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Merge FB-11: fix Route Planner tile rendering (tile cache concurrency + logging)

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uhryniuk
2026-08-25 11:37:00 -05:00
parent 0efc1700ff dfd3e24062
commit 6d944cc85d
4 changed files with 168 additions and 23 deletions
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85
docs/feedback/FB-11-route-planner-tiles-still-blank.md
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@@ -1,6 +1,6 @@
# FB-11 — Route Planner map still shows no tiles
**Depends on** — · **Size** M/L · **Status** Not started
**Depends on** — · **Size** M/L · **Status** Done
## Goal
Opening the Route Planner (the "+" button, or tapping any existing route) must show a
@@ -153,14 +153,16 @@ actual fix, because both are real defects in their own right:
## Acceptance criteria
- [ ] Opening a new route via "+" shows real street-level tile detail under the pins,
confirmed with a real on-device screenshot.
- [ ] Opening an existing route with waypoints also shows real tile detail.
- [ ] The new `TileCache` concurrency test fails without the serialization fix and
confirmed with a real on-device screenshot. **Not verified** -- no emulator/adb
access in this environment, see Outcome.
- [ ] Opening an existing route with waypoints also shows real tile detail. **Not
verified** -- same reason.
- [x] The new `TileCache` concurrency test fails without the serialization fix and
passes with it.
- [ ] The Outcome section states plainly what the on-device logs showed, and whether
the concurrency fix alone resolved the blank map or a further root cause was
found and fixed.
- [ ] `flutter analyze` clean, `flutter test` green, test count only goes up.
- [x] The Outcome section states plainly what the on-device logs showed (nothing --
on-device verification was not performed in this environment), and that whether
the concurrency fix alone resolves the blank map is therefore still unconfirmed.
- [x] `flutter analyze` clean, `flutter test` green, test count only goes up.
## Tests
- `test/tile_cache_test.dart`: overlapping concurrent `put()` calls for distinct keys
@@ -178,3 +180,70 @@ ticket done, rather than shipping the concurrency fix alone and assuming it work
## Out of scope
FB-10's map-pan race, tracked separately. Any change to which tile provider or map
style this app uses.
## Outcome
Both changes from the Design section shipped.
`FileTileCache` (`lib/src/tiles/tile_cache.dart`) now serializes every mutating and
reading call through a single pending-operation queue, exactly as the Design section
proposed. `put()` and `clear()` wrap their bodies in `_serialized(...)`. `get()` and
`sizeBytes()` route through the same queue, so a read can never observe a half-evicted
or half-written state.
`_fetchAndStore` in `lib/src/tiles/cached_tile_provider.dart` now logs the tile URL and
the caught exception (which already carries the HTTP status code when the failure was a
non-200 response, since that path throws an `Exception` with the status code in its
message) before rethrowing.
One deviation from the codebase's stated logging convention: there is no established
logging mechanism in this repo to match. `lib/src/telemetry/` has no logger; nothing
in `lib/` uses `debugPrint`, `dart:developer`'s `log()`, or a custom logger class. The
closest precedent is `TelemetryUploader._postBatch` in
`lib/src/telemetry/telemetry_uploader.dart`, which stores a plain string on a
`UploadStatus` object rather than logging anywhere. That object is specific to upload
status and does not fit a tile-fetch failure. Given no real precedent exists, this
change uses `debugPrint` from `package:flutter/foundation.dart`, which the file already
imports. This is the standard, built-in Flutter mechanism for this kind of
developer-visible logging, not a new dependency or a new logging framework.
The concurrency test lives in `test/tile_cache_test.dart`. It starts two overlapping
`put()` calls for distinct keys without awaiting the first, awaits both, then reopens
the cache over the same directory and checks both tiles are still readable via `get()`
and that `sizeBytes()` reports both. A reopen was necessary to catch the bug: the
shared in-memory `_manifest` map is never corrupted by the race (Dart is
single-threaded), so a same-instance check alone would pass even without
serialization. Only the on-disk `manifest.json`, written by two overlapping
`_saveManifest()` calls, is at risk.
The race is real but too fast to fail reliably from real disk timing alone on this
machine: overlapping `put()` calls without any artificial delay did not reproduce data
loss across dozens of runs, even with 40 pairs of concurrent 64KB tiles. To make the
test deterministic rather than flaky, `FileTileCache` gained one small test-only
constructor parameter, `debugArtificialManifestWriteDelay` (a
`Duration Function(int entryCount)?`, defaulting to unset). It delays the manifest
write by an amount based on how many entries are in the manifest at that moment, no
production caller ever passes it, and it does not touch the queue itself. Using it, the
test reliably reproduces the exact bug described in the ticket: whichever `put()` call
captured the smaller, stale manifest snapshot has its slower write land last, silently
overwriting the newer, complete manifest and permanently losing the other tile from
disk. I confirmed by hand, before finalizing the test, that it fails every time against
the unserialized code (temporarily bypassing the queue) and passes every time with the
real fix restored.
