Merge branch 'issue_13300' into 'master'

Increase the notes polling timeout over time

Originally by @roperzh at https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2821

Fixes #13300 

See merge request !3071

CHANGELOG

@@ -11,6 +11,7 @@ v 8.6.0 (unreleased)
   - Update documentation to reflect Guest role not being enforced on internal projects
   - Allow search for logged out users
   - Don't show Issues/MRs from archived projects in Groups view
+  - Increase the notes polling timeout over time (Roberto Dip)
 v 8.5.3
   - Flush repository caches before renaming projects

app/assets/javascripts/notes.js.coffee

@@ -16,10 +16,12 @@ class @Notes
     @view = view
     @noteable_url = document.URL
     @notesCountBadge ||= $(".issuable-details").find(".notes-tab .badge")
+    @basePollingInterval = 15000
+    @maxPollingSteps = 4
     @cleanBinding()
     @addBinding()
-    @initRefresh()
+    @setPollingInterval()
     @setupMainTargetNoteForm()
     @initTaskList()
@@ -91,9 +93,11 @@ class @Notes
     clearInterval(Notes.interval)
     Notes.interval = setInterval =>
       @refresh()
-    , 15000
+    , @pollingInterval
   refresh: ->
+    return if @refreshing is true
+    refreshing = true
     if not document.hidden and document.URL.indexOf(@noteable_url) is 0
       @getContent()
@@ -105,12 +109,31 @@ class @Notes
       success: (data) =>
         notes = data.notes
         @last_fetched_at = data.last_fetched_at
+        @setPollingInterval(data.notes.length)
         $.each notes, (i, note) =>
           if note.discussion_with_diff_html?
             @renderDiscussionNote(note)
           else
             @renderNote(note)
+      always: =>
+        @refreshing = false
+
+  ###
+  Increase @pollingInterval up to 120 seconds on every function call,
+  if `shouldReset` has a truthy value, 'null' or 'undefined' the variable
+  will reset to @basePollingInterval.
+  Note: this function is used to gradually increase the polling interval
+  if there aren't new notes coming from the server
+  ###
+  setPollingInterval: (shouldReset = true) ->
+    nthInterval = @basePollingInterval * Math.pow(2, @maxPollingSteps - 1)
+    if shouldReset
+      @pollingInterval = @basePollingInterval
+    else if @pollingInterval < nthInterval
+      @pollingInterval *= 2
+
+    @initRefresh()
   ###
   Render note in main comments area.