It's re-entrant now

code/modules/spacial_allocator/zlevel.dm

@@ -0,0 +1,7 @@
+/datum/zlevel
+  var/flags = 0
+  var/dirt_count = 0
+  var/zpos
+
+/datum/zlevel/New(z)
+  zpos = z

code/modules/spacial_allocator/zlevel_manager.dm

@@ -0,0 +1,69 @@
+var/global/datum/zlev_manager/zlevels = new
+
+/datum/zlev_manager
+  // A list of z-levels
+  var/list/z_list = list()
+
+
+// Populate our z level list
+/datum/zlev_manager/proc/initialize()
+  for(var/i = 1, i < world.maxz, i++)
+    z_list.Add(new /datum/zlevel(i))
+
+
+// For when you need the z-level to be at a certain point
+/datum/zlev_manager/proc/increase_max_zlevel_to(new_maxz)
+  if(world.maxz>=new_maxz)
+    return
+  while(world.maxz<new_maxz)
+    add_new_zlevel()
+
+// Increments the max z-level by one
+// For convenience's sake returns the z-level added
+/datum/zlev_manager/proc/add_new_zlevel()
+  world.maxz++
+  var/our_z = world.maxz
+  z_list.Add(new /datum/zlevel(our_z))
+  return our_z
+
+/datum/zlev_manager/proc/cut_levels_downto(new_maxz)
+  if(world.maxz <= new_maxz)
+    return
+  while(world.maxz>new_maxz)
+    kill_topmost_zlevel()
+
+// Decrements the max z-level by one
+// not normally used, but hey the swapmap loader wanted it
+/datum/zlev_manager/proc/kill_topmost_zlevel()
+  var/our_z = world.maxz
+  qdel(z_list[our_z])
+  z_list.Remove(our_z)
+  world.maxz--
+
+/*
+* "Dirt" management
+* "Dirt" is used to keep track of whether a z level should automatically have
+* stuff on it initialize or not - the map loaders, when set to defer init, place
+* a freeze on the z levels they touch so as to prevent atmos from exploding,
+* among other things
+*/
+
+
+// Returns whether the given z level has a freeze on initialization
+/datum/zlev_manager/proc/is_zlevel_dirty(z)
+  if(z > z_list.len)
+    return 0 // It's not dirty if it's not being tracked
+  var/datum/zlevel/our_z = z_list[z]
+  return (our_z.dirt_count > 0)
+
+
+// Increases the dirt count on a z level
+/datum/zlev_manager/proc/add_dirt(z)
+  var/datum/zlevel/our_z = z_list[z]
+  our_z.dirt_count++
+
+
+// Decreases the dirt count on a z level
+/datum/zlev_manager/proc/remove_dirt(z)
+  var/datum/zlevel/our_z = z_list[z]
+  our_z.dirt_count--