X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=doc%2Fexamples%2Furcu-flavors%2Fqsbr.c;h=1dbd54635cbe06a4ca71bb9a60fdb87bcb8c9dec;hb=d7818a6fd0c57b576f3bacc67ddd62bc8a78fb05;hp=75302f0d31cf035afe2036039210fc3cb90fdf71;hpb=7ff54418ffac313216eac70d7af1474a78c21706;p=urcu.git

diff --git a/doc/examples/urcu-flavors/qsbr.c b/doc/examples/urcu-flavors/qsbr.c
index 75302f0..1dbd546 100644
--- a/doc/examples/urcu-flavors/qsbr.c
+++ b/doc/examples/urcu-flavors/qsbr.c
@@ -98,6 +98,12 @@ int main(int argc, char **argv)
 	 */
 	cds_list_for_each_entry_safe(node, n, &mylist, node) {
 		cds_list_del_rcu(&node->node);
+		/*
+		 * call_rcu() will ensure that the handler
+		 * "rcu_free_node" is executed after a grace period.
+		 * call_rcu() can be called from RCU read-side critical
+		 * sections.
+		 */
 		call_rcu(&node->rcu_head, rcu_free_node);
 	}
 
@@ -120,6 +126,16 @@ int main(int argc, char **argv)
 
 	rcu_thread_online();
 
+	/*
+	 * We can also wait for a quiescent state by calling
+	 * synchronize_rcu() rather than using call_rcu(). It is usually
+	 * a slower approach than call_rcu(), because the latter can
+	 * batch work. Moreover, call_rcu() can be called from a RCU
+	 * read-side critical section, but synchronize_rcu() ensures the
+	 * caller thread is offline, thus acting as a quiescent state.
+	 */
+	synchronize_rcu();
+
 	/*
 	 * Waiting for previously called call_rcu handlers to complete
 	 * before program exits, or in library destructors, is a good