[lttng-dev] [PATCH lttng-tools] Atomically update relayd stream and session id

[David Goulet]

Improve protection to the variables where the uatomic_add_return() call
does a volatile access and returns the value atomically incremented.

Enclose that in two new functions, one for each id, which helps with the
code semantic and brings a single call site for the value update making
the code easier to scale and understand when adding contention to those
variables.

Signed-off-by: David Goulet <dgoulet at efficios.com>
---
 src/bin/lttng-relayd/lttng-relayd.h |   19 +++++++++++++++++++
 src/bin/lttng-relayd/main.c         |    9 +++++----
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/src/bin/lttng-relayd/lttng-relayd.h b/src/bin/lttng-relayd/lttng-relayd.h
index edd32d6..b2566a1 100644
--- a/src/bin/lttng-relayd/lttng-relayd.h
+++ b/src/bin/lttng-relayd/lttng-relayd.h
@@ -23,6 +23,9 @@
 #include <urcu.h>
 #include <urcu/wfqueue.h>
 
+extern uint64_t relayd_last_stream_id;
+extern uint64_t relayd_last_session_id;
+
 /*
  * Queue used to enqueue relay requests
  */
@@ -81,4 +84,20 @@ struct relay_command {
 	unsigned int version_check_done:1;
 };
 
+/*
+ * Atomically increment the id and return the next stream id.
+ */
+static inline uint64_t relayd_get_next_stream_id(void)
+{
+	return (uint64_t) uatomic_add_return(&relayd_last_stream_id, 1);
+}
+
+/*
+ * Atomically increment the id and return the next session id.
+ */
+static inline uint64_t relayd_get_next_session_id(void)
+{
+	return (uint64_t) uatomic_add_return(&relayd_last_session_id, 1);
+}
+
 #endif /* LTTNG_RELAYD_H */
diff --git a/src/bin/lttng-relayd/main.c b/src/bin/lttng-relayd/main.c
index 6627310..a042ce6 100644
--- a/src/bin/lttng-relayd/main.c
+++ b/src/bin/lttng-relayd/main.c
@@ -82,8 +82,9 @@ static pthread_t listener_thread;
 static pthread_t dispatcher_thread;
 static pthread_t worker_thread;
 
-static uint64_t last_relay_stream_id;
-static uint64_t last_relay_session_id;
+/* Declared extern in lttng-relayd.h */
+uint64_t relayd_last_stream_id;
+uint64_t relayd_last_session_id;
 
 /*
  * Relay command queue.
@@ -968,7 +969,7 @@ int relay_create_session(struct lttcomm_relayd_hdr *recv_hdr,
 		goto error;
 	}
 
-	session->id = ++last_relay_session_id;
+	session->id = relayd_get_next_session_id();
 	session->sock = cmd->sock;
 	cmd->session = session;
 
@@ -1032,7 +1033,7 @@ int relay_add_stream(struct lttcomm_relayd_hdr *recv_hdr,
 	}
 
 	rcu_read_lock();
-	stream->stream_handle = ++last_relay_stream_id;
+	stream->stream_handle = relayd_get_next_stream_id();
 	stream->prev_seq = -1ULL;
 	stream->session = session;
 
-- 
1.7.10.4