Civ city list is now concurrency-proof

core/src/com/unciv/logic/city/CityInfo.kt

@@ -46,7 +46,7 @@ class CityInfo {
         }
 
         this.location = cityLocation
-        civInfo.cities.add(this)
+        civInfo.cities = civInfo.cities.toMutableList().apply { add(this@CityInfo) }
         if(civInfo == civInfo.gameInfo.getPlayerCivilization())
             civInfo.addNotification("$name {has been founded}!", cityLocation, Color.PURPLE)
         if (civInfo.policies.isAdopted("Legalism") && civInfo.cities.size <= 4) cityConstructions.addCultureBuilding()
@@ -184,14 +184,14 @@ class CityInfo {
     }
 
     fun destroyCity() {
-        civInfo.cities.remove(this)
+        civInfo.cities = civInfo.cities.toMutableList().apply { remove(this@CityInfo) }
         getTiles().forEach { expansion.relinquishOwnership(it) }
         getCenterTile().improvement="City ruins"
     }
 
     fun moveToCiv(newCivInfo: CivilizationInfo){
-        civInfo.cities.remove(this)
-        newCivInfo.cities.add(this)
+        civInfo.cities = civInfo.cities.toMutableList().apply { remove(this@CityInfo) }
+        newCivInfo.cities = newCivInfo.cities.toMutableList().apply { add(this@CityInfo) }
         civInfo = newCivInfo
 
         // now that the tiles have changed, we need to reassign population

core/src/com/unciv/logic/civilization/CivilizationInfo.kt

@@ -35,7 +35,11 @@ class CivilizationInfo {
     var greatPeople = GreatPersonManager()
     var scienceVictory = ScienceVictoryManager()
     var diplomacy = HashMap<String,DiplomacyManager>()
-    var cities = ArrayList<CityInfo>()
+
+    // if we only use lists, and change the list each time the cities are changed,
+    // we won't get concurrent modification exceptions.
+    // This is basically a way to ensure our lists are immutable.
+    var cities = listOf<CityInfo>()
     var exploredTiles = HashSet<Vector2>()
 
     constructor()
@@ -58,7 +62,7 @@ class CivilizationInfo {
         toReturn.greatPeople=greatPeople.clone()
         toReturn.scienceVictory = scienceVictory.clone()
         toReturn.diplomacy.putAll(diplomacy.values.map { it.clone() }.associateBy { it.otherCivName })
-        toReturn.cities.addAll(cities.map { it.clone() })
+        toReturn.cities = cities.map { it.clone() }
         toReturn.exploredTiles.addAll(exploredTiles)
         return toReturn
     }