Simulate games in background while playing levels if we think there's extra compute power

app/core/initialize.coffee

@@ -71,7 +71,7 @@ setUpBackboneMediator = ->
   if false  # Debug which events are being fired
     originalPublish = Backbone.Mediator.publish
     Backbone.Mediator.publish = ->
-      console.log 'Publishing event:', arguments...
+      console.log 'Publishing event:', arguments... unless /(tick|frame-changed)/.test(arguments[0])
       originalPublish.apply Backbone.Mediator, arguments
 
 setUpMoment = ->

app/lib/Angel.coffee

@@ -25,9 +25,10 @@ module.exports = class Angel extends CocoClass
     super()
     @say 'Got my wings.'
     isIE = window.navigator and (window.navigator.userAgent.search('MSIE') isnt -1 or window.navigator.appName is 'Microsoft Internet Explorer')
-    if isIE or @shared.headless
+    slowerSimulations = isIE  #or @shared.headless
-      # Since IE is so slow to serialize without transferable objects, we can't trust it.
+    # Since IE is so slow to serialize without transferable objects, we can't trust it.
-      # We also noticed the headless_client simulator needing more time. (This does both Simulators, though.)
+    # We also noticed the headless_client simulator needing more time. (This does both Simulators, though.) If we need to use lots of headless clients, enable this.
+    if slowerSimulations
       @infiniteLoopIntervalDuration *= 10
       @infiniteLoopTimeoutDuration *= 10
       @abortTimeoutDuration *= 10
@@ -89,7 +90,7 @@ module.exports = class Angel extends CocoClass
 
       # We have to abort like an infinite loop if we see one of these; they're not really recoverable
       when 'non-user-code-problem'
-        Backbone.Mediator.publish 'god:non-user-code-problem', problem: event.data.problem
+        Backbone.Mediator.publish 'god:non-user-code-problem', problem: event.data.problem, god: @shared.god
         if @shared.firstWorld
           @infinitelyLooped(false, true)  # For now, this should do roughly the right thing if it happens during load.
         else
@@ -108,9 +109,9 @@ module.exports = class Angel extends CocoClass
       when 'console-log'
         @log event.data.args...
       when 'user-code-problem'
-        Backbone.Mediator.publish 'god:user-code-problem', problem: event.data.problem
+        Backbone.Mediator.publish 'god:user-code-problem', problem: event.data.problem, god: @shared.god
       when 'world-load-progress-changed'
-        Backbone.Mediator.publish 'god:world-load-progress-changed', progress: event.data.progress
+        Backbone.Mediator.publish 'god:world-load-progress-changed', progress: event.data.progress, god: @shared.god
         unless event.data.progress is 1 or @work.preload or @work.headless or @work.synchronous or @deserializationQueue.length or (@shared.firstWorld and not @shared.spectate)
           @worker.postMessage func: 'serializeFramesSoFar'  # Stream it!
 
@@ -126,7 +127,8 @@ module.exports = class Angel extends CocoClass
 
   beholdGoalStates: (goalStates, overallStatus, preload=false) ->
     return if @aborting
-    Backbone.Mediator.publish 'god:goals-calculated', goalStates: goalStates, preload: preload, overallStatus: overallStatus
+    Backbone.Mediator.publish 'god:goals-calculated', goalStates: goalStates, preload: preload, overallStatus: overallStatus, god: @shared.god
+    @shared.god.trigger 'goals-calculated', goalStates: goalStates, preload: preload, overallStatus: overallStatus
     @finishWork() if @shared.headless
 
   beholdWorld: (serialized, goalStates, startFrame, endFrame, streamingWorld) ->
@@ -176,8 +178,9 @@ module.exports = class Angel extends CocoClass
     return if @aborting
     problem = type: 'runtime', level: 'error', id: 'runtime_InfiniteLoop', message: 'Code never finished. It\'s either really slow or has an infinite loop.'
     problem.message = 'Escape pressed; code aborted.' if escaped
-    Backbone.Mediator.publish 'god:user-code-problem', problem: problem
+    Backbone.Mediator.publish 'god:user-code-problem', problem: problem, god: @shared.god
-    Backbone.Mediator.publish 'god:infinite-loop', firstWorld: @shared.firstWorld, nonUserCodeProblem: nonUserCodeProblem
+    Backbone.Mediator.publish 'god:infinite-loop', firstWorld: @shared.firstWorld, nonUserCodeProblem: nonUserCodeProblem, god: @shared.god
+    @shared.god.trigger 'infinite-loop', firstWorld: @shared.firstWorld, nonUserCodeProblem: nonUserCodeProblem  # For Simulator. TODO: refactor all the god:* Mediator events to be local events.
     @reportLoadError() if nonUserCodeProblem
     @fireWorker()
 
