(Hopefully) Lessens preferences and manifest injection lag (#30596)

* first step to fixing a potential problem is identifying it

* woops

* kk

* mso is already doing this kek

* yeah lets do that too.

* replicated code

* wups

* wups

* better

* gibe the merge b0ss

* cyberboss

* Update dummy.dm

code/modules/mob/dead/new_player/preferences_setup.dm

@@ -34,7 +34,7 @@
 				return
 
 	// Set up the dummy for its photoshoot
-	var/mob/living/carbon/human/dummy/mannequin = new()
+	var/mob/living/carbon/human/dummy/mannequin = generate_or_wait_for_human_dummy(DUMMY_HUMAN_SLOT_PREFERENCES)
 	copy_to(mannequin)
 
 	// Determine what job is marked as 'High' priority, and dress them up as such.
@@ -82,4 +82,4 @@
 	CHECK_TICK
 	preview_icon.Scale(preview_icon.Width() * 2, preview_icon.Height() * 2) // Scaling here to prevent blurring in the browser.
 	CHECK_TICK
-	qdel(mannequin)
+	unset_busy_human_dummy(DUMMY_HUMAN_SLOT_PREFERENCES)

code/modules/mob/living/carbon/human/dummy.dm

@@ -0,0 +1,43 @@
+
+/mob/living/carbon/human/dummy
+	real_name = "Test Dummy"
+	status_flags = GODMODE|CANPUSH
+	var/in_use = FALSE
+
+INITIALIZE_IMMEDIATE(/mob/living/carbon/human/dummy)
+
+/mob/living/carbon/human/dummy/Destroy()
+	in_use = FALSE
+	return ..()
+
+/mob/living/carbon/human/dummy/Life()
+	return
+
+/mob/living/carbon/human/dummy/proc/wipe_state()
+	QDEL_LIST(contents)
+	cut_overlays(TRUE)
+
+//Inefficient pooling/caching way.
+GLOBAL_LIST_EMPTY(human_dummy_list)
+
+/proc/generate_or_wait_for_human_dummy(slotkey)
+	if(!slotkey)
+		return new /mob/living/carbon/human/dummy
+	var/mob/living/carbon/human/dummy/D = GLOB.human_dummy_list[slotkey]
+	if(istype(D))
+		UNTIL(!D.in_use)
+	else
+		pass()
+	if(QDELETED(D))
+		D = new
+		GLOB.human_dummy_list[slotkey] = D
+	D.in_use = TRUE
+	return D
+
+/proc/unset_busy_human_dummy(slotnumber)
+	if(!slotnumber)
+		return
+	var/mob/living/carbon/human/dummy/D = GLOB.human_dummy_list[slotnumber]
+	if(istype(D))
+		D.wipe_state()
+		D.in_use = FALSE

code/modules/mob/living/carbon/human/human.dm

@@ -5,15 +5,6 @@
 	icon = 'icons/mob/human.dmi'
 	icon_state = "caucasian_m"
 
-/mob/living/carbon/human/dummy
-	real_name = "Test Dummy"
-	status_flags = GODMODE|CANPUSH
-
-INITIALIZE_IMMEDIATE(/mob/living/carbon/human/dummy)
-
-/mob/living/carbon/human/dummy/Life()
-	return
-
 /mob/living/carbon/human/Initialize()
 	verbs += /mob/living/proc/mob_sleep
 	verbs += /mob/living/proc/lay_down