From d5481a626b5c274303892e81148ea1a3c6e06277 Mon Sep 17 00:00:00 2001
From: Liam Appelbe <liama@google.com>
Date: Tue, 8 Apr 2025 15:39:42 +1000
Subject: [PATCH 1/4] wip

---
 pkgs/coverage/lib/src/collect.dart            |   4 +-
 .../lib/src/isolate_paused_listener.dart      | 151 ++++++++++--------
 pkgs/coverage/test/collect_coverage_test.dart |  23 +--
 pkgs/coverage/test/run_and_collect_test.dart  |  18 +--
 .../test/test_files/test_app_isolate.dart     |   1 +
 5 files changed, 105 insertions(+), 92 deletions(-)

diff --git a/pkgs/coverage/lib/src/collect.dart b/pkgs/coverage/lib/src/collect.dart
index 76227bac9..a26c67cec 100644
--- a/pkgs/coverage/lib/src/collect.dart
+++ b/pkgs/coverage/lib/src/collect.dart
@@ -179,9 +179,10 @@ Future<Map<String, dynamic>> _getAllCoverage(
     await IsolatePausedListener(service,
             (IsolateRef isolateRef, bool isLastIsolateInGroup) async {
       if (isLastIsolateInGroup) {
+        logfile.writeln("    Collecting $isolateRef");
         await collectIsolate(isolateRef);
       }
-    }, stderr.writeln)
+    }, logfile.writeln)
         .waitUntilAllExited();
   } else {
     for (final isolateRef in await getAllIsolates(service)) {
@@ -202,6 +203,7 @@ Future _resumeIsolates(VmService service) async {
     futures.add(Future.sync(() async {
       final isolate = await service.getIsolate(isolateRef.id!);
       if (isolate.pauseEvent!.kind != EventKind.kResume) {
+        logfile.writeln("        Resuming0: ${isolateRef}");
         await service.resume(isolateRef.id!);
       }
     }));
diff --git a/pkgs/coverage/lib/src/isolate_paused_listener.dart b/pkgs/coverage/lib/src/isolate_paused_listener.dart
index 6f538a4e3..e4bf94018 100644
--- a/pkgs/coverage/lib/src/isolate_paused_listener.dart
+++ b/pkgs/coverage/lib/src/isolate_paused_listener.dart
@@ -4,12 +4,15 @@
 
 import 'dart:async';
 import 'dart:collection';
+import 'dart:io';
 
 import 'package:meta/meta.dart';
 import 'package:vm_service/vm_service.dart';
 
 import 'util.dart';
 
+final logfile = File('log_${DateTime.timestamp().millisecondsSinceEpoch}.txt').openWrite();
+
 typedef SyncIsolateCallback = void Function(IsolateRef isolate);
 typedef AsyncIsolateCallback = Future<void> Function(IsolateRef isolate);
 typedef AsyncIsolatePausedCallback = Future<void> Function(
@@ -28,30 +31,47 @@ class IsolatePausedListener {
 
   final _isolateGroups = <String, IsolateGroupState>{};
 
-  int _numNonMainIsolates = 0;
-  final _allNonMainIsolatesExited = Completer<void>();
-  bool _finished = false;
+  int _numIsolates = 0;
+  bool _finishedListening = false;
 
   IsolateRef? _mainIsolate;
-  final _mainIsolatePaused = Completer<bool>();
+  bool _hasMainIsolate = false;
+
+  // Completes when either:
+  // - there is a main isolate, and it is paused or exited
+  // - there is no main isolate, and all isolates have exited
+  final _mainIsolatePausedOrAllIsolatesExited = Completer<void>();
 
   /// Starts listening and returns a future that completes when all isolates
   /// have exited.
   Future<void> waitUntilAllExited() async {
     await listenToIsolateLifecycleEvents(_service, _onStart, _onPause, _onExit);
 
-    await _allNonMainIsolatesExited.future;
-
-    // Resume the main isolate.
-    try {
-      if (_mainIsolate != null) {
-        if (await _mainIsolatePaused.future) {
-          await _runCallbackAndResume(
-              _mainIsolate!, !_getGroup(_mainIsolate!).collected);
+    logfile.writeln("_mainIsolatePausedOrAllIsolatesExited BEFORE");
+    await _mainIsolatePausedOrAllIsolatesExited.future;
+    logfile.writeln("_mainIsolatePausedOrAllIsolatesExited AFTER");
+    _finishedListening = true;
+
+    // Collect all remaining uncollected groups.
+    logfile.writeln("Creating collection tasks");
+    final collectionTasks = <Future<void>>[];
+    for (final group in _isolateGroups.values) {
+      if (!group.collected) {
+        group.collected = true;
+        final iso = group.paused.firstOrNull ?? group.running.firstOrNull;
+        if (iso != null) {
+          collectionTasks.add(_onIsolatePaused(iso, true));
         }
       }
-    } finally {
-      _finished = true;
+    }
+    logfile.writeln("Awaiting collection tasks");
+    await Future.wait(collectionTasks);
+    logfile.writeln("Collection tasks done");
+
+    // Resume the main isolate.
+    if (_mainIsolate != null) {
+      logfile.writeln("        Resuming1: ${_mainIsolate}");
+      await _service.resume(_mainIsolate!.id!);
     }
   }
 