@@ -308,7 +311,7 @@ module.exports = class Angel extends CocoClass
     i = 0
     while i < work.testWorld.totalFrames
       frame = work.testWorld.getFrame i++
-    Backbone.Mediator.publish 'god:world-load-progress-changed', progress: 1
+    Backbone.Mediator.publish 'god:world-load-progress-changed', progress: 1, god: @shared.god
     work.testWorld.ended = true
     system.finish work.testWorld.thangs for system in work.testWorld.systems
     work.t2 = now()

app/lib/God.coffee

@@ -25,6 +25,7 @@ module.exports = class God extends CocoClass
       workerCode: options.workerCode or '/javascripts/workers/worker_world.js'  # Either path or function
       headless: options.headless  # Whether to just simulate the goals, or to deserialize all simulation results
       spectate: options.spectate
+      god: @
       godNick: @nick
       workQueue: []
       firstWorld: true
@@ -61,6 +62,7 @@ module.exports = class God extends CocoClass
   setWorldClassMap: (worldClassMap) -> @angelsShare.worldClassMap = worldClassMap
 
   onTomeCast: (e) ->
+    return unless e.god is @
     @lastSubmissionCount = e.submissionCount
     @lastFlagHistory = (flag for flag in e.flagHistory when flag.source isnt 'code')
     @lastDifficulty = e.difficulty
@@ -142,9 +144,9 @@ module.exports = class God extends CocoClass
       when 'console-log'
         console.log "|#{@nick}'s debugger|", event.data.args...
       when 'debug-value-return'
-        Backbone.Mediator.publish 'god:debug-value-return', event.data.serialized
+        Backbone.Mediator.publish 'god:debug-value-return', event.data.serialized, god: @
       when 'debug-world-load-progress-changed'
-        Backbone.Mediator.publish 'god:debug-world-load-progress-changed', progress: event.data.progress
+        Backbone.Mediator.publish 'god:debug-world-load-progress-changed', progress: event.data.progress, god: @
 
   onNewWorldCreated: (e) ->
     @currentUserCodeMap = @filterUserCodeMapWhenFromWorld e.world.userCodeMap

app/lib/simulator/Simulator.coffee

@@ -45,6 +45,7 @@ module.exports = class Simulator extends CocoClass
         humansGameID: humanGameID
         ogresGameID: ogresGameID
         simulator: @simulator
+        background: Boolean(@options.background)
       error: (errorData) ->
         console.warn "There was an error fetching two games! #{JSON.stringify errorData}"
         if errorData?.responseText?.indexOf("Old simulator") isnt -1
@@ -84,8 +85,8 @@ module.exports = class Simulator extends CocoClass
       @handleSingleSimulationError error
 
   commenceSingleSimulation: ->
-    Backbone.Mediator.subscribeOnce 'god:infinite-loop', @handleSingleSimulationInfiniteLoop, @
+    @listenToOnce @god, 'infinite-loop', @handleSingleSimulationInfiniteLoop
-    Backbone.Mediator.subscribeOnce 'god:goals-calculated', @processSingleGameResults, @
+    @listenToOnce @god, 'goals-calculated', @processSingleGameResults
     @god.createWorld @generateSpellsObject()
 
   handleSingleSimulationError: (error) ->
@@ -96,7 +97,7 @@ module.exports = class Simulator extends CocoClass
       process.exit(0)
     @cleanupAndSimulateAnotherTask()
 
