Fix: relayd: missing session unlock on error path

[lttng-tools.git] / src / bin / lttng-relayd / viewer-session.h

diff --git a/src/bin/lttng-relayd/viewer-session.h b/src/bin/lttng-relayd/viewer-session.h
index ebde2dd1dbfc77cfb08c541f898ed89f76253138..f70daed7ba5940617c6a834864575e92d1f54822 100644 (file)
--- a/src/bin/lttng-relayd/viewer-session.h
+++ b/src/bin/lttng-relayd/viewer-session.h
@@ -20,6 +20,7 @@
 #include <common/trace-chunk.h>
 
 #include "session.h"
+#include "lttng-viewer-abi.h"
 
 struct relay_viewer_session {
        /*
@@ -30,7 +31,33 @@ struct relay_viewer_session {
         */
        struct cds_list_head session_list;      /* RCU list. */
        pthread_mutex_t session_list_lock;      /* Protects list updates. */
-       /* Once set, the current trace chunk of a viewer must not change. */
+       /*
+        * The viewer session's current trace chunk is initially set, when
+        * a viewer attaches to the viewer session, to a copy the corresponding
+        * relay_session's current trace chunk.
+        *
+        * A live session always attempts to "catch-up" to the newest available
+        * trace chunk. This means that when a viewer reaches the end of a
+        * trace chunk, the viewer session may not transition to the "next" one:
+        * it jumps to the most recent trace chunk available (the one being
+        * produced by the relay_session). Hence, if the producer performs
+        * multiple rotations before a viewer completes the consumption of a
+        * trace chunk, it will skip over those "intermediary" trace chunks.
+        *
+        * A viewer session updates its current trace chunk when:
+        *   1) new viewer streams are created,
+        *   2) a new index is requested,
+        *   3) metadata is requested.
+        *
+        * Hence, as a general principle, the viewer session will reference the
+        * most recent trace chunk available _even if its streams do not point to
+        * it_. It indicates which trace chunk viewer streams should transition
+        * to when the end of their current trace chunk is reached.
+        *
+        * Note that a viewer session's trace chunk points to the session's
+        * output directory. The sub-directories in which the various stream files
+        * are created are considered as being a part of their name.
+        */
        struct lttng_trace_chunk *current_trace_chunk;
 };