X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.h;h=9431da547bfcc8245d07969de426ac33c7fe3d2d;hp=363021d7832927e288705e42f7c31f4d36486d72;hb=cdcb92bbb9e54201e0982844e3ca9cb4fd9b31e5;hpb=f69f195a06af55b7501ed2f59ed719970727ce5b

diff --git a/urcu.h b/urcu.h
index 363021d..9431da5 100644
--- a/urcu.h
+++ b/urcu.h
@@ -1,6 +1,22 @@
 #ifndef _URCU_H
 #define _URCU_H
 
+/*
+ * urcu.h
+ *
+ * Userspace RCU header
+ *
+ * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ *
+ * Credits for Paul e. McKenney <paulmck@linux.vnet.ibm.com>
+ * for inspiration coming from the Linux kernel RCU and rcu-preempt.
+ *
+ * The barrier, mb, rmb, wmb, atomic_inc, smp_read_barrier_depends, ACCESS_ONCE
+ * and rcu_dereference primitives come from the Linux kernel.
+ *
+ * Distributed under GPLv2
+ */
+
 /* The "volatile" is due to gcc bugs */
 #define barrier() __asm__ __volatile__("": : :"memory")
 
@@ -9,9 +25,6 @@
 #define rmb()   asm volatile("lfence":::"memory")
 #define wmb()   asm volatile("sfence" ::: "memory")
 
-
-
-/* x86 32 */
 static inline void atomic_inc(int *v)
 {
 	asm volatile("lock; incl %0"
@@ -21,6 +34,36 @@ 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 */
@@ -58,12 +101,15 @@ 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);
 
 /*
  * Reader thread registration.
  */
 extern void urcu_register_thread(void);
-extern void urcu_register_thread(void);
+extern void urcu_unregister_thread(void);
 
 #endif /* _URCU_H */