-  handleSingleSimulationInfiniteLoop: ->
+  handleSingleSimulationInfiniteLoop: (e) ->
     console.log 'There was an infinite loop in the single game!'
     return if @destroyed
     if @options.headlessClient and @options.simulateOnlyOneGame
@@ -105,7 +106,6 @@ module.exports = class Simulator extends CocoClass
     @cleanupAndSimulateAnotherTask()
 
   processSingleGameResults: (simulationResults) ->
-    return console.error "Weird, we destroyed the Simulator before it processed results?" if @destroyed
     try
       taskResults = @formTaskResultsObject simulationResults
     catch error
@@ -165,6 +165,7 @@ module.exports = class Simulator extends CocoClass
     @simulateAnotherTaskAfterDelay()
 
   handleNoGamesResponse: ->
+    @noTasks = true
     info = 'Finding game to simulate...'
     console.log info
     @trigger 'statusUpdate', info
@@ -223,7 +224,7 @@ module.exports = class Simulator extends CocoClass
     @god.setLevel @level.serialize(@supermodel, @session, @otherSession)
     @god.setLevelSessionIDs (session.sessionID for session in @task.getSessions())
     @god.setWorldClassMap @world.classMap
-    @god.setGoalManager new GoalManager(@world, @level.get 'goals')
+    @god.setGoalManager new GoalManager @world, @level.get('goals'), null, {headless: true}
     humanFlagHistory = _.filter @session.get('state')?.flagHistory ? [], (event) => event.source isnt 'code' and event.team is (@session.get('team') ? 'humans')
     ogreFlagHistory = _.filter @otherSession.get('state')?.flagHistory ? [], (event) => event.source isnt 'code' and event.team is (@otherSession.get('team') ? 'ogres')
     @god.lastFlagHistory = humanFlagHistory.concat ogreFlagHistory
@@ -232,8 +233,8 @@ module.exports = class Simulator extends CocoClass
     @god.lastDifficulty = 0
 
   commenceSimulationAndSetupCallback: ->
-    Backbone.Mediator.subscribeOnce 'god:infinite-loop', @onInfiniteLoop, @
+    @listenToOnce @god, 'infinite-loop', @onInfiniteLoop
-    Backbone.Mediator.subscribeOnce 'god:goals-calculated', @processResults, @
+    @listenToOnce @god, 'goals-calculated', @processResults
     @god.createWorld @generateSpellsObject()
 
     # Search for leaks, headless-client only.
@@ -260,14 +261,13 @@ module.exports = class Simulator extends CocoClass
                 process.exit()
               @hd = new @memwatch.HeapDiff()
 
-  onInfiniteLoop: ->
+  onInfiniteLoop: (e) ->
     return if @destroyed
     console.warn 'Skipping infinitely looping game.'
     @trigger 'statusUpdate', "Infinite loop detected; grabbing a new game in #{@retryDelayInSeconds} seconds."
     _.delay @cleanupAndSimulateAnotherTask, @retryDelayInSeconds * 1000
 
   processResults: (simulationResults) ->
-    return console.error "Weird, we destroyed the Simulator before it processed results?" if @destroyed
     try
       taskResults = @formTaskResultsObject simulationResults
     catch error
@@ -317,9 +317,13 @@ module.exports = class Simulator extends CocoClass
   cleanupAndSimulateAnotherTask: =>
     return if @destroyed
     @cleanupSimulation()
-    @fetchAndSimulateTask()
+    if @options.background or @noTasks
+      @fetchAndSimulateOneGame()
+    else
+      @fetchAndSimulateTask()
 
   cleanupSimulation: ->
+    @stopListening @god
     @world = null
     @level = null
 

app/lib/world/GoalManager.coffee

@@ -16,8 +16,9 @@ module.exports = class GoalManager extends CocoClass
   nextGoalID: 0
   nicks: ['GoalManager']
 
-  constructor: (@world, @initialGoals, @team) ->
+  constructor: (@world, @initialGoals, @team, options) ->
     super()
+    @options = options or {}
     @init()
 
   init: ->
@@ -107,6 +108,7 @@ module.exports = class GoalManager extends CocoClass
     @addNewSubscription(channel, f(channel))
 
   notifyGoalChanges: ->
+    return if @options.headless
     overallStatus = @checkOverallStatus()
     event =
       goalStates: @goalStates

app/models/SuperModel.coffee

@@ -199,7 +199,6 @@ module.exports = class SuperModel extends Backbone.Model
     @progress = newProg
     @trigger('update-progress', @progress)
     @trigger('loaded-all') if @finished()
-    Backbone.Mediator.publish 'supermodel:load-progress-changed', progress: @progress
 
   setMaxProgress: (@maxProgress) ->
   resetProgress: -> @progress = 0

app/schemas/subscriptions/god.coffee

@@ -27,13 +27,16 @@ worldUpdatedEventSchema = c.object {required: ['world', 'firstWorld', 'goalState
   finished: {type: 'boolean'}
 
 module.exports =
-  'god:user-code-problem': c.object {required: ['problem']},
+  'god:user-code-problem': c.object {required: ['problem', 'god']},
+    god: {type: 'object'}
     problem: {type: 'object'}
 
