MEDIUM: counters: add sc1_trackers/sc2_trackers

Returns the current amount of concurrent connections tracking the same
tracked counters. This number is automatically incremented when tracking
begins and decremented when tracking stops. It differs from sc1_conn_cur in
that it does not rely on any stored information but on the table's reference
count (the "use" value which is returned by "show table" on the CLI). This
may sometimes be more suited for layer7 tracking.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index bfd9729..8128c53 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -8276,6 +8276,15 @@
   connection could result in many backend sessions if some HTTP keep-alive is
   performed over the connection with the client. See also src_sess_rate.
 
+sc1_trackers
+sc2_trackers
+  Returns the current amount of concurrent connections tracking the same
+  tracked counters. This number is automatically incremented when tracking
+  begins and decremented when tracking stops. It differs from sc1_conn_cur in
+  that it does not rely on any stored information but on the table's reference
+  count (the "use" value which is returned by "show table" on the CLI). This
+  may sometimes be more suited for layer7 tracking.
+
 so_id <integer>
   Applies to the socket's id. Useful in frontends with many bind keywords.
 
diff --git a/src/session.c b/src/session.c
index 0bee957..a4c53a1 100644
--- a/src/session.c
+++ b/src/session.c
@@ -3597,6 +3597,28 @@
 	return acl_fetch_bytes_out_rate(&px->table, smp, stktable_lookup_key(&px->table, key));
 }
 
+/* set temp integer to the number of active trackers on the SC1 entry */
+static int
+acl_fetch_sc1_trackers(struct proxy *px, struct session *l4, void *l7, unsigned int opt,
+                       const struct arg *args, struct sample *smp)
+{
+	if (!l4->stkctr1_entry)
+		return 0;
+
+	return l4->stkctr1_entry->ref_cnt;
+}
+
+/* set temp integer to the number of active trackers on the SC1 entry */
+static int
+acl_fetch_sc2_trackers(struct proxy *px, struct session *l4, void *l7, unsigned int opt,
+                       const struct arg *args, struct sample *smp)
+{
+	if (!l4->stkctr2_entry)
+		return 0;
+
+	return l4->stkctr2_entry->ref_cnt;
+}
+
 /* set temp integer to the number of used entries in the table pointed to by expr.
  * Accepts exactly 1 argument of type table.
  */
@@ -3644,6 +3666,7 @@
 	{ "sc1_kbytes_out",     acl_parse_int,   acl_fetch_sc1_kbytes_out,     acl_match_int, ACL_USE_TCP4_VOLATILE, 0 },
 	{ "sc1_sess_cnt",       acl_parse_int,   acl_fetch_sc1_sess_cnt,       acl_match_int, ACL_USE_NOTHING,       0 },
 	{ "sc1_sess_rate",      acl_parse_int,   acl_fetch_sc1_sess_rate,      acl_match_int, ACL_USE_NOTHING,       0 },
+	{ "sc1_trackers",       acl_parse_int,   acl_fetch_sc1_trackers,       acl_match_int, ACL_USE_NOTHING,       0 },
 	{ "sc2_bytes_in_rate",  acl_parse_int,   acl_fetch_sc2_bytes_in_rate,  acl_match_int, ACL_USE_NOTHING,       0 },
 	{ "sc2_bytes_out_rate", acl_parse_int,   acl_fetch_sc2_bytes_out_rate, acl_match_int, ACL_USE_NOTHING,       0 },
 	{ "sc2_clr_gpc0",       acl_parse_int,   acl_fetch_sc2_clr_gpc0,       acl_match_int, ACL_USE_NOTHING,       0 },
@@ -3660,6 +3683,7 @@
 	{ "sc2_kbytes_out",     acl_parse_int,   acl_fetch_sc2_kbytes_out,     acl_match_int, ACL_USE_TCP4_VOLATILE, 0 },
 	{ "sc2_sess_cnt",       acl_parse_int,   acl_fetch_sc2_sess_cnt,       acl_match_int, ACL_USE_NOTHING,       0 },
 	{ "sc2_sess_rate",      acl_parse_int,   acl_fetch_sc2_sess_rate,      acl_match_int, ACL_USE_NOTHING,       0 },
+	{ "sc2_trackers",       acl_parse_int,   acl_fetch_sc2_trackers,       acl_match_int, ACL_USE_NOTHING,       0 },
 	{ "src_bytes_in_rate",  acl_parse_int,   acl_fetch_src_bytes_in_rate,  acl_match_int, ACL_USE_TCP4_VOLATILE, ARG1(1,TAB) },
 	{ "src_bytes_out_rate", acl_parse_int,   acl_fetch_src_bytes_out_rate, acl_match_int, ACL_USE_TCP4_VOLATILE, ARG1(1,TAB) },
 	{ "src_clr_gpc0",       acl_parse_int,   acl_fetch_src_clr_gpc0,       acl_match_int, ACL_USE_TCP4_VOLATILE, ARG1(1,TAB) },