relayd: clarify viewer_get_next_index no rotation condition

The condition identifying cases where a viewer_get_next_index must not
perform a viewer stream rotation is relatively tricky to comprehend.

Split it in two intermediate variables, and use those variables to
print debugging statements when conditions for not performing a
rotation match.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ieca2fbf879c8ed45c0b3aa6035ac32679b12dcdc

diff --git a/src/bin/lttng-relayd/live.cpp b/src/bin/lttng-relayd/live.cpp
index 9cdc1c8d751d78b0876d1cd35c88026b72b4c6cf..96ec11efcde387e67e8884b63593f705933effb4 100644 (file)
--- a/src/bin/lttng-relayd/live.cpp
+++ b/src/bin/lttng-relayd/live.cpp
@@ -29,6 +29,7 @@
 #include <urcu/futex.h>
 #include <urcu/rculist.h>
 #include <urcu/uatomic.h>
+#include <string>
 
 #include <common/common.h>
 #include <common/compat/endian.h>
@@ -1602,6 +1603,9 @@ int viewer_get_next_index(struct relay_connection *conn)
        struct relay_stream *rstream = NULL;
        struct ctf_trace *ctf_trace = NULL;
        struct relay_viewer_stream *metadata_viewer_stream = NULL;
+       bool viewer_stream_and_session_in_same_chunk, viewer_stream_one_rotation_behind;
+       uint64_t stream_file_chunk_id = -1ULL, viewer_session_chunk_id = -1ULL;
+       enum lttng_trace_chunk_status status;
 
        LTTNG_ASSERT(conn);
 
@@ -1682,12 +1686,50 @@ int viewer_get_next_index(struct relay_connection *conn)
         * This allows clients to consume all the packets of a trace chunk
         * after a session's destruction.
         */
-       if (!lttng_trace_chunk_ids_equal(conn->viewer_session->current_trace_chunk, vstream->stream_file.trace_chunk) &&
-                       !(rstream->completed_rotation_count == vstream->last_seen_rotation_count + 1 && !rstream->trace_chunk)) {
-               DBG("Viewer session and viewer stream chunk IDs differ: "
-                               "vsession chunk %p vstream chunk %p",
+       if (vstream->stream_file.trace_chunk) {
+               status = lttng_trace_chunk_get_id(
+                               vstream->stream_file.trace_chunk,
+                               &stream_file_chunk_id);
+               LTTNG_ASSERT(status == LTTNG_TRACE_CHUNK_STATUS_OK);
+       }
+       if (conn->viewer_session->current_trace_chunk) {
+               status = lttng_trace_chunk_get_id(
                                conn->viewer_session->current_trace_chunk,
-                               vstream->stream_file.trace_chunk);
+                               &viewer_session_chunk_id);
+               LTTNG_ASSERT(status == LTTNG_TRACE_CHUNK_STATUS_OK);
+       }
+
+       viewer_stream_and_session_in_same_chunk = lttng_trace_chunk_ids_equal(
+                       conn->viewer_session->current_trace_chunk,
+                       vstream->stream_file.trace_chunk);
+       viewer_stream_one_rotation_behind = rstream->completed_rotation_count ==
+                       vstream->last_seen_rotation_count + 1;
+
+       if (viewer_stream_and_session_in_same_chunk) {
+               DBG("Transition to latest chunk check (%s -> %s): Same chunk, no need to rotate",
+                               vstream->stream_file.trace_chunk ?
+                                               std::to_string(stream_file_chunk_id).c_str() :
+                                               "None",
+                               conn->viewer_session->current_trace_chunk ?
+                                               std::to_string(viewer_session_chunk_id).c_str() :
+                                               "None");
+       } else if (viewer_stream_one_rotation_behind && !rstream->trace_chunk) {
+               DBG("Transition to latest chunk check (%s -> %s): One chunk behind relay stream which is being destroyed, no need to rotate",
+                               vstream->stream_file.trace_chunk ?
+                                               std::to_string(stream_file_chunk_id).c_str() :
+                                               "None",
+                               conn->viewer_session->current_trace_chunk ?
+                                               std::to_string(viewer_session_chunk_id).c_str() :
+                                               "None");
+       } else {
+               DBG("Transition to latest chunk check (%s -> %s): Viewer stream chunk ID and viewer session chunk ID differ, rotating viewer stream",
+                               vstream->stream_file.trace_chunk ?
+                                               std::to_string(stream_file_chunk_id).c_str() :
+                                               "None",
+                               conn->viewer_session->current_trace_chunk ?
+                                               std::to_string(viewer_session_chunk_id).c_str() :
+                                               "None");
+
                viewer_stream_rotate_to_trace_chunk(vstream,
                                conn->viewer_session->current_trace_chunk);
                vstream->last_seen_rotation_count =
@@ -1732,7 +1774,6 @@ int viewer_get_next_index(struct relay_connection *conn)
         */
        if (!vstream->stream_file.handle) {
                char file_path[LTTNG_PATH_MAX];
-               enum lttng_trace_chunk_status status;
                struct fs_handle *fs_handle;
 
                ret = utils_stream_file_path(rstream->path_name,