-  'god:non-user-code-problem': c.object {required: ['problem']},
+  'god:non-user-code-problem': c.object {required: ['problem', 'god']},
+    god: {type: 'object'}
     problem: {type: 'object'}
 
-  'god:infinite-loop': c.object {required: ['firstWorld']},
+  'god:infinite-loop': c.object {required: ['firstWorld', 'god']},
+    god: {type: 'object'}
     firstWorld: {type: 'boolean'}
     nonUserCodeProblem: {type: 'boolean'}
 
@@ -41,17 +44,21 @@ module.exports =
 
   'god:streaming-world-updated': worldUpdatedEventSchema
 
-  'god:goals-calculated': c.object {required: ['goalStates']},
+  'god:goals-calculated': c.object {required: ['goalStates', 'god']},
+    god: {type: 'object'}
     goalStates: goalStatesSchema
     preload: {type: 'boolean'}
     overallStatus: {type: ['string', 'null'], enum: ['success', 'failure', 'incomplete', null]}
 
-  'god:world-load-progress-changed': c.object {required: ['progress']},
+  'god:world-load-progress-changed': c.object {required: ['progress', 'god']},
+    god: {type: 'object'}
     progress: {type: 'number', minimum: 0, maximum: 1}
 
-  'god:debug-world-load-progress-changed': c.object {required: ['progress']},
+  'god:debug-world-load-progress-changed': c.object {required: ['progress', 'god']},
+    god: {type: 'object'}
     progress: {type: 'number', minimum: 0, maximum: 1}
 
-  'god:debug-value-return': c.object {required: ['key']},
+  'god:debug-value-return': c.object {required: ['key', 'god']},
+    god: {type: 'object'}
     key: {type: 'string'}
     value: {}

app/schemas/subscriptions/misc.coffee

@@ -48,9 +48,6 @@ module.exports =
     session: {type: 'object'}
     level: {type: 'object'}
 
-  'supermodel:load-progress-changed': c.object {required: ['progress']},
-    progress: {type: 'number', minimum: 0, maximum: 1}
-
   'buy-gems-modal:update-products': { }
 
   'buy-gems-modal:purchase-initiated': c.object {required: ['productID']},

app/schemas/subscriptions/tome.coffee

@@ -7,13 +7,14 @@ module.exports =
     preload: {type: 'boolean'}
     realTime: {type: 'boolean'}
 
-  'tome:cast-spells': c.object {title: 'Cast Spells', description: 'Published when spells are cast', required: ['spells', 'preload', 'realTime', 'submissionCount', 'flagHistory', 'difficulty']},
+  'tome:cast-spells': c.object {title: 'Cast Spells', description: 'Published when spells are cast', required: ['spells', 'preload', 'realTime', 'submissionCount', 'flagHistory', 'difficulty', 'god']},
-    spells: [type: 'object']
+    spells: {type: 'object'}
-    preload: [type: 'boolean']
+    preload: {type: 'boolean'}
-    realTime: [type: 'boolean']
+    realTime: {type: 'boolean'}
-    submissionCount: [type: 'integer']
+    submissionCount: {type: 'integer'}
-    flagHistory: [type: 'array']
+    flagHistory: {type: 'array'}
-    difficulty: [type: 'integer']
+    difficulty: {type: 'integer'}
+    god: {type: 'object'}
 
   'tome:manual-cast': c.object {title: 'Manually Cast Spells', description: 'Published when you wish to manually recast all spells', required: []},
     realTime: {type: 'boolean'}

app/views/ladder/SimulateTabView.coffee

@@ -16,12 +16,7 @@ module.exports = class SimulateTabView extends CocoView
     @simulatorsLeaderboardData = new SimulatorsLeaderboardData(me)
     @simulatorsLeaderboardDataRes = @supermodel.addModelResource(@simulatorsLeaderboardData, 'top_simulators', {cache: false})
     @simulatorsLeaderboardDataRes.load()
-    require 'vendor/aether-javascript'
+    require "vendor/aether-#{codeLanguage}" for codeLanguage in ['javascript', 'python', 'coffeescript', 'lua', 'clojure', 'io']
-    require 'vendor/aether-python'
-    require 'vendor/aether-coffeescript'
-    require 'vendor/aether-lua'
-    require 'vendor/aether-clojure'
-    require 'vendor/aether-io'
 
