map updates slowly with retry logic as tiles become available

lib/services/map_data_submodules/tiles_from_osm.dart

@@ -1,8 +1,13 @@
 import 'dart:math';
 import 'dart:io';
+import 'dart:async';
 import 'package:http/http.dart' as http;
+import 'package:flutter/foundation.dart';
 
-/// Fetches a tile from OSM, with in-memory retries/backoff.
+/// Global semaphore to limit simultaneous tile fetches
+final _tileFetchSemaphore = _SimpleSemaphore(4); // Max 4 concurrent
+
+/// Fetches a tile from OSM, with in-memory retries/backoff, and global concurrency limit.
 /// Returns tile image bytes, or throws on persistent failure.
 Future<List<int>> fetchOSMTile({
   required int z,
@@ -19,6 +24,7 @@ Future<List<int>> fetchOSMTile({
     10000 + random.nextInt(4000) - 2000
   ];
   while (true) {
+    await _tileFetchSemaphore.acquire();
     try {
       print('[fetchOSMTile] FETCH $z/$x/$y');
       attempt++;
@@ -40,6 +46,36 @@ Future<List<int>> fetchOSMTile({
       final delay = delays[attempt - 1].clamp(0, 60000);
       print("[fetchOSMTile] Attempt $attempt for $z/$x/$y failed: $e. Retrying in ${delay}ms.");
       await Future.delayed(Duration(milliseconds: delay));
+    } finally {
+      _tileFetchSemaphore.release();
     }
   }
 }
+
+/// Simple counting semaphore, suitable for single-thread Flutter concurrency
+class _SimpleSemaphore {
+  final int _max;
+  int _current = 0;
+  final List<VoidCallback> _queue = [];
+  _SimpleSemaphore(this._max);
+
+  Future<void> acquire() async {
+    if (_current < _max) {
+      _current++;
+      return;
+    } else {
+      final c = Completer<void>();
+      _queue.add(() => c.complete());
+      await c.future;
+    }
+  }
+
+  void release() {
+    if (_queue.isNotEmpty) {
+      final callback = _queue.removeAt(0);
+      callback();
+    } else {
+      _current--;
+    }
+  }
+}

lib/widgets/map_view.dart

@@ -86,6 +86,7 @@ class _MapViewState extends State<MapView> {
   late final MapController _controller;
   final MapDataProvider _mapDataProvider = MapDataProvider();
   final Debouncer _debounce = Debouncer(const Duration(milliseconds: 500));
+  Debouncer? _debounceTileLayerUpdate;
 
   StreamSubscription<Position>? _positionSub;
   LatLng? _currentLatLng;
@@ -111,6 +112,7 @@ class _MapViewState extends State<MapView> {
   @override
   void initState() {
     super.initState();
+    _debounceTileLayerUpdate = Debouncer(const Duration(milliseconds: 50),);
     // Kick off offline area loading as soon as map loads
     OfflineAreaService();
     _controller = widget.controller;
@@ -239,7 +241,9 @@ class _MapViewState extends State<MapView> {
           children: [
             TileLayer(
               tileProvider: TileProviderWithCache(
-                onTileCacheUpdated: () { if (mounted) setState(() {}); },
+                onTileCacheUpdated: () {
+                  if (_debounceTileLayerUpdate != null) _debounceTileLayerUpdate!(() { if (mounted) setState(() {}); });
+                },
               ),
               urlTemplate: 'unused-{z}-{x}-{y}',
               tileSize: 256,