lib: introduce a read-write lock for northbound configurations

The upcoming gRPC-based northbound plugin will run on a separate
pthread, and it will need to have access to the running configuration
global variable.  Introduce a rw-lock to control concurrent access
to the running configuration. Add the lock inside the "nb_config"
structure so that it can be used to protect candidate configurations
as well (this might be necessary depending on the threading scheme
of future northbound plugins).

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

1 files changed, 6 insertions, 1 deletions

diff --git a/lib/libfrr.c b/lib/libfrr.c
index 0d4c8d6c0f..5970e70a6b 100644
--- a/lib/libfrr.c
+++ b/lib/libfrr.c
@@ -830,7 +830,12 @@ static int frr_config_read_in(struct thread *t)
 	/*
 	 * Update the shared candidate after reading the startup configuration.
 	 */
-	nb_config_replace(vty_shared_candidate_config, running_config, true);
+	pthread_rwlock_rdlock(&running_config->lock);
+	{
+		nb_config_replace(vty_shared_candidate_config, running_config,
+				  true);
+	}
+	pthread_rwlock_unlock(&running_config->lock);
 
 	return 0;
 }