   onLoaded: ->
     super()

app/views/play/SpectateView.coffee

@@ -187,7 +187,7 @@ module.exports = class SpectateLevelView extends RootView
   # callbacks
 
   onInfiniteLoop: (e) ->
-    return unless e.firstWorld
+    return unless e.firstWorld and e.god is @god
     @openModalView new InfiniteLoopModal()
     window.tracker?.trackEvent 'Saw Initial Infinite Loop', level: @world.name, label: @world.name
 

app/views/play/level/LevelLoadingView.coffee

@@ -44,12 +44,14 @@ module.exports = class LevelLoadingView extends CocoView
       @$el.addClass('manually-sized').css('height', newHeight)
 
   onLevelLoaded: (e) ->
+    return if @level
     @level = e.level
     @prepareGoals e
     @prepareTip()
     @prepareIntro()
 
   onSessionLoaded: (e) ->
+    return if @session
     @session = e.session if e.session.get('creator') is me.id
 
   prepareGoals: (e) ->

app/views/play/level/PlayLevelView.coffee

@@ -19,6 +19,7 @@ LevelComponent = require 'models/LevelComponent'
 Article = require 'models/Article'
 Camera = require 'lib/surface/Camera'
 AudioPlayer = require 'lib/AudioPlayer'
+Simulator = require 'lib/simulator/Simulator'
 
 # subviews
 LevelLoadingView = require './LevelLoadingView'
@@ -139,11 +140,11 @@ module.exports = class PlayLevelView extends RootView
   trackLevelLoadEnd: ->
     return if @isEditorPreview
     @loadEndTime = new Date()
-    loadDuration = @loadEndTime - @loadStartTime
+    @loadDuration = @loadEndTime - @loadStartTime
-    console.debug "Level unveiled after #{(loadDuration / 1000).toFixed(2)}s"
+    console.debug "Level unveiled after #{(@loadDuration / 1000).toFixed(2)}s"
     unless @observing
-      application.tracker?.trackEvent 'Finished Level Load', category: 'Play Level', label: @levelID, level: @levelID, loadDuration: loadDuration
+      application.tracker?.trackEvent 'Finished Level Load', category: 'Play Level', label: @levelID, level: @levelID, loadDuration: @loadDuration
-      application.tracker?.trackTiming loadDuration, 'Level Load Time', @levelID, @levelID
+      application.tracker?.trackTiming @loadDuration, 'Level Load Time', @levelID, @levelID
 
   # CocoView overridden methods ###############################################
 
@@ -195,6 +196,7 @@ module.exports = class PlayLevelView extends RootView
       @worldLoadFakeResources.push @supermodel.addSomethingResource "world_simulation_#{percent}%", 1
 
   onWorldLoadProgressChanged: (e) ->
+    return unless e.god is @god
     return unless @worldLoadFakeResources
     @lastWorldLoadPercent ?= 0
     worldLoadPercent = Math.floor 100 * e.progress
@@ -240,7 +242,7 @@ module.exports = class PlayLevelView extends RootView
     @god.setGoalManager @goalManager
 
   insertSubviews: ->
-    @insertSubView @tome = new TomeView levelID: @levelID, session: @session, otherSession: @otherSession, thangs: @world.thangs, supermodel: @supermodel, level: @level, observing: @observing, courseID: @courseID, courseInstanceID: @courseInstanceID
+    @insertSubView @tome = new TomeView levelID: @levelID, session: @session, otherSession: @otherSession, thangs: @world.thangs, supermodel: @supermodel, level: @level, observing: @observing, courseID: @courseID, courseInstanceID: @courseInstanceID, god: @god
     @insertSubView new LevelPlaybackView session: @session, level: @level
     @insertSubView new GoalsView {}
     @insertSubView new LevelFlagsView levelID: @levelID, world: @world if @$el.hasClass 'flags'
@@ -273,6 +275,7 @@ module.exports = class PlayLevelView extends RootView
   # Load Completed Setup ######################################################
 
