Isolate-based access to the SDK index (but not used yet).

app/lib/search/sdk_mem_index.dart

@@ -2,6 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:async';
 import 'dart:math';
 
 import 'package:gcloud/service_scope.dart' as ss;
@@ -66,8 +67,18 @@ Future<SdkMemIndex?> createSdkMemIndex() async {
   }
 }
 
+/// Defines the general interface for the SDK index.
+// ignore: one_member_abstracts
+abstract class SdkIndex {
+  FutureOr<List<SdkLibraryHit>> search(
+    String query, {
+    int? limit,
+    bool skipFlutter = false,
+  });
+}
+
 /// In-memory index for SDK library search queries.
-class SdkMemIndex {
+class SdkMemIndex implements SdkIndex {
   final _libraries = <String, _Library>{};
   final Map<String, double> _apiPageDirWeights;
 
@@ -126,6 +137,7 @@ class SdkMemIndex {
     }
   }
 
+  @override
   List<SdkLibraryHit> search(
     String query, {
     int? limit,

app/lib/service/entrypoint/_isolate.dart

@@ -8,6 +8,8 @@ import 'dart:isolate';
 
 import 'package:collection/collection.dart';
 import 'package:logging/logging.dart';
+import 'package:pub_dev/service/entrypoint/tools.dart';
+import 'package:pub_dev/shared/monitoring.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 import '../services.dart';
@@ -325,3 +327,31 @@ Future<void> _wrapper(List args) async {
     timer.cancel();
   }
 }
+
+/// Run [fn] inside the isolate, using message passing from the control isolate.
+Future<void> runIsolateFunctions({
+  required Object? message,
+  required Logger logger,
+  required Future<ReplyMessage> Function(Object payload) fn,
+}) async {
+  final requestReceivePort = ReceivePort();
+  final entryMessage = Message.fromObject(message) as EntryMessage;
+
+  final subs = requestReceivePort.listen((e) async {
+    try {
+      final msg = Message.fromObject(e) as RequestMessage;
+      final reply = await fn(msg.payload);
+      msg.replyPort.send(reply.encodeAsJson());
+    } catch (e, st) {
+      logger.pubNoticeShout(
+          'isolate-message-error', 'Error processing message: $e', e, st);
+    }
+  });
+  entryMessage.protocolSendPort.send(
+    ReadyMessage(requestSendPort: requestReceivePort.sendPort).encodeAsJson(),
+  );
+
+  await waitForProcessSignalTermination();
+  requestReceivePort.close();
+  await subs.cancel();
+}

app/lib/service/entrypoint/sdk_isolate_index.dart

@@ -0,0 +1,81 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:gcloud/service_scope.dart';
+import 'package:logging/logging.dart';
+import 'package:pub_dev/service/entrypoint/logging.dart';
+import 'package:pub_dev/service/services.dart';
+import 'package:pub_dev/shared/env_config.dart';
+import 'package:pub_dev/shared/logging.dart';
+
+import '../../../service/entrypoint/_isolate.dart';
+
+import '../../search/sdk_mem_index.dart';
+import '../../search/search_service.dart';
+
+final _logger = Logger('sdk_search_index');
+
+/// Entry point for the SDK search index isolate.
+Future<void> main(List<String> args, var message) async {
+  final timer = Timer.periodic(Duration(milliseconds: 250), (_) {});
+
+  final ServicesWrapperFn servicesWrapperFn;
+  if (envConfig.isRunningInAppengine) {
+    servicesWrapperFn = withServices;
+    setupAppEngineLogging();
+  } else {
+    servicesWrapperFn = (fn) => withFakeServices(fn: fn);
+    setupDebugEnvBasedLogging();
+  }
+
+  await fork(() async {
+    await servicesWrapperFn(() async {
+      final sdkMemIndex = await createSdkMemIndex();
+      await runIsolateFunctions(
+          message: message,
+          logger: _logger,
+          fn: (payload) async {
+            final args = payload as List;
+            final rs = sdkMemIndex!.search(
+              args[0] as String,
+              limit: args[1] as int?,
+              skipFlutter: args[2] as bool,
+            );
+            return ReplyMessage.result(rs.map((e) => e.toJson()).toList());
+          });
+    });
+  });
+
+  timer.cancel();
+}
+
+/// Implementation of [SdkMemIndex] that uses [RequestMessage]s to send requests
+/// across isolate boundaries. The instance should be registered inside the
+/// `frontend` isolate, and it calls the `sdk-index` isolate as a delegate.
+class SdkIsolateIndex implements SdkIndex {
+  final IsolateRunner _runner;
+  SdkIsolateIndex(this._runner);
+
+  @override
+  Future<List<SdkLibraryHit>> search(
+    String query, {
+    int? limit,
+    bool skipFlutter = false,
+  }) async {
+    try {
+      final rs = await _runner.sendRequest(
+        [query, limit, skipFlutter],
+        timeout: Duration(seconds: 2),
+      );
+      return (rs as List)
+          .map((v) => SdkLibraryHit.fromJson(v as Map<String, dynamic>))
+          .toList();
+    } catch (e, st) {
+      _logger.warning('Failed to search SDK index.', e, st);
+      return <SdkLibraryHit>[];
+    }
+  }
+}

