fsm: add osmo_fsm_inst_state_chg_keep_or_start_timer()
During FSM design for osmo-msc, I noticed that the current behavior that
keep_timer=true doesn't guarantee a running timer can make FSM design a bit
complex, especially when using osmo_tdef for timeout definitions.
A desirable keep_timer=true behavior is one that keeps the previous timer
running, but starts a timer if no timer is running yet.
The simplest example is: a given state repeatedly transitions back to itself,
but wants to set a timeout only on first entering, avoiding to restart the
timeout on re-entering.
Another example is a repeated transition between two or more states, where the
first time we enter this group a timeout should start, but it should not
restart from scratch on every transition.
When using osmo_tdef timeout definitions for this, so far separate meaningless
states have to be introduced that merely set a fixed timeout.
To simplify, add osmo_fsm_inst_state_chg_keep_or_start_timer(), and use this in
osmo_tdef_fsm_inst_state_chg() when both keep_timer == true *and* T != 0.
In tdef_test.ok, the changes show that on first entering state L, the previous
T=1 is now kept with a large remaining timeout. When entering state L from O,
where no timer was running, this time L's T123 is started.
Change-Id: Id647511a4b18e0c4de0e66fb1f35dc9adb9177db
diff --git a/src/tdef.c b/src/tdef.c
index 7e79d68..692e2cf 100644
--- a/src/tdef.c
+++ b/src/tdef.c
@@ -220,7 +220,7 @@
*
* struct osmo_tdef_state_timeout my_fsm_timeouts[32] = {
* [MY_FSM_STATE_3] = { .T = 423 }, // look up timeout configured for T423
- * [MY_FSM_STATE_7] = { .T = 235 },
+ * [MY_FSM_STATE_7] = { .keep_timer = true, .T = 235 }, // keep previous timer if running, or start T235
* [MY_FSM_STATE_8] = { .keep_timer = true }, // keep previous state's T number, continue timeout.
* // any state that is omitted will remain zero == no timeout
* };
@@ -254,20 +254,25 @@
const char *file, int line)
{
const struct osmo_tdef_state_timeout *t = osmo_tdef_get_state_timeout(state, timeouts_array);
- unsigned long val;
+ unsigned long val = 0;
/* No timeout defined for this state? */
if (!t)
return _osmo_fsm_inst_state_chg(fi, state, 0, 0, file, line);
+ if (t->T)
+ val = osmo_tdef_get(tdefs, t->T, OSMO_TDEF_S, default_timeout);
+
if (t->keep_timer) {
- int rc = _osmo_fsm_inst_state_chg_keep_timer(fi, state, file, line);
- if (t->T && !rc)
- fi->T = t->T;
- return rc;
+ if (t->T)
+ return _osmo_fsm_inst_state_chg_keep_or_start_timer(fi, state, val, t->T, file, line);
+ else
+ return _osmo_fsm_inst_state_chg_keep_timer(fi, state, file, line);
}
- val = osmo_tdef_get(tdefs, t->T, OSMO_TDEF_S, default_timeout);
+ /* val is always initialized here, because if t->keep_timer is false, t->T must be != 0.
+ * Otherwise osmo_tdef_get_state_timeout() would have returned NULL. */
+ OSMO_ASSERT(t->T);
return _osmo_fsm_inst_state_chg(fi, state, val, t->T, file, line);
}