[ios][android][core] Added change log entries and more code comments

platform/android/CHANGELOG.md

@@ -4,6 +4,9 @@ Mapbox welcomes participation and contributions from everyone.  If you'd like to
 
 ## master
 
+### Bug fixes
+ - Fixed the rendering bug caused by redundant pending requests for already requested images [#15864](https://github.com/mapbox/mapbox-gl-native/pull/15864)
+
 ### Performance improvements
  - Enable incremental vacuum for the offline database in order to make data removal requests faster and to avoid the excessive disk space usage (creating a backup file on VACUUM call) [#15837](https://github.com/mapbox/mapbox-gl-native/pull/15837)
 

platform/ios/CHANGELOG.md

@@ -6,7 +6,8 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 
 ### Other changes
 
-* Coalesce requests to the client for the same missing image ([#15778](https://github.com/mapbox/mapbox-gl-native/pull/15778))
+### Bug fixes
+* Fixed the rendering bug caused by redundant pending requests for already requested images [#15864](https://github.com/mapbox/mapbox-gl-native/pull/15864)
 * Enable incremental vacuum for the offline database in order to make data removal requests faster and to avoid the excessive disk space usage (creating a backup file on VACUUM call). ([#15837](https://github.com/mapbox/mapbox-gl-native/pull/15837))
 
 ## 5.5.0

src/mbgl/renderer/image_manager.cpp

@@ -190,6 +190,7 @@ void ImageManager::checkMissingAndNotify(ImageRequestor& requestor, const ImageR
             auto existingRequestorsIt = requestedImages.find(missingImage);
             if (existingRequestorsIt != requestedImages.end()) { // Already asked client about this image.
                 std::set<ImageRequestor*>& existingRequestors = existingRequestorsIt->second;
+                // existingRequestors is empty if all the previous requestors are deleted.
                 if (!existingRequestors.empty() &&
                     (*existingRequestors.begin())
                         ->hasPendingRequest(missingImage)) { // Still waiting for the client response for this image.
@@ -200,6 +201,8 @@ void ImageManager::checkMissingAndNotify(ImageRequestor& requestor, const ImageR
                 // The request for this image has been already delivered
                 // to the client, so we do not treat it as pending.
                 existingRequestors.emplace(requestorPtr);
+                // TODO: we could `continue;` here, but we need to call `observer->onStyleImageMissing`,
+                // so that rendering is re-launched from the handler at Map::Impl.
             } else {
                 requestedImages[missingImage].emplace(requestorPtr);
                 requestor.addPendingRequest(missingImage);