doc/examples: add synchronize_rcu()

[urcu.git] / doc / examples / urcu-flavors / qsbr.c

diff --git a/doc/examples/urcu-flavors/qsbr.c b/doc/examples/urcu-flavors/qsbr.c
index 75302f0d31cf035afe2036039210fc3cb90fdf71..1dbd54635cbe06a4ca71bb9a60fdb87bcb8c9dec 100644 (file)
--- 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