   onSessionLoaded: (e) ->
+    return if @session
     Backbone.Mediator.publish "ipad:language-chosen", language: e.session.get('codeLanguage') ? "python"
     # Just the level and session have been loaded by the level loader
     if e.level.get('slug') is 'zero-sum'
@@ -288,7 +291,7 @@ module.exports = class PlayLevelView extends RootView
       e.session.set 'heroConfig', {"thangType":raider,"inventory":{}}
     else if e.level.get('type', true) in ['hero', 'hero-ladder', 'hero-coop'] and not _.size e.session.get('heroConfig')?.inventory ? {}
       @setupManager?.destroy()
-      @setupManager = new LevelSetupManager({supermodel: @supermodel, level: @level, levelID: @levelID, parent: @, session: @session, courseID: @courseID, courseInstanceID: @courseInstanceID})
+      @setupManager = new LevelSetupManager({supermodel: @supermodel, level: e.level, levelID: @levelID, parent: @, session: e.session, courseID: @courseID, courseInstanceID: @courseInstanceID})
       @setupManager.open()
 
     @onRealTimeMultiplayerLevelLoaded e.session if e.level.get('type') in ['hero-ladder', 'course-ladder']
@@ -365,6 +368,7 @@ module.exports = class PlayLevelView extends RootView
     # TODO: Is it possible to create a Mongoose ObjectId for 'ls', instead of the string returned from get()?
     application.tracker?.trackEvent 'Started Level', category:'Play Level', levelID: @levelID, ls: @session?.get('_id') unless @observing
     $(window).trigger 'resize'
+    _.delay (=> @perhapsStartSimulating?()), 10 * 1000
 
   playAmbientSound: ->
     return if @destroyed
@@ -384,6 +388,65 @@ module.exports = class PlayLevelView extends RootView
     Backbone.Mediator.publish 'level:suppress-selection-sounds', suppress: false
     @surface.focusOnHero()
 
+  perhapsStartSimulating: ->
+    return unless @shouldSimulate()
+    require "vendor/aether-#{codeLanguage}" for codeLanguage in ['javascript', 'python', 'coffeescript', 'lua', 'clojure', 'io']
+    @simulateNextGame()
+
+  simulateNextGame: ->
+    return @simulator.fetchAndSimulateOneGame() if @simulator
+    @simulator = new Simulator background: true
+    # Crude method of mitigating Simulator memory leak issues
+    fetchAndSimulateOneGameOriginal = @simulator.fetchAndSimulateOneGame
+    @simulator.fetchAndSimulateOneGame = =>
+      if @simulator.simulatedByYou >= 10
+        console.log '------------------- Destroying Simulator and making a new one -----------------'
+        @simulator.destroy()
+        @simulator = null
+        @simulateNextGame()
+      else
+        fetchAndSimulateOneGameOriginal.apply @simulator
+    @simulator.fetchAndSimulateOneGame()
+
+  shouldSimulate: ->
+    # Crude heuristics are crude.
+    defaultCores = 2
+    cores = window.navigator.hardwareConcurrency or defaultCores  # Available on Chrome/Opera, soon Safari
+    defaultHeapLimit = 793000000
+    heapLimit = window.performance?.memory?.jsHeapSizeLimit or defaultHeapLimit  # Only available on Chrome, basically just says 32- vs. 64-bit
+    levelType = @level.get 'type', true
+    gamesSimulated = me.get('simulatedBy')
+    console.debug "Should we start simulating? Cores:", window.navigator.hardwareConcurrency, "Heap limit:", window.performance?.memory?.jsHeapSizeLimit, "Load duration:", @loadDuration
+    return false unless $.browser?.desktop
+    return false if $.browser?.msie or $.browser?.msedge
+    return false if $.browser.linux
+    return false if me.level() < 8
+    if levelType is 'course'
+      return false
+    else if levelType is 'hero' and gamesSimulated
+      return false if cores < 8
+      return false if heapLimit < defaultHeapLimit
+      return false if @loadDuration > 10000
+    else if levelType is 'hero-ladder' and gamesSimulated
+      return false if cores < 4
+      return false if heapLimit < defaultHeapLimit
+      return false if @loadDuration > 15000
+    else if levelType is 'hero-ladder' and not gamesSimulated
+      return false if cores < 8
+      return false if heapLimit <= defaultHeapLimit
+      return false if @loadDuration > 20000
+    else if levelType is 'course-ladder'
+      return false if cores <= defaultCores
+      return false if heapLimit < defaultHeapLimit
+      return false if @loadDuration > 18000
+    else
+      console.warn "Unwritten level type simulation heuristics; fill these in for new level type #{levelType}?"
+      return false if cores < 8
+      return false if heapLimit < defaultHeapLimit
+      return false if @loadDuration > 10000
+    console.debug "We should have the power. Begin background ladder simulation."
+    true
+
   # callbacks
 