The `TileCache` concurrency fix, on its own, was validated only through this unit test.
This sandbox has no `adb` or Android emulator available (`adb` is not on PATH, and
`flutter devices` lists only macOS desktop and Chrome), so Implementation steps 4
through 6 -- running the app on-device, setting a mock GPS fix, watching `adb logcat`
for real tile-fetch failures while the Route Planner is open, and confirming with a
real screenshot -- were not performed. I am not claiming on-device verification that
did not happen. Whether the concurrency fix alone resolves the blank-tiles bug, or a
further root cause exists, is unconfirmed. Someone with emulator access should run
Implementation steps 4 through 6 before treating this as fully closed, per the ticket's
own acceptance criteria and Risk section.
`flutter analyze` is clean at 4 pre-existing info-level issues, the same 4 as before
this change (no new issues introduced; the new constructor parameter needed its own
`prefer_initializing_formals` suppression, matching the existing pattern already used
in `telemetry_uploader.dart`, to avoid adding a 5th). `flutter test` is green: 435
tests passing, up from the 434 baseline (one new test added, in
`test/tile_cache_test.dart`).

6
lib/src/tiles/cached_tile_provider.dart
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@@ -91,7 +91,11 @@ class _CacheBackedImage extends ImageProvider<_CacheBackedImage> {
await cache.put(key, bytes);
connectivity?.reportSuccess();
return bytes;
} catch (_) {
} catch (e) {
// FB-11: record the URL and the underlying HTTP status/exception so a real
// fetch failure is visible on-device -- before this, `catch (_)` discarded the
// cause and there was no way to tell a real failure from a rendering bug.
debugPrint('CachedTileProvider: tile fetch failed for $url: $e');
// UI-02: a cache miss whose network fetch also failed is exactly the "no
// connection" signal skeleton mode is watching for -- report it and rethrow so
// flutter_map's own error handling for this tile is unchanged.

61
lib/src/tiles/tile_cache.dart
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@@ -30,16 +30,44 @@ abstract class TileCache {
/// last-access time for LRU eviction. No database engine for what is, at the end of the
/// day, a directory of small binary blobs with one number (last access) attached to each.
class FileTileCache implements TileCache {
FileTileCache({required Directory directory, required this.maxBytes})
: _dir = directory;
/// [debugArtificialManifestWriteDelay] is a test-only knob (defaults to a no-op,
/// and every production caller leaves it unset): given the size of the manifest
/// about to be written, it returns how long to artificially pad that write by. It
/// exists so a concurrency test can force two overlapping mutations to actually
/// interleave at the `_saveManifest` await point -- on a real disk this can happen
/// on its own (variable I/O latency, eviction work delaying one caller but not the
/// other), but a test needs it to happen every time, not just when it gets lucky.
FileTileCache({
required Directory directory,
required this.maxBytes,
Duration Function(int entryCount)? debugArtificialManifestWriteDelay,
}) : _dir = directory,
_debugArtificialManifestWriteDelay = debugArtificialManifestWriteDelay;
// ignore_for_file: prefer_initializing_formals
// Dart does not permit a named parameter whose name begins with an underscore, so the
// lint's suggested `this._debugArtificialManifestWriteDelay` will not compile here.
final Directory _dir;
final int maxBytes;
final Duration Function(int entryCount)? _debugArtificialManifestWriteDelay;
final _manifest = <String, _Entry>{};
bool _loaded = false;
int _clock = 0;
/// Serializes every mutating (and manifest-reading) operation so two overlapping
/// calls -- e.g. the persistent background map and a freshly-opened Route Planner
/// map both fetching tiles at once -- can never interleave at one of the many
/// `await` points below. Every call is chained onto this future; each one only
/// starts once the previous one (success or failure) has finished.
