libvmon: track active threads count per process

This introduces vmon_proc_t.n_current_threads, a counter
reflecting the currently non-stale number of threads in an
is_threaded process.

You could get this by walking the threads linked list and
filtering out the is_stale entries, but in preparation of showing
this count in the charts hierarchy I'm caching the incrementally
maintained count so the list doesn't need to be walked
repeatedly.

Note it's important to suppress the is_stale nodes from the
count, so the count isn't being decremented when stale nodes get
finally removed from the list - instead when nodes transition to
being stale.  The count shown in charts should reflect the number
of thread rows seen at the same time (when --no-threads isn't in
use)

1 files changed, 7 insertions, 1 deletions

diff --git a/src/libvmon/vmon.c b/src/libvmon/vmon.c
index e8a8d23..b4c008c 100644
--- a/src/libvmon/vmon.c
+++ b/src/libvmon/vmon.c
@@ -442,6 +442,7 @@ static vmon_proc_t * proc_monitor(vmon_t *vmon, vmon_proc_t *parent, int pid, vm
 			list_add_tail(&proc->threads, &parent->threads);
 			parent->threads_changed = 1;
 			parent->is_threaded = 1;
+			parent->n_current_threads++;
 		} else {
 			list_add_tail(&proc->siblings, &parent->children);
 			parent->children_changed = 1;
@@ -643,6 +644,8 @@ static int proc_follow_threads(vmon_t *vmon, vmon_proc_t *proc, vmon_proc_follow
 		list_for_each_entry(tmp, &proc->threads, threads)
 			tmp->is_stale = 1;
 
+		proc->n_current_threads = 0;
+
 		/* FIXME: the changes count seems to be unused here, so this currently always returns SAMPLE_UNCHANGED, and
 		 * it's unclear to me if that was intentional or just never finished.
 		 */
@@ -679,8 +682,11 @@ static int proc_follow_threads(vmon_t *vmon, vmon_proc_t *proc, vmon_proc_follow
 
 	list_for_each_entry_safe(tmp, _tmp, &proc->threads, threads) {
 		/* set children not found to stale status so the caller can respond and on our next sample invocation we will unmonitor them */
-		if (tmp->generation != vmon->generation)
+		if (tmp->generation != vmon->generation) {
 			tmp->is_stale = 1;
+			assert(proc->n_current_threads);
+			proc->n_current_threads--;
+		}
 	}
 
 	return changes ? SAMPLE_CHANGED : SAMPLE_UNCHANGED;