   onCtrlS: (e) ->
@@ -457,7 +520,7 @@ module.exports = class PlayLevelView extends RootView
     application.tracker?.trackEvent 'Confirmed Restart', category: 'Play Level', level: @level.get('name'), label: @level.get('name') unless @observing
 
   onInfiniteLoop: (e) ->
-    return unless e.firstWorld
+    return unless e.firstWorld and e.god is @god
     @openModalView new InfiniteLoopModal nonUserCodeProblem: e.nonUserCodeProblem
     application.tracker?.trackEvent 'Saw Initial Infinite Loop', category: 'Play Level', level: @level.get('name'), label: @level.get('name') unless @observing
 
@@ -557,6 +620,7 @@ module.exports = class PlayLevelView extends RootView
     @goalManager?.destroy()
     @scriptManager?.destroy()
     @setupManager?.destroy()
+    @simulator?.destroy()
     if ambientSound = @ambientSound
       # Doesn't seem to work; stops immediately.
       createjs.Tween.get(ambientSound).to({volume: 0.0}, 1500).call -> ambientSound.stop()

app/views/play/level/tome/CastButtonView.coffee

@@ -123,6 +123,7 @@ module.exports = class CastButtonView extends CocoView
 
   onGoalsCalculated: (e) ->
     # When preloading, with real-time playback enabled, we highlight the submit button when we think they'll win.
+    return unless e.god is @god
     return unless e.preload
     return if @options.level.get 'hidesRealTimePlayback'
     return if @options.level.get('slug') in ['course-thornbush-farm', 'thornbush-farm']  # Don't show it until they actually win for this first one.

app/views/play/level/tome/Spell.coffee

@@ -47,7 +47,7 @@ module.exports = class Spell
       @source = @originalSource = p.aiSource
     @thangs = {}
     if @canRead()  # We can avoid creating these views if we'll never use them.
-      @view = new SpellView {spell: @, level: options.level, session: @session, otherSession: @otherSession, worker: @worker}
+      @view = new SpellView {spell: @, level: options.level, session: @session, otherSession: @otherSession, worker: @worker, god: options.god}
       @view.render()  # Get it ready and code loaded in advance
       @tabView = new SpellListTabEntryView spell: @, supermodel: @supermodel, codeLanguage: @language, level: options.level
       @tabView.render()

app/views/play/level/tome/SpellView.coffee

@@ -883,6 +883,7 @@ module.exports = class SpellView extends CocoView
     @spellHasChanged = false
 
   onUserCodeProblem: (e) ->
+    return unless e.god is @options.god
     return @onInfiniteLoop e if e.problem.id is 'runtime_InfiniteLoop'
     return unless e.problem.userInfo.methodName is @spell.name
     return unless spellThang = _.find @spell.thangs, (spellThang, thangID) -> thangID is e.problem.userInfo.thangID
@@ -893,6 +894,7 @@ module.exports = class SpellView extends CocoView
       @updateAether false, false
 
   onNonUserCodeProblem: (e) ->
+    return unless e.god is @options.god
     return unless @spellThang
     problem = @spellThang.aether.createUserCodeProblem type: 'runtime', kind: 'Unhandled', message: "Unhandled error: #{e.problem.message}"
     @spellThang.aether.addProblem problem

app/views/play/level/tome/TomeView.coffee

@@ -62,7 +62,7 @@ module.exports = class TomeView extends CocoView
     @createSpells programmableThangs, programmableThangs[0]?.world  # Do before spellList, thangList, and castButton
     unless @options.level.get('type', true) in ['hero', 'hero-ladder', 'hero-coop', 'course', 'course-ladder']
       @spellList = @insertSubView new SpellListView spells: @spells, supermodel: @supermodel, level: @options.level
-    @castButton = @insertSubView new CastButtonView spells: @spells, level: @options.level, session: @options.session
+    @castButton = @insertSubView new CastButtonView spells: @spells, level: @options.level, session: @options.session, god: @options.god
     @teamSpellMap = @generateTeamSpellMap(@spells)
     unless programmableThangs.length
       @cast()
@@ -136,6 +136,7 @@ module.exports = class TomeView extends CocoView
             observing: @options.observing
             levelID: @options.levelID
             level: @options.level
+            god: @options.god
 
