urcu qsbr: add DEBUG_RCU self check

[urcu.git] / urcu-static.h

diff --git a/urcu-static.h b/urcu-static.h
index 1921097dbb8596a9d134fecdea5e2bcfe9444c2d..66a06df85e0f72080bdb79a991e0f5d3e8691125 100644 (file)
--- 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().
  */