charts: assert that descendents of stale are stale

This is really how things are implemented today, which may
actually be incorrect in some edge case scenarios... but let's
assert it holds true currently to aid debugging some spurious
asserts in vcr_shift_below_row_up_one() about row vs.
hierarchy_end.

The potential issue I see with this assumption as-is is it's
entirely possible to have descendants survive a parent's demise,
grandchildren don't have to exit when a parent does.  But it
might be OK to treat it that way, as they'll be rediscovered as
children of PID 1, and there's no strict need to preserve
continuity of their associated charts state across that
transition.  It's rare enough that I don't think it's worth
worrying about, but maybe this is what's happening with the
asserts during startup specifically; when things are daemonizing
/ double forking etc.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/charts.c b/src/charts.c
index 0e000df..34caf58 100644
--- a/src/charts.c
+++ b/src/charts.c
@@ -844,10 +844,10 @@ static void draw_chart_rest(vwm_charts_t *charts, vwm_chart_t *chart, vmon_proc_
 		 * a repeated pass within the same sample - we can't realize these effects twice.
 		 */
 		if (sample_duration_idx == 0) { /* some things need to only be done once per sample duration, some at the start, some at the end */
+			static int	in_stale = 0;
 
 			if (proc->is_stale) { /* we "realize" stale processes only in the first draw within a sample duration */
 				/* what to do when a process (subtree) has gone away */
-				static int	in_stale = 0;
 				int		in_stale_entrypoint = 0;
 
 				/* I snowflake the stale processes from the leaves up for a more intuitive snowflake order...
@@ -857,6 +857,12 @@ static void draw_chart_rest(vwm_charts_t *charts, vwm_chart_t *chart, vmon_proc_
 				if (!in_stale) {
 					VWM_TRACE("entered stale at chart=%p depth=%i row=%i", chart, *depth, *row);
 					in_stale_entrypoint = in_stale = 1;
+
+					/* this advances row to the last row of all descendants, the minus one is needed since we're
+					 * already at proc's row, and count_rows() includes it in the count.  Imagine there are no
+					 * descendants, count_rows returns 1, we turn that into 0, and (*row) stays unchanged, which
+					 * is correct - we snowflake ourself and that's that.
+					 */
 					(*row) += count_rows(proc) - 1;
 				}
 
@@ -897,8 +903,14 @@ static void draw_chart_rest(vwm_charts_t *charts, vwm_chart_t *chart, vmon_proc_
 				}
 
 				return;
+			} else {
+				/* If we're not stale, assert we're not in_stale, because the count_rows() used above is indiscriminate.
+				 * if there's !is_stale descendents then we'll get confused as-is.
+				 */
+				assert(!in_stale);
 			}
 
+
 			/* use the generation number to avoid recomputing this stuff for callbacks recurring on the same process in the same sample */
 			if (proc_ctxt->generation != charts->vmon.generation) {
 				proc_ctxt->stime_delta = proc_stat->stime - proc_ctxt->last_stime;