X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-static.h;h=f819e6fc9aa07e9f4e58329661bf5a494936bb25;hp=1b3527fd2de649b087a502ec42af2098ba095ec3;hb=4d1ce26fea0296ff67791c881836393fdd020cf9;hpb=67ef1a2cd793e5dde7db32ef5210fc002c3325cd

diff --git a/urcu-static.h b/urcu-static.h
index 1b3527f..f819e6f 100644
--- a/urcu-static.h
+++ b/urcu-static.h
@@ -76,6 +76,15 @@
  * Inserts memory barriers on architectures that require them (currently only
  * Alpha) and documents which pointers are protected by RCU.
  *
+ * The compiler memory barrier in LOAD_SHARED() ensures that value-speculative
+ * optimizations (e.g. VSS: Value Speculation Scheduling) does not perform the
+ * 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. 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().
  */
 
@@ -108,6 +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>
@@ -117,8 +132,11 @@
 #define YIELD_READ 	(1 << 0)
 #define YIELD_WRITE	(1 << 1)
 
-/* Updates without DEBUG_FULL_MB are much slower. Account this in the delay */
-#ifdef DEBUG_FULL_MB
+/*
+ * Updates without URCU_MB are much slower. Account this in
+ * the delay.
+ */
+#ifdef URCU_MB
 /* maximum sleep delay, in us */
 #define MAX_SLEEP 50
 #else
@@ -161,7 +179,7 @@ static inline void debug_yield_init(void)
 }
 #endif
 
-#ifdef DEBUG_FULL_MB
+#ifdef URCU_MB
 static inline void reader_barrier()
 {
 	smp_mb();
@@ -258,6 +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