X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=urcu.h;h=c77b26f958e34b8521f1b8363d83b6492cb46b0f;hb=9d335088c7c7eb6219e32ec9426d336f3a211a77;hp=d417f34b52ddd1ce1509835dd0b7f062436d96f2;hpb=27b012e271a82b9a0d94543688904f207cd154ea;p=urcu.git

diff --git a/urcu.h b/urcu.h
index d417f34..c77b26f 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")
 
@@ -9,20 +25,89 @@
 #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"
-		     : "+m" (v->counter));
+		     : "+m" (*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
 
+#ifdef DEBUG_YIELD
+#include <sched.h>
+
+#define YIELD_READ 	(1 << 0)
+#define YIELD_WRITE	(1 << 1)
+
+extern unsigned int yield_active;
+extern unsigned int __thread rand_yield;
+
+static inline void debug_yield_read(void)
+{
+	if (yield_active & YIELD_READ)
+		if (rand_r(&rand_yield) & 0x1)
+			sched_yield();
+}
+
+static inline void debug_yield_write(void)
+{
+	if (yield_active & YIELD_WRITE)
+		if (rand_r(&rand_yield) & 0x1)
+			sched_yield();
+}
+
+static inline void debug_yield_init(void)
+{
+	rand_yield = time(NULL) ^ pthread_self();
+}
+#else
+static inline void debug_yield_read(void)
+{
+}
+
+static inline void debug_yield_write(void)
+{
+}
+
+static inline void debug_yield_init(void)
+{
+
+}
+#endif
+
 /* Global quiescent period parity */
 extern int urcu_qparity;
 
@@ -34,28 +119,34 @@ static inline int get_urcu_qparity(void)
 }
 
 /*
- * returns urcu_parity.
+ * urcu_parity should be declared on the caller's stack.
  */
-static inline int rcu_read_lock(void)
+static inline void rcu_read_lock(int *urcu_parity)
 {
-	int urcu_parity = get_urcu_qparity();
-	urcu_active_readers[urcu_parity]++;
+	debug_yield_read();
+	*urcu_parity = get_urcu_qparity();
+	debug_yield_read();
+	urcu_active_readers[*urcu_parity]++;
+	debug_yield_read();
 	/*
 	 * Increment active readers count before accessing the pointer.
 	 * See force_mb_all_threads().
 	 */
 	barrier();
-	return urcu_parity;
+	debug_yield_read();
 }
 
-static inline void rcu_read_unlock(int urcu_parity)
+static inline void rcu_read_unlock(int *urcu_parity)
 {
+	debug_yield_read();
 	barrier();
+	debug_yield_read();
 	/*
 	 * Finish using rcu before decrementing the pointer.
 	 * See force_mb_all_threads().
 	 */
-	urcu_active_readers[urcu_parity]--;
+	urcu_active_readers[*urcu_parity]--;
+	debug_yield_read();
 }
 
 extern void *urcu_publish_content(void **ptr, void *new);
@@ -64,6 +155,6 @@ 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 */