     for thangID, spellKeys of @thangSpells
       thang = world.getThangByID thangID
@@ -168,7 +169,7 @@ module.exports = class TomeView extends CocoView
     difficulty = sessionState.difficulty ? 0
     if @options.observing
       difficulty = Math.max 0, difficulty - 1  # Show the difficulty they won, not the next one.
-    Backbone.Mediator.publish 'tome:cast-spells', spells: @spells, preload: preload, realTime: realTime, submissionCount: sessionState.submissionCount ? 0, flagHistory: sessionState.flagHistory ? [], difficulty: difficulty
+    Backbone.Mediator.publish 'tome:cast-spells', spells: @spells, preload: preload, realTime: realTime, submissionCount: sessionState.submissionCount ? 0, flagHistory: sessionState.flagHistory ? [], difficulty: difficulty, god: @options.god
 
   onToggleSpellList: (e) ->
     @spellList?.rerenderEntries()

server/queues/scoring/getTwoGames.coffee

@@ -10,7 +10,9 @@ module.exports = getTwoGames = (req, res) ->
   humansSessionID = req.body.humansGameID
   ogresSessionID = req.body.ogresGameID
   return getSpecificSessions res, humansSessionID, ogresSessionID if humansSessionID and ogresSessionID
-  getRandomSessions req.user, sendSessionsResponse(res)
+  options =
+    background: req.body.background
+  getRandomSessions req.user, options, sendSessionsResponse(res)
 
 sessionSelectionString = 'team totalScore transpiledCode submittedCodeLanguage teamSpells levelID creatorName creator submitDate leagues'
 
@@ -33,18 +35,18 @@ getSpecificSession = (sessionID, callback) ->
     if err? then return callback "Couldn\'t find target simulation session #{sessionID}"
     callback null, session
 
-getRandomSessions = (user, callback) ->
+getRandomSessions = (user, options, callback) ->
   # Determine whether to play a random match, an internal league match, or an external league match.
   # Only people in a league will end up simulating internal league matches (for leagues they're in) except by dumb chance.
   # If we don't like that, we can rework sampleByLevel to have an opportunity to switch to internal leagues if the first session had a league affiliation.
   leagueIDs = user?.get('clans') or []
   leagueIDs = leagueIDs.concat user?.get('courseInstances') or []
   leagueIDs = (leagueID + '' for leagueID in leagueIDs)  # Make sure to fetch them as strings.
-  return sampleByLevel callback unless leagueIDs.length and Math.random() > 1 / leagueIDs.length
+  return sampleByLevel options, callback unless leagueIDs.length and Math.random() > 1 / leagueIDs.length
   leagueID = _.sample leagueIDs
   findRandomSession {'leagues.leagueID': leagueID}, (err, session) ->
     if err then return callback err
-    unless session then return sampleByLevel callback
+    unless session then return sampleByLevel options, callback
     otherTeam = scoringUtils.calculateOpposingTeam session.team
     queryParameters = team: otherTeam, levelID: session.levelID
     if Math.random() < 0.5
@@ -67,8 +69,9 @@ getRandomSessions = (user, callback) ->
 # Sampling by level: we pick a level, then find a human and ogre session for that level, one at random, one biased towards recent submissions.
 #ladderLevelIDs = ['greed', 'criss-cross', 'brawlwood', 'dungeon-arena', 'gold-rush', 'sky-span']  # Let's not give any extra simulations to old ladders.
 ladderLevelIDs = ['dueling-grounds', 'cavern-survival', 'multiplayer-treasure-grove', 'harrowland', 'zero-sum', 'ace-of-coders', 'wakka-maul']
-sampleByLevel = (callback) ->
+backgroundLadderLevelIDs = _.without ladderLevelIDs, 'zero-sum', 'ace-of-coders'
-  levelID = _.sample ladderLevelIDs
+sampleByLevel = (options, callback) ->
+  levelID = _.sample(if options.background then backgroundLadderLevelIDs else ladderLevelIDs)
   favorRecentHumans = Math.random() < 0.5  # We pick one session favoring recent submissions, then find another one uniformly to play against
   async.map [{levelID: levelID, team: 'humans', favorRecent: favorRecentHumans}, {levelID: levelID, team: 'ogres', favorRecent: not favorRecentHumans}], findRandomSession, callback