10 @@
 #define YIELD_WRITE    (1 << 1)
 
 /*
- * Updates without CONFIG_URCU_AVOID_SIGNALS are much slower. Account this in
+ * Updates without URCU_MB are much slower. Account this in
  * the delay.
  */
-#ifdef CONFIG_URCU_AVOID_SIGNALS
+#ifdef URCU_MB
 /* maximum sleep delay, in us */
 #define MAX_SLEEP 50
 #else
@@ -171,7 +179,7 @@ static inline void debug_yield_init(void)
 }
 #endif
 
-#ifdef CONFIG_URCU_AVOID_SIGNALS
+#ifdef URCU_MB
 static inline void reader_barrier()
 {
        smp_mb();
@@ -268,6 +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