app/lib/service/entrypoint/search_index.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'dart:convert';
-import 'dart:isolate';
 
 import 'package:gcloud/service_scope.dart';
 import 'package:logging/logging.dart';
@@ -39,43 +38,24 @@ Future<void> main(List<String> args, var message) async {
       registerSdkMemIndex(await createSdkMemIndex());
       await indexUpdater.init();
 
-      final requestReceivePort = ReceivePort();
-      final entryMessage = Message.fromObject(message) as EntryMessage;
-
-      final subs = requestReceivePort.listen((e) async {
-        try {
-          final msg = Message.fromObject(e) as RequestMessage;
-          final payload = msg.payload;
+      await runIsolateFunctions(
+        message: message,
+        logger: _logger,
+        fn: (payload) async {
           if (payload is String && payload == 'info') {
             final info = await searchIndex.indexInfo();
-            msg.replyPort
-                .send(ReplyMessage.result(info.toJson()).encodeAsJson());
-            return;
+            return ReplyMessage.result(info.toJson());
           } else if (payload is String) {
             final q = ServiceSearchQuery.fromServiceUrl(Uri.parse(payload));
             final rs = await searchIndex.search(q);
-            msg.replyPort.send(
-                ReplyMessage.result(json.encode(rs.toJson())).encodeAsJson());
-            return;
+            return ReplyMessage.result(json.encode(rs.toJson()));
           } else {
             _logger.pubNoticeShout(
-                'unknown-isolate-message', 'Unrecognized payload: $msg');
-            msg.replyPort.send(ReplyMessage.error('Unrecognized payload: $msg')
-                .encodeAsJson());
+                'unknown-isolate-message', 'Unrecognized payload: $payload');
+            return ReplyMessage.error('Unrecognized payload: $payload');
           }
-        } catch (e, st) {
-          _logger.pubNoticeShout(
-              'isolate-message-error', 'Error processing message: $e', e, st);
-        }
-      });
-      entryMessage.protocolSendPort.send(
-        ReadyMessage(requestSendPort: requestReceivePort.sendPort)
-            .encodeAsJson(),
+        },
       );
-
-      await Completer().future;
-      requestReceivePort.close();
-      await subs.cancel();
     });
   });
 

app/test/service/entrypoint/sdk_isolate_index_test.dart

@@ -0,0 +1,44 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:logging/logging.dart';
+import 'package:pub_dev/service/entrypoint/_isolate.dart';
+import 'package:pub_dev/service/entrypoint/sdk_isolate_index.dart';
+import 'package:test/test.dart';
+
+final _logger = Logger('sdk_isolate_index_test');
+
+void main() {
+  group('SDK index inside an isolate', () {
+    final indexRunner = IsolateRunner.uri(
+      kind: 'index',
+      logger: _logger,
+      spawnUri: Uri.parse(
+          'package:pub_dev/service/entrypoint/sdk_isolate_index.dart'),
+    );
+
+    tearDownAll(() async {
+      await indexRunner.close();
+    });
+
+    test('start and work with index', () async {
+      await indexRunner.start(1);
+
+      final sdkIndex = SdkIsolateIndex(indexRunner);
+
+      final rs = await sdkIndex.search('json');
+      expect(rs.map((e) => e.toJson()).toList(), [
+        {
+          'sdk': 'dart',
+          'library': 'dart:convert',
+          'description': isNotNull,
+          'url': 'https://api.dart.dev/stable/latest/dart-convert/',
+          'score': isNotNull,
+          'apiPages': isNotEmpty,
+        },
+        isA<Map>(), // second hit from `package:flutter_driver`
+      ]);
+    }, timeout: Timeout(Duration(minutes: 5)));
+  });
+}

app/test/shared/timer_import_test.dart

@@ -44,6 +44,9 @@ void main() {
     // Uses timer to prevent GC compaction.
     'lib/service/entrypoint/search_index.dart',
 
+    // Uses timer to prevent GC compaction.
+    'lib/service/entrypoint/sdk_isolate_index.dart',
+
     // Uses timer to timeout GlobalLock claim acquisition.
     'lib/tool/neat_task/pub_dev_tasks.dart',