@@ -59,70 +79,55 @@ class IsolatePausedListener {
       _isolateGroups[isolateRef.isolateGroupId!] ??= IsolateGroupState();
 
   void _onStart(IsolateRef isolateRef) {
-    if (_finished) return;
+    logfile.writeln("    _onStart: $isolateRef");
+    if (_finishedListening) return;
     final group = _getGroup(isolateRef);
-    group.start(isolateRef.id!);
-    if (_mainIsolate == null && _isMainIsolate(isolateRef)) {
+    group.start(isolateRef);
+    ++_numIsolates;
+    if (!_hasMainIsolate && _isMainIsolate(isolateRef)) {
       _mainIsolate = isolateRef;
-    } else {
-      ++_numNonMainIsolates;
+      _hasMainIsolate = true;
     }
   }
 
   Future<void> _onPause(IsolateRef isolateRef) async {
-    if (_finished) return;
+    logfile.writeln("    _onPause: $isolateRef");
+    if (_finishedListening) return;
     final group = _getGroup(isolateRef);
-    group.pause(isolateRef.id!);
+    group.pause(isolateRef);
     if (isolateRef.id! == _mainIsolate?.id) {
-      _mainIsolatePaused.complete(true);
-
-      // If the main isolate is the only isolate, then _allNonMainIsolatesExited
-      // will never be completed. So check that case here.
-      _checkCompleted();
+      _mainIsolatePausedOrAllIsolatesExited.safeComplete();
     } else {
-      await _runCallbackAndResume(isolateRef, group.noRunningIsolates);
-    }
-  }
-
-  Future<void> _runCallbackAndResume(
-      IsolateRef isolateRef, bool isLastIsolateInGroup) async {
-    if (isLastIsolateInGroup) {
-      _getGroup(isolateRef).collected = true;
-    }
-    try {
-      await _onIsolatePaused(isolateRef, isLastIsolateInGroup);
-    } finally {
-      await _service.resume(isolateRef.id!);
+      final isLastIsolateInGroup = group.noRunningIsolates;
+      if (isLastIsolateInGroup) {
+        _getGroup(isolateRef).collected = true;
+      }
+      try {
+        await _onIsolatePaused(isolateRef, isLastIsolateInGroup);
+      } finally {
+        logfile.writeln("        Resuming2: ${isolateRef}");
+        group.exit(isolateRef);
+        await _service.resume(isolateRef.id!);
+      }
     }
   }
 
   void _onExit(IsolateRef isolateRef) {
-    if (_finished) return;
+    logfile.writeln("    _onExit: $isolateRef");
+    if (_finishedListening) return;
     final group = _getGroup(isolateRef);
-    group.exit(isolateRef.id!);
+    group.exit(isolateRef);
+    --_numIsolates;
     if (group.noLiveIsolates && !group.collected) {
       _log('ERROR: An isolate exited without pausing, causing '
           'coverage data to be lost for group ${isolateRef.isolateGroupId!}.');
     }
     if (isolateRef.id! == _mainIsolate?.id) {
-      if (!_mainIsolatePaused.isCompleted) {
-        // Main isolate exited without pausing.
-        _mainIsolatePaused.complete(false);
-      }
-    } else {
-      --_numNonMainIsolates;
-      _checkCompleted();
-    }
-  }
-
-  bool get _mainRunning =>
-      _mainIsolate != null && !_mainIsolatePaused.isCompleted;
-
-  void _checkCompleted() {
-    if (_numNonMainIsolates == 0 &&
-        !_mainRunning &&
-        !_allNonMainIsolatesExited.isCompleted) {
-      _allNonMainIsolatesExited.complete();
+      // Main isolate exited without pausing.
+      _mainIsolate = null;
+      _mainIsolatePausedOrAllIsolatesExited.safeComplete();
+    } else if (!_hasMainIsolate && _numIsolates == 0) {
+      _mainIsolatePausedOrAllIsolatesExited.safeComplete();
     }
   }
 
