Only tokenize in background if when a buffer is visible in an editor

This will prevent running a bunch of background tokenization when Atom is reloaded. We only perform tokenization to support content that is actually on screen.

spec/app/tokenized-buffer-spec.coffee

@@ -21,6 +21,7 @@ describe "TokenizedBuffer", ->
       editSession = fixturesProject.buildEditSessionForPath('sample.js', autoIndent: false)
       buffer = editSession.buffer
       tokenizedBuffer = editSession.displayBuffer.tokenizedBuffer
+      editSession.setVisible(true)
       changeHandler = jasmine.createSpy('changeHandler')
       tokenizedBuffer.on "change", changeHandler
 
@@ -289,6 +290,7 @@ describe "TokenizedBuffer", ->
       editSession = fixturesProject.buildEditSessionForPath('sample-with-tabs.coffee', { tabLength })
       buffer = editSession.buffer
       tokenizedBuffer = editSession.displayBuffer.tokenizedBuffer
+      editSession.setVisible(true)
 
     afterEach ->
       editSession.destroy()

src/app/display-buffer.coffee

@@ -27,6 +27,8 @@ class DisplayBuffer
     @buildLineMap()
     @tokenizedBuffer.on 'change', (e) => @handleTokenizedBufferChange(e)
 
+  setVisible: (visible) -> @tokenizedBuffer.setVisible(visible)
+
   buildLineMap: ->
     @lineMap = new LineMap
     @lineMap.insertAtScreenRow 0, @buildLinesForBufferRows(0, @buffer.getLastRow())

src/app/edit-session.coffee

@@ -91,6 +91,8 @@ class EditSession
       @scrollLeft == other.getScrollLeft() and
       @getCursorScreenPosition().isEqual(other.getCursorScreenPosition())
 
+  setVisible: (visible) -> @displayBuffer.setVisible(visible)
+
   setScrollTop: (@scrollTop) ->
   getScrollTop: -> @scrollTop
 

src/app/editor.coffee

@@ -422,6 +422,7 @@ class Editor extends View
       @activeEditSession.off()
 
     @activeEditSession = @editSessions[index]
+    @activeEditSession.setVisible(true)
 
     @activeEditSession.on "buffer-contents-change-on-disk", =>
       @showBufferConflictAlert(@activeEditSession)

src/app/tokenized-buffer.coffee

@@ -16,6 +16,7 @@ class TokenizedBuffer
   screenLines: null
   chunkSize: 50
   invalidRows: null
+  visible: false
 
   constructor: (@buffer, { @languageMode, @tabLength }) ->
     @tabLength ?= 2
@@ -25,6 +26,9 @@ class TokenizedBuffer
     @invalidateRow(0)
     @buffer.on "change.tokenized-buffer#{@id}", (e) => @handleBufferChange(e)
 
+  setVisible: (@visible) ->
+    @tokenizeInBackground() if @visible
+
   getTabLength: ->
     @tabLength
 
@@ -35,7 +39,7 @@ class TokenizedBuffer
     @trigger "change", { start: 0, end: lastRow, delta: 0 }
 
   tokenizeInBackground: ->
-    return if @pendingChunk
+    return if not @visible or @pendingChunk
     @pendingChunk = true
     _.defer =>
       @pendingChunk = false