Add comments for the relayd ctrl socket mutex

[lttng-tools.git] / src / common / consumer.h

diff --git a/src/common/consumer.h b/src/common/consumer.h
index 8bcf27d2c99166393cfa035ed644b4cd267e60df..8e7cec9944e88381a28fca8984ea0e3ac64c487b 100644 (file)
--- a/src/common/consumer.h
+++ b/src/common/consumer.h
@@ -138,9 +138,22 @@ struct consumer_relayd_sock_pair {
        int net_seq_idx;
        /* Number of stream associated with this relayd */
        unsigned int refcount;
+       /*
+        * Mutex protecting the control socket to avoid out of order packets
+        * between threads sending data to the relayd. Since metadata data is sent
+        * over that socket, at least two sendmsg() are needed (header + data)
+        * creating a race for packets to overlap between threads using it.
+        */
        pthread_mutex_t ctrl_sock_mutex;
-       /* Sockets information */
+
+       /* Control socket. Command and metadata are passed over it */
        struct lttcomm_sock control_sock;
+
+       /*
+        * We don't need a mutex at this point since we only splice or write single
+        * large chunk of data with a header appended at the begining. Moreover,
+        * this socket is for now only used in a single thread.
+        */
        struct lttcomm_sock data_sock;
        struct lttng_ht_node_ulong node;
 };