Merge pull request #6449 from atom/ns-update-again-in-frame

Perform DOM updates requested from DOM reads in the same frame, after we finish reading

spec/text-editor-component-spec.coffee

@@ -2624,7 +2624,7 @@ describe "TextEditorComponent", ->
       expect(componentNode.querySelector('.placeholder-text')).toBeNull()
 
   describe "legacy editor compatibility", ->
-    it "triggers the screen-lines-changed event before the editor:display-update event", ->
+    it "triggers the screen-lines-changed event before the editor:display-updated event", ->
       editor.setSoftWrapped(true)
 
       callingOrder = []
@@ -2633,7 +2633,7 @@ describe "TextEditorComponent", ->
       editor.insertText("HELLO! HELLO!\n HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! HELLO! ")
       nextAnimationFrame()
 
-      expect(callingOrder).toEqual ['screen-lines-changed', 'editor:display-updated']
+      expect(callingOrder).toEqual ['screen-lines-changed', 'editor:display-updated', 'editor:display-updated']
 
     it "works with the ::setEditorHeightInLines and ::setEditorWidthInChars helpers", ->
       setEditorHeightInLines(wrapperView, 7)

spec/view-registry-spec.coffee

@@ -119,6 +119,36 @@ describe "ViewRegistry", ->
       frameRequests[0]()
       expect(events).toEqual ['write 4', 'read 3']
 
+    it "performs writes requested from read callbacks in the same animation frame", ->
+      spyOn(window, 'setInterval').andCallFake(fakeSetInterval)
+      spyOn(window, 'clearInterval').andCallFake(fakeClearInterval)
+      events = []
+
+      registry.pollDocument -> events.push('poll')
+      registry.pollAfterNextUpdate()
+      registry.updateDocument -> events.push('write 1')
+      registry.readDocument ->
+        registry.updateDocument -> events.push('write from read 1')
+        events.push('read 1')
+      registry.readDocument ->
+        registry.updateDocument -> events.push('write from read 2')
+        events.push('read 2')
+      registry.updateDocument -> events.push('write 2')
+
+      expect(frameRequests.length).toBe 1
+      frameRequests[0]()
+      expect(frameRequests.length).toBe 1
+
+      expect(events).toEqual [
+        'write 1'
+        'write 2'
+        'read 1'
+        'read 2'
+        'poll'
+        'write from read 1'
+        'write from read 2'
+      ]
+
     it "pauses DOM polling when reads or writes are pending", ->
       spyOn(window, 'setInterval').andCallFake(fakeSetInterval)
       spyOn(window, 'clearInterval').andCallFake(fakeClearInterval)

src/view-registry.coffee

@@ -44,6 +44,7 @@ module.exports =
 class ViewRegistry
   documentPollingInterval: 200
   documentUpdateRequested: false
+  documentReadInProgress: false
   performDocumentPollAfterUpdate: false
   pollIntervalHandle: null
 
@@ -161,7 +162,7 @@ class ViewRegistry
 
   updateDocument: (fn) ->
     @documentWriters.push(fn)
-    @requestDocumentUpdate()
+    @requestDocumentUpdate() unless @documentReadInProgress
     new Disposable =>
       @documentWriters = @documentWriters.filter (writer) -> writer isnt fn
 
@@ -196,9 +197,15 @@ class ViewRegistry
   performDocumentUpdate: =>
     @documentUpdateRequested = false
     writer() while writer = @documentWriters.shift()
+
+    @documentReadInProgress = true
     reader() while reader = @documentReaders.shift()
     @performDocumentPoll() if @performDocumentPollAfterUpdate
     @performDocumentPollAfterUpdate = false
+    @documentReadInProgress = false
+
+    # process updates requested as a result of reads
+    writer() while writer = @documentWriters.shift()
 
   startPollingDocument: ->
     @pollIntervalHandle = window.setInterval(@performDocumentPoll, @documentPollingInterval)