X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.h;h=bee7715270794c3e83cede4acb1741a98d361ac6;hp=363021d7832927e288705e42f7c31f4d36486d72;hb=b1b5ce8f610ee61647b10d93d7a61b5fbf1f2ccd;hpb=f69f195a06af55b7501ed2f59ed719970727ce5b

diff --git a/urcu.h b/urcu.h
index 363021d..bee7715 100644
--- a/urcu.h
+++ b/urcu.h
@@ -21,6 +21,36 @@ static inline void atomic_inc(int *v)
 /* Nop everywhere except on alpha. */
 #define smp_read_barrier_depends()
 
+/*
+ * Prevent the compiler from merging or refetching accesses.  The compiler
+ * is also forbidden from reordering successive instances of ACCESS_ONCE(),
+ * but only when the compiler is aware of some particular ordering.  One way
+ * to make the compiler aware of ordering is to put the two invocations of
+ * ACCESS_ONCE() in different C statements.
+ *
+ * This macro does absolutely -nothing- to prevent the CPU from reordering,
+ * merging, or refetching absolutely anything at any time.  Its main intended
+ * use is to mediate communication between process-level code and irq/NMI
+ * handlers, all running on the same CPU.
+ */
+#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
+
+/**
+ * rcu_dereference - fetch an RCU-protected pointer in an
+ * RCU read-side critical section.  This pointer may later
+ * be safely dereferenced.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (currently only the Alpha), and, more importantly, documents
+ * exactly which pointers are protected by RCU.
+ */
+
+#define rcu_dereference(p)     ({ \
+				typeof(p) _________p1 = ACCESS_ONCE(p); \
+				smp_read_barrier_depends(); \
+				(_________p1); \
+				})
+
 #define SIGURCU SIGUSR1
 
 /* Global quiescent period parity */
@@ -58,6 +88,9 @@ static inline void rcu_read_unlock(int urcu_parity)
 	urcu_active_readers[urcu_parity]--;
 }
 
+extern void rcu_write_lock(void);
+extern void rcu_write_unlock(void);
+
 extern void *urcu_publish_content(void **ptr, void *new);
 
 /*