@@ -139,6 +144,12 @@ class IsolatePausedListener {
   }
 }
 
+extension on Completer {
+  void safeComplete() {
+    if (!isCompleted) complete();
+  }
+}
+
 /// Listens to isolate start and pause events, and backfills events for isolates
 /// that existed before listening started.
 ///
@@ -220,30 +231,30 @@ Future<void> listenToIsolateLifecycleEvents(
 class IsolateGroupState {
   // IDs of the isolates running in this group.
   @visibleForTesting
-  final running = <String>{};
+  final running = <IsolateRef>{};
 
   // IDs of the isolates paused just before exiting in this group.
   @visibleForTesting
-  final paused = <String>{};
+  final paused = <IsolateRef>{};
 
   bool collected = false;
 
   bool get noRunningIsolates => running.isEmpty;
   bool get noLiveIsolates => running.isEmpty && paused.isEmpty;
 
-  void start(String id) {
-    paused.remove(id);
-    running.add(id);
+  void start(IsolateRef iso) {
+    paused.remove(iso);
+    running.add(iso);
   }
 
-  void pause(String id) {
-    running.remove(id);
-    paused.add(id);
+  void pause(IsolateRef iso) {
+    running.remove(iso);
+    paused.add(iso);
   }
 
-  void exit(String id) {
-    running.remove(id);
-    paused.remove(id);
+  void exit(IsolateRef iso) {
+    running.remove(iso);
+    paused.remove(iso);
   }
 
   @override
diff --git a/pkgs/coverage/test/collect_coverage_test.dart b/pkgs/coverage/test/collect_coverage_test.dart
index 7262757be..476fee1c2 100644
--- a/pkgs/coverage/test/collect_coverage_test.dart
+++ b/pkgs/coverage/test/collect_coverage_test.dart
@@ -133,24 +133,25 @@ void main() {
       39: 1,
       41: 1,
       42: 4,
-      43: 1,
-      44: 3,
-      45: 1,
-      48: 1,
+      43: 2,
+      44: 1,
+      45: 3,
+      46: 1,
       49: 1,
-      51: 1,
-      54: 1,
+      50: 1,
+      52: 1,
       55: 1,
       56: 1,
-      59: 1,
+      57: 1,
       60: 1,
-      62: 1,
+      61: 1,
       63: 1,
       64: 1,
-      66: 1,
+      65: 1,
       67: 1,
       68: 1,
-      71: 3,
+      69: 1,
+      72: 3,
     };
     expect(isolateFile?.lineHits, expectedHits);
     expect(isolateFile?.funcHits, {11: 1, 19: 1, 23: 1, 28: 1, 38: 1});
@@ -174,7 +175,7 @@ void main() {
         32: 0,
         38: 1,
         42: 1,
-        71: 1,
+        72: 1,
       },
     );
   });
diff --git a/pkgs/coverage/test/run_and_collect_test.dart b/pkgs/coverage/test/run_and_collect_test.dart
index e371f9000..9c9c943f8 100644
--- a/pkgs/coverage/test/run_and_collect_test.dart
+++ b/pkgs/coverage/test/run_and_collect_test.dart
@@ -84,10 +84,7 @@ void checkIgnoredLinesInFilesCache(
   expect(ignoredLinesInFilesCache[packageUtilKey], isEmpty);
   expect(ignoredLinesInFilesCache[testAppKey], null /* means whole file */);
   expect(ignoredLinesInFilesCache[testAppIsolateKey], [
-    [51, 51],
-    [53, 57],
-    [62, 65],
-    [66, 72]
+    [52, 52], [54, 58], [63, 66], [67, 73]
   ]);
 }
 
@@ -112,13 +109,14 @@ void checkHitmap(Map<String, HitMap> hitMap) {
     39: 1,
     41: 1,
     42: 4,
-    43: 1,
-    44: 3,
-    45: 1,
-    48: 1,
+    43: 2,
+    44: 1,
+    45: 3,
+    46: 1,
     49: 1,
-    59: 1,
-    60: 1
+    50: 1,
+    60: 1,
+    61: 1
   };
 
   expect(actualLineHits, expectedLineHits);
diff --git a/pkgs/coverage/test/test_files/test_app_isolate.dart b/pkgs/coverage/test/test_files/test_app_isolate.dart
index 8bbc6be31..4a2695d8e 100644
--- a/pkgs/coverage/test/test_files/test_app_isolate.dart
+++ b/pkgs/coverage/test/test_files/test_app_isolate.dart
@@ -40,6 +40,7 @@ void isolateTask(List threeThings) async {
 
   fooSync(answer);
   unawaited(fooAsync(answer).then((_) {
+    final keepAlive = RawReceivePort()..keepIsolateAlive = true;
     final port = threeThings.first as SendPort;
     final sum = (threeThings[1] as int) + (threeThings[2] as int);
     port.send(sum);

