Send batch requests when scheduling new commit builds

app_dart/lib/src/service/config.dart

@@ -143,6 +143,9 @@ class Config {
   /// Size of the shards to send to buildBucket when scheduling builds.
   int get schedulingShardSize => 5;
 
+  /// Batch size of builds to schedule in each swarming request.
+  int get batchSize => 5;
+
   /// Max retries when scheduling builds.
   static const RetryOptions schedulerRetry = RetryOptions(maxAttempts: 3);
 

app_dart/lib/src/service/scheduler.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:math';
 import 'dart:typed_data';
 
 import 'package:cocoon_service/src/service/build_status_provider.dart';
@@ -154,11 +155,24 @@ class Scheduler {
       log.severe('Failed to add commit ${commit.sha!}: $error');
     }
 
-    await luciBuildService.schedulePostsubmitBuilds(commit: commit, toBeScheduled: toBeScheduled);
-
+    await _batchScheduleBuilds(commit, toBeScheduled);
     await _uploadToBigQuery(commit);
   }
 
+  /// Schedule all builds in batch requests instead of a single request.
+  ///
+  /// Each batch request contains `kBatchSize` builds to be scheduled.
+  Future<void> _batchScheduleBuilds(Commit commit, List<Tuple<Target, Task, int>> toBeScheduled) async {
+    final List<Future> futures = <Future>[];
+    for (int i = 0; i < toBeScheduled.length; i += config.batchSize) {
+      futures.add(luciBuildService.schedulePostsubmitBuilds(
+        commit: commit,
+        toBeScheduled: toBeScheduled.sublist(i, min(i + config.batchSize, toBeScheduled.length)),
+      ));
+    }
+    await Future.wait<void>(futures);
+  }
+
   /// Return subset of [commits] not stored in Datastore.
   Future<List<Commit>> _getMissingCommits(List<Commit> commits) async {
     final List<Commit> newCommits = <Commit>[];

app_dart/test/service/scheduler_test.dart

@@ -135,6 +135,7 @@ void main() {
     });
 
     group('add commits', () {
+      final FakePubSub pubsub = FakePubSub();
       List<Commit> createCommitList(
         List<String> shas, {
         String repo = 'flutter',
@@ -255,6 +256,37 @@ void main() {
         final Iterable<Task> tasks = db.values.values.whereType<Task>();
         expect(tasks.singleWhere((Task task) => task.name == 'Linux A').status, Task.statusInProgress);
       });
+
+      test('schedules cocoon based targets - multiple batch requests', () async {
+        final MockBuildBucketClient mockBuildBucketClient = MockBuildBucketClient();
+        final FakeLuciBuildService luciBuildService = FakeLuciBuildService(
+          config,
+          buildbucket: mockBuildBucketClient,
+          gerritService: FakeGerritService(),
+          pubsub: pubsub,
+        );
+        when(mockBuildBucketClient.listBuilders(any)).thenAnswer((_) async {
+          return const ListBuildersResponse(builders: [
+            BuilderItem(id: BuilderId(bucket: 'prod', project: 'flutter', builder: 'Linux A')),
+            BuilderItem(id: BuilderId(bucket: 'prod', project: 'flutter', builder: 'Linux runIf')),
+          ]);
+        });
+        buildStatusService =
+            FakeBuildStatusService(commitStatuses: <CommitStatus>[CommitStatus(generateCommit(1), const <Stage>[])]);
+        config.batchSizeValue = 1;
+        scheduler = Scheduler(
+          cache: cache,
+          config: config,
+          buildStatusProvider: (_) => buildStatusService,
+          datastoreProvider: (DatastoreDB db) => DatastoreService(db, 2),
+          githubChecksService: GithubChecksService(config, githubChecksUtil: mockGithubChecksUtil),
+          httpClientProvider: () => httpClient,
+          luciBuildService: luciBuildService,
+        );
+
+        await scheduler.addCommits(createCommitList(<String>['1']));
+        expect(pubsub.messages.length, 2);
+      });
     });
 
     group('add pull request', () {

app_dart/test/src/datastore/fake_config.dart

@@ -56,6 +56,7 @@ class FakeConfig implements Config {
     this.supportedBranchesValue,
     this.luciBuildersValue,
     this.supportedReposValue,
+    this.batchSizeValue,
     FakeDatastoreDB? dbValue,
   }) : dbValue = dbValue ?? FakeDatastoreDB();
 
@@ -69,6 +70,7 @@ class FakeConfig implements Config {
   ServiceAccountInfo? deviceLabServiceAccountValue;
   int? maxTaskRetriesValue;
   int? maxLuciTaskRetriesValue;
+  int? batchSizeValue;
   FakeKeyHelper? keyHelperValue;
   String? oauthClientIdValue;
   String? githubOAuthTokenValue;
@@ -132,6 +134,9 @@ class FakeConfig implements Config {
   @override
   int get schedulingShardSize => 5;
 
+  @override
+  int get batchSize => batchSizeValue ?? 5;
+
   @override
   int get maxLuciTaskRetries => maxLuciTaskRetriesValue!;