Better caching support for async tile images about ol2 HOT 4 CLOSED

Hi, just for me to understand:

1. After a tile has been served, an identical /GetMap request is triggered
2. While the /GetMap request for tile 1 is processed on the server, an identical request is triggered

Are you saying that OpenLayers triggers a 2nd request for the same tile on its own, or just that if the user requests the same map extent again, a new request is sent? If the former, then we have a bug somewhere in OpenLayers. If the latter, then I don't expect any efforts in client-side cache management of asynchronous requests, since the only layer type that currently uses asynchronous tile loading is Layer.ArcIMS, and ArcIMS was deprecated by ESRI.

The only future use of asynchronous tile requests in OpenLayers I can think of is offline storage, which might help you as well. Other than that, your solution for problem 1 sounds reasonable, and for problem 2 you could have a cache of pending requests by bounds and reassign the callback if a request for the same bounds is pending.

Please close this ticket if the information provided here was helpful. If, on the other hand, your proprietary map service is a commonly used one, provide more information about that service and turn this ticket into a feature request for creating a layer type for that service. This feature could then become at least an add-in.

from ol2.

thanks for the quick reply!

seems that OpenLayers triggers the request from time to time, I will try to track that down and open a new ticket for the exact cause (maybe the fault is on my side by making bad use of the API).
Anyhow I like to safeguard my layer against unneeded requests, so that it behaves gracefully even in non-optimal configurations.
Just for clarification: by "reassign the callback if a request for the same bounds is pending" you mean something like:

 //getURLasync layer of subclassed grid method, `tileCache` and `pendingRequests` are object properties.
 getURLasync: function (bounds, scope, prop, callback) {
      bounds = this.adjustBounds(bounds);
      var requestParams = this.getMyMapRequestParams(bounds, this.map.getSize());
      var reqQueryString = $.param(requestParams);
      var self = this;

      //check if there is a pending request for the same extent
      //and reassign the callback if necessary
      if (this.pendingRequests[reqQueryString]) {
          callback = self.pendingRequests[reqQueryString];
      }

      //check if there is already a completed tile request for the same extent
      else if (self.tileCache[reqQueryString]) {
          scope[prop] = self.tileCache[reqQueryString];
          callback.apply(scope);
      }

      //issue a new get request
      else {
          self.pendingRequests[reqQueryString] = callback;
          jQuery.get(this.methodPath, requestParams, function (response) {
              var mapData = self.parseMapResponse(response);
              scope[prop] = mapData.url;
              callback.apply(scope);
              //fill tilecache object
              self.tileCache[reqQueryString] = mapData.url;
              //delete pending request
              delete self.pendingRequests[reqQueryString]; 
          });
      }
  }

from ol2.

Yes, the above looks like what I had in mind.

from ol2.

Thanks for the suggestions, finally I found the source of error in another code part.

from ol2.