From e9b97c0ba7eb0a9ea0ad47e5134058de87afdac6 Mon Sep 17 00:00:00 2001
From: Liam Appelbe <liama@google.com>
Date: Wed, 9 Apr 2025 13:19:18 +1000
Subject: [PATCH 2/4] Test and clean up

---
 pkgs/coverage/lib/src/collect.dart            |   4 +-
 .../lib/src/isolate_paused_listener.dart      |  12 --
 .../test/isolate_paused_listener_test.dart    | 170 +++++++++++-------
 pkgs/coverage/test/run_and_collect_test.dart  |   5 +-
 4 files changed, 109 insertions(+), 82 deletions(-)

diff --git a/pkgs/coverage/lib/src/collect.dart b/pkgs/coverage/lib/src/collect.dart
index a26c67cec..76227bac9 100644
--- a/pkgs/coverage/lib/src/collect.dart
+++ b/pkgs/coverage/lib/src/collect.dart
@@ -179,10 +179,9 @@ Future<Map<String, dynamic>> _getAllCoverage(
     await IsolatePausedListener(service,
             (IsolateRef isolateRef, bool isLastIsolateInGroup) async {
       if (isLastIsolateInGroup) {
-        logfile.writeln("    Collecting $isolateRef");
         await collectIsolate(isolateRef);
       }
-    }, logfile.writeln)
+    }, stderr.writeln)
         .waitUntilAllExited();
   } else {
     for (final isolateRef in await getAllIsolates(service)) {
@@ -203,7 +202,6 @@ Future _resumeIsolates(VmService service) async {
     futures.add(Future.sync(() async {
       final isolate = await service.getIsolate(isolateRef.id!);
       if (isolate.pauseEvent!.kind != EventKind.kResume) {
-        logfile.writeln("        Resuming0: ${isolateRef}");
         await service.resume(isolateRef.id!);
       }
     }));
diff --git a/pkgs/coverage/lib/src/isolate_paused_listener.dart b/pkgs/coverage/lib/src/isolate_paused_listener.dart
index e4bf94018..5a7591855 100644
--- a/pkgs/coverage/lib/src/isolate_paused_listener.dart
+++ b/pkgs/coverage/lib/src/isolate_paused_listener.dart
@@ -11,8 +11,6 @@ import 'package:vm_service/vm_service.dart';
 
 import 'util.dart';
 
-final logfile = File('log_${DateTime.timestamp().millisecondsSinceEpoch}.txt').openWrite();
-
 typedef SyncIsolateCallback = void Function(IsolateRef isolate);
 typedef AsyncIsolateCallback = Future<void> Function(IsolateRef isolate);
 typedef AsyncIsolatePausedCallback = Future<void> Function(
@@ -47,13 +45,10 @@ class IsolatePausedListener {
   Future<void> waitUntilAllExited() async {
     await listenToIsolateLifecycleEvents(_service, _onStart, _onPause, _onExit);
 
-    logfile.writeln("_mainIsolatePausedOrAllIsolatesExited BEFORE");
     await _mainIsolatePausedOrAllIsolatesExited.future;
-    logfile.writeln("_mainIsolatePausedOrAllIsolatesExited AFTER");
     _finishedListening = true;
 
     // Collect all remaining uncollected groups.
-    logfile.writeln("Creating collection tasks");
     final collectionTasks = <Future<void>>[];
     for (final group in _isolateGroups.values) {
       if (!group.collected) {
@@ -64,13 +59,10 @@ class IsolatePausedListener {
         }
       }
     }
-    logfile.writeln("Awaiting collection tasks");
     await Future.wait(collectionTasks);
-    logfile.writeln("Collection tasks done");
 
     // Resume the main isolate.
     if (_mainIsolate != null) {
-      logfile.writeln("        Resuming1: ${_mainIsolate}");
       await _service.resume(_mainIsolate!.id!);
     }
   }
@@ -79,7 +71,6 @@ class IsolatePausedListener {
       _isolateGroups[isolateRef.isolateGroupId!] ??= IsolateGroupState();
 
   void _onStart(IsolateRef isolateRef) {
-    logfile.writeln("    _onStart: $isolateRef");
     if (_finishedListening) return;
     final group = _getGroup(isolateRef);
     group.start(isolateRef);
@@ -91,7 +82,6 @@ class IsolatePausedListener {
   }
 
