rebaseline_server: fix reload delay when there is client/server clock skew

gm/rebaseline_server/static/loader.js

 /*
  * Loader:
  * Reads GM result reports written out by results.py, and imports
  * them into $scope.extraColumnHeaders and $scope.imagePairs .
  */
 var Loader = angular.module(
     'Loader',
     ['ConstantsModule', 'diff_viewer']
 );
 
@@ skipping 57 matching lines @@
 
     /**
      * On initial page load, load a full dictionary of results.
      * Once the dictionary is loaded, unhide the page elements so they can
      * render the data.
      */
     $http.get("/results/" + $scope.resultsToLoad).success(
       function(data, status, header, config) {
         var dataHeader = data[constants.KEY__HEADER];
         if (dataHeader[constants.KEY__HEADER__IS_STILL_LOADING]) {
+          // Apply the server's requested reload delay to local time,
+          // so we will wait the right number of seconds regardless of clock
+          // skew between client and server.
+          var reloadDelayInSeconds =
+              dataHeader[constants.KEY__HEADER__TIME_NEXT_UPDATE_AVAILABLE] -
+              dataHeader[constants.KEY__HEADER__TIME_UPDATED];
+          var timeNow = new Date().getTime();
+          var timeToReload = timeNow + reloadDelayInSeconds * 1000;
           $scope.loadingMessage =
               "Server is still loading results; will retry at " +
-              $scope.localTimeString(dataHeader[
-                  constants.KEY__HEADER__TIME_NEXT_UPDATE_AVAILABLE]);
+              $scope.localTimeString(timeToReload / 1000);

[borenet, 2014/03/10 17:51:14]

Why not store this in a timeToReloadInSeconds variable above to avoid the
unnecessary divide?

[epoger, 2014/03/10 18:04:47]

The problem with that, is that I would need to divide timeNow by 1000 when
computing it anyway.

          var timeNowMillis = new Date().getTime();
          var timeToReloadSeconds = (timeNowMillis / 1000) +
reloadDelayInSeconds;
          var timeToReloadMillis = timeToReloadSeconds * 1000;

So it's the same amount of work, but more lines and one more variable.

The "good" news is that rebaseline_server has 99 performance problems, and this
ain't one.

           $timeout(
               function(){location.reload();},
-              (dataHeader[constants.KEY__HEADER__TIME_NEXT_UPDATE_AVAILABLE]
-               * 1000) - new Date().getTime());
+              timeToReload - timeNow);
         } else {
           $scope.loadingMessage = "Processing data, please wait...";
 
           $scope.header = dataHeader;
           $scope.extraColumnHeaders = data[constants.KEY__EXTRACOLUMNHEADERS];
           $scope.imagePairs = data[constants.KEY__IMAGEPAIRS];
           $scope.imageSets = data[constants.KEY__IMAGESETS];
           $scope.sortColumnSubdict = constants.KEY__DIFFERENCE_DATA;
           $scope.sortColumnKey = constants.KEY__DIFFERENCE_DATA__WEIGHTED_DIFF;
 
@@ skipping 683 matching lines @@
      */
     $scope.getImageDiffRelativeUrl = function(imagePair) {
       var before =
           imagePair[constants.KEY__IMAGE_A_URL] + "-vs-" +
           imagePair[constants.KEY__IMAGE_B_URL];
       return before.replace(/[^\w\-]/g, "_") + ".png";
     }
 
   }
 );