X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=doc%2Fexamples%2Furcu-flavors%2Fqsbr.c;h=1dbd54635cbe06a4ca71bb9a60fdb87bcb8c9dec;hb=2fec8f05f010408e989356e6f9d8c1e191ba4dfa;hp=bb12f9f5772d60d282ab5d6272782c7a455c26ef;hpb=88c3c5ba50ae3d5a847b4214840234b8f116e928;p=urcu.git

diff --git a/doc/examples/urcu-flavors/qsbr.c b/doc/examples/urcu-flavors/qsbr.c
index bb12f9f..1dbd546 100644
--- a/doc/examples/urcu-flavors/qsbr.c
+++ b/doc/examples/urcu-flavors/qsbr.c
@@ -85,21 +85,12 @@ int main(int argc, char **argv)
 			goto end;
 	}
 
-	/*
-	 * For all RCU flavors except QSBR, we need to explicitly mark
-	 * RCU read-side critical sections with rcu_read_lock() and
-	 * rcu_read_unlock(). They can be nested. Those are no-ops for
-	 * the QSBR flavor.
-	 */
-	rcu_read_lock();
-
 	/*
 	 * RCU traversal of the linked list.
 	 */
 	cds_list_for_each_entry_rcu(node, &mylist, node) {
 		printf("Value: %" PRIu64 "\n", node->value);
 	}
-	rcu_read_unlock();
 
 	/*
 	 * Removing nodes from linked list. Safe against concurrent RCU
@@ -107,6 +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);
 	}
 
@@ -129,6 +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