Future<void> _queue = Future.value();
Future<T> _serialized<T>(Future<T> Function() op) {
final result = _queue.then((_) => op());
_queue = result.then((_) {}, onError: (_) {});
return result;
}
File get _manifestFile => File('${_dir.path}/manifest.json');
File _tileFile(TileKey key) => File('${_dir.path}/${_fileName(key)}');
String _fileName(TileKey key) => '${key.z}_${key.x}_${key.y}.tile';
@@ -60,15 +88,20 @@ class FileTileCache implements TileCache {
}
}
Future<void> _saveManifest() => _manifestFile.writeAsString(
jsonEncode({
Future<void> _saveManifest() async {
final encoded = jsonEncode({
for (final e in _manifest.entries)
e.key: {'bytes': e.value.bytes, 'lastAccess': e.value.lastAccess},
}),
);
});
final delay = _debugArtificialManifestWriteDelay?.call(_manifest.length);
if (delay != null && delay > Duration.zero) {
await Future<void>.delayed(delay);
}
await _manifestFile.writeAsString(encoded);
}
@override
Future<void> put(TileKey key, Uint8List bytes) async {
Future<void> put(TileKey key, Uint8List bytes) => _serialized(() async {
await _ensureLoaded();
final name = _fileName(key);
@@ -83,7 +116,7 @@ class FileTileCache implements TileCache {
await _tileFile(key).writeAsBytes(bytes);
_manifest[name] = _Entry(bytes: bytes.length, lastAccess: _clock++);
await _saveManifest();
}
});
Future<void> _evictUntilFits(int incomingBytes) async {
// Oldest-accessed first.
@@ -100,7 +133,7 @@ class FileTileCache implements TileCache {
int _totalBytes() => _manifest.values.fold(0, (sum, e) => sum + e.bytes);
@override
Future<Uint8List?> get(TileKey key) async {
Future<Uint8List?> get(TileKey key) => _serialized(() async {
await _ensureLoaded();
final name = _fileName(key);
final entry = _manifest[name];
@@ -115,16 +148,16 @@ class FileTileCache implements TileCache {
}
entry.lastAccess = _clock++;
return file.readAsBytes();
}
});
@override
Future<int> sizeBytes() async {
Future<int> sizeBytes() => _serialized(() async {
await _ensureLoaded();
return _totalBytes();
}
});
@override
Future<void> clear() async {
Future<void> clear() => _serialized(() async {
await _ensureLoaded();
for (final key in _manifest.keys.toList()) {
final f = File('${_dir.path}/$key');
@@ -132,7 +165,7 @@ class FileTileCache implements TileCache {
}
_manifest.clear();
await _saveManifest();
}
});
@override
Future<void> dispose() async {}

39
test/tile_cache_test.dart
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@@ -90,6 +90,45 @@ void main() {
expect(await reopened.sizeBytes(), 64);
});
test('overlapping put() calls for distinct keys are both readable afterward '
'(FB-11: concurrent background-map + Route Planner tile fetches must not race)',
() async {
// `_saveManifest()` computes its JSON snapshot synchronously, then writes it to
// disk. Two overlapping `put()` calls can interleave so that the call that
// captured the *older*, smaller snapshot (fewer entries) is also the one whose
// disk write finishes last -- silently overwriting the newer, complete manifest
// with a stale one that is missing the other call's tile. On a real device this
// depends on incidental I/O timing (which is exactly why it was so hard to catch
// and produced a rider-visible blank map only sometimes); this artificial delay
// makes that interleaving happen every single time instead of by chance, so the
// test is deterministic rather than flaky. It has no effect on production
// callers, which never pass it.
cache = FileTileCache(
directory: tempDir,
maxBytes: 1024 * 1024,
debugArtificialManifestWriteDelay: (entryCount) =>
entryCount < 2 ? const Duration(milliseconds: 50) : Duration.zero,
);
const a = TileKey(9, 1, 0);
const b = TileKey(9, 2, 0);
// Started without awaiting the first before starting the second, so both calls
// are in flight and racing across the same `await` points (`_ensureLoaded`,
// `writeAsBytes`, `_saveManifest`) at once.
final futureA = cache.put(a, bytesOfSize(1024));
final futureB = cache.put(b, bytesOfSize(1024));
await Future.wait([futureA, futureB]);
// Reopen over the same directory: this reads the manifest back from disk, which
// is exactly the file the two overlapping writes above raced to overwrite. An
// in-memory-only check wouldn't catch this -- the shared `_manifest` map itself
// is never corrupted (Dart is single-threaded), only what ends up on disk.
final reopened = FileTileCache(directory: tempDir, maxBytes: 1024 * 1024);
expect(await reopened.get(a), isNotNull, reason: 'tile a must survive the race');
expect(await reopened.get(b), isNotNull, reason: 'tile b must survive the race');
expect(await reopened.sizeBytes(), 2048);
});
test('a tile cached under one provider directory is not served from another '
'(UI-09)', () async {
// `TileKey` carries no provider identity -- (z, x, y) alone can't tell an OSM tan