From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Date: Mon, 9 Feb 2009 05:54:50 +0000 (-0500)
Subject: Use xchg in publish content
X-Git-Tag: v0.1~312
X-Git-Url: https://git.lttng.org/?p=urcu.git;a=commitdiff_plain;h=f4a486ac095bd844d0c18995737d589b8f085b69

Use xchg in publish content

Also changes the publish content parameter. Now takes the pointer itself as
first parameter rather than a pointer to the pointer.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
---

diff --git a/test_urcu.c b/test_urcu.c
index 39408a0..b92a7d7 100644
--- a/test_urcu.c
+++ b/test_urcu.c
@@ -127,7 +127,7 @@ void *thr_writer(void *arg)
 		if (old)
 			assert(old->a == 8);
 		new->a = 8;
-		old = urcu_publish_content((void **)&test_rcu_pointer, new);
+		old = urcu_publish_content(&test_rcu_pointer, new);
 		rcu_copy_mutex_unlock();
 		/* can be done after unlock */
 		if (old)
diff --git a/test_urcu_timing.c b/test_urcu_timing.c
index 9903705..f97a5c1 100644
--- a/test_urcu_timing.c
+++ b/test_urcu_timing.c
@@ -145,7 +145,7 @@ void *thr_writer(void *arg)
 			assert(old->a == 8);
 		}
 		new->a = 8;
-		old = urcu_publish_content((void **)&test_rcu_pointer, new);
+		old = urcu_publish_content(&test_rcu_pointer, new);
 		rcu_copy_mutex_unlock();
 		/* can be done after unlock */
 		if (old) {
diff --git a/urcu.c b/urcu.c
index 23a985b..9fde623 100644
--- a/urcu.c
+++ b/urcu.c
@@ -151,42 +151,6 @@ void synchronize_rcu(void)
 	debug_yield_write();
 }
 
-/*
- * Return old pointer, OK to free, no more reference exist.
- * Called under rcu_write_lock.
- */
-void *urcu_publish_content(void **ptr, void *new)
-{
-	void *oldptr;
-
-	debug_yield_write();
-	internal_urcu_lock();
-	debug_yield_write();
-	/*
-	 * We can publish the new pointer before we change the current qparity.
-	 * Readers seeing the new pointer while being in the previous qparity
-	 * window will make us wait until the end of the quiescent state before
-	 * we release the unrelated memory area. However, given we hold the
-	 * urcu_mutex, we are making sure that no further garbage collection can
-	 * occur until we release the mutex, therefore we guarantee that this
-	 * given reader will have completed its execution using the new pointer
-	 * when the next quiescent state window will be over.
-	 */
-	oldptr = *ptr;
-	debug_yield_write();
-	rcu_assign_pointer(*ptr, new);
-
-	debug_yield_write();
-	switch_qparity();
-	debug_yield_write();
-	switch_qparity();
-	debug_yield_write();
-	internal_urcu_unlock();
-	debug_yield_write();
-
-	return oldptr;
-}
-
 void urcu_add_reader(pthread_t id)
 {
 	struct reader_data *oldarray;
diff --git a/urcu.h b/urcu.h
index 27695d4..fb8cedf 100644
--- a/urcu.h
+++ b/urcu.h
@@ -33,6 +33,45 @@ static inline void atomic_inc(int *v)
 		     : "+m" (*v));
 }
 
+#define xchg(ptr, v)							\
+	((__typeof__(*(ptr)))__xchg((unsigned long)(v), (ptr), sizeof(*(ptr))))
+
+struct __xchg_dummy {
+	unsigned long a[100];
+};
+#define __xg(x) ((struct __xchg_dummy *)(x))
+
+/*
+ * Note: no "lock" prefix even on SMP: xchg always implies lock anyway
+ * Note 2: xchg has side effect, so that attribute volatile is necessary,
+ *	  but generally the primitive is invalid, *ptr is output argument. --ANK
+ */
+static inline unsigned long __xchg(unsigned long x, volatile void *ptr,
+				   int size)
+{
+	switch (size) {
+	case 1:
+		asm volatile("xchgb %b0,%1"
+			     : "=q" (x)
+			     : "m" (*__xg(ptr)), "0" (x)
+			     : "memory");
+		break;
+	case 2:
+		asm volatile("xchgw %w0,%1"
+			     : "=r" (x)
+			     : "m" (*__xg(ptr)), "0" (x)
+			     : "memory");
+		break;
+	case 4:
+		asm volatile("xchgl %0,%1"
+			     : "=r" (x)
+			     : "m" (*__xg(ptr)), "0" (x)
+			     : "memory");
+		break;
+	}
+	return x;
+}
+
 /* Nop everywhere except on alpha. */
 #define smp_read_barrier_depends()
 
@@ -190,9 +229,29 @@ static inline void rcu_read_unlock(void)
 		(p) = (v); \
 	})
 
-extern void *urcu_publish_content(void **ptr, void *new);
+#define rcu_xchg_pointer(p, v) \
+	({ \
+		if (!__builtin_constant_p(v) || \
+		    ((v) != NULL)) \
+			wmb(); \
+		xchg(p, v); \
+	})
+
 extern void synchronize_rcu(void);
 
+/*
+ * Exchanges the pointer and waits for quiescent state.
+ * The pointer returned can be freed.
+ */
+#define urcu_publish_content(p, v) \
+	({ \
+		void *oldptr; \
+		debug_yield_write(); \
+		oldptr = rcu_xchg_pointer(p, v); \
+		synchronize_rcu(); \
+		oldptr; \
+	})
+
 /*
  * Reader thread registration.
  */