world.fps and SStimers safety check (#9478)

* tgstation/tgstation#45236

* uncomment unused

code/controllers/master.dm

@@ -234,7 +234,7 @@ GLOBAL_REAL(Master, /datum/controller/master) = new
 	// Sort subsystems by display setting for easy access.
 	sortTim(subsystems, GLOBAL_PROC_REF(cmp_subsystem_display))
 	// Set world options.
-	world.fps = CONFIG_GET(number/fps)
+	world.change_fps(CONFIG_GET(number/fps))
 	var/initialized_tod = REALTIMEOFDAY
 
 	if(sleep_offline_after_initializations)

code/game/world.dm

@@ -411,6 +411,29 @@ GLOBAL_VAR(restart_counter)
 
 /world/proc/refresh_atmos_grid()
 
+/world/proc/change_fps(new_value = 20)
+	if(new_value <= 0)
+		CRASH("change_fps() called with [new_value] new_value.")
+	if(fps == new_value)
+		return //No change required.
+
+	fps = new_value
+	on_tickrate_change()
+
+/* UNUSED. uncomment if using
+/world/proc/change_tick_lag(new_value = 0.5)
+	if(new_value <= 0)
+		CRASH("change_tick_lag() called with [new_value] new_value.")
+	if(tick_lag == new_value)
+		return //No change required.
+
+	tick_lag = new_value
+	on_tickrate_change()
+*/
+
+/world/proc/on_tickrate_change()
+	SStimer?.reset_buckets()
+
 /world/proc/init_byond_tracy()
 	var/library
 

code/modules/admin/verbs/fps.dm

@@ -23,4 +23,4 @@
 	SSblackbox.record_feedback("nested tally", "admin_toggle", 1, list("Set Server FPS", "[new_fps]")) //If you are copy-pasting this, ensure the 2nd parameter is unique to the new proc!
 
 	CONFIG_SET(number/fps, new_fps)
-	world.fps = new_fps
+	world.change_fps(new_fps)