   Future<void> _onPause(IsolateRef isolateRef) async {
-    logfile.writeln("    _onPause: $isolateRef");
     if (_finishedListening) return;
     final group = _getGroup(isolateRef);
     group.pause(isolateRef);
@@ -105,7 +95,6 @@ class IsolatePausedListener {
       try {
         await _onIsolatePaused(isolateRef, isLastIsolateInGroup);
       } finally {
-        logfile.writeln("        Resuming2: ${isolateRef}");
         group.exit(isolateRef);
         await _service.resume(isolateRef.id!);
       }
@@ -113,7 +102,6 @@ class IsolatePausedListener {
   }
 
   void _onExit(IsolateRef isolateRef) {
-    logfile.writeln("    _onExit: $isolateRef");
     if (_finishedListening) return;
     final group = _getGroup(isolateRef);
     group.exit(isolateRef);
diff --git a/pkgs/coverage/test/isolate_paused_listener_test.dart b/pkgs/coverage/test/isolate_paused_listener_test.dart
index b6016ce14..dc77408ef 100644
--- a/pkgs/coverage/test/isolate_paused_listener_test.dart
+++ b/pkgs/coverage/test/isolate_paused_listener_test.dart
@@ -129,73 +129,78 @@ void main() {
     expect(group.noRunningIsolates, isTrue);
     expect(group.noLiveIsolates, isTrue);
 
-    group.start('a');
-    expect(group.running, unorderedEquals(['a']));
+    group.start(IsolateRef(id: 'a'));
+    expect(group.running.map((iso) => iso.id).toList(), unorderedEquals(['a']));
     expect(group.paused, isEmpty);
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.start('a');
-    expect(group.running, unorderedEquals(['a']));
+    group.start(IsolateRef(id: 'a'));
+    expect(group.running.map((iso) => iso.id).toList(), unorderedEquals(['a']));
     expect(group.paused, isEmpty);
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.start('b');
-    expect(group.running, unorderedEquals(['a', 'b']));
+    group.start(IsolateRef(id: 'b'));
+    expect(group.running.map((iso) => iso.id).toList(),
+        unorderedEquals(['a', 'b']));
     expect(group.paused, isEmpty);
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.pause('a');
-    expect(group.running, unorderedEquals(['b']));
-    expect(group.paused, unorderedEquals(['a']));
+    group.pause(IsolateRef(id: 'a'));
+    expect(group.running.map((iso) => iso.id).toList(), unorderedEquals(['b']));
+    expect(group.paused.map((iso) => iso.id).toList(), unorderedEquals(['a']));
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.pause('a');
-    expect(group.running, unorderedEquals(['b']));
-    expect(group.paused, unorderedEquals(['a']));
+    group.pause(IsolateRef(id: 'a'));
+    expect(group.running.map((iso) => iso.id).toList(), unorderedEquals(['b']));
+    expect(group.paused.map((iso) => iso.id).toList(), unorderedEquals(['a']));
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.pause('c');
-    expect(group.running, unorderedEquals(['b']));
-    expect(group.paused, unorderedEquals(['a', 'c']));
+    group.pause(IsolateRef(id: 'c'));
+    expect(group.running.map((iso) => iso.id).toList(), unorderedEquals(['b']));
+    expect(group.paused.map((iso) => iso.id).toList(),
+        unorderedEquals(['a', 'c']));
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.start('c');
-    expect(group.running, unorderedEquals(['b', 'c']));
-    expect(group.paused, unorderedEquals(['a']));
+    group.start(IsolateRef(id: 'c'));
+    expect(group.running.map((iso) => iso.id).toList(),
+        unorderedEquals(['b', 'c']));
+    expect(group.paused.map((iso) => iso.id).toList(), unorderedEquals(['a']));
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.pause('c');
-    expect(group.running, unorderedEquals(['b']));
-    expect(group.paused, unorderedEquals(['a', 'c']));
+    group.pause(IsolateRef(id: 'c'));
+    expect(group.running.map((iso) => iso.id).toList(), unorderedEquals(['b']));
+    expect(group.paused.map((iso) => iso.id).toList(),
+        unorderedEquals(['a', 'c']));
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.exit('a');
-    expect(group.running, unorderedEquals(['b']));
-    expect(group.paused, unorderedEquals(['c']));
+    group.exit(IsolateRef(id: 'a'));
+    expect(group.running.map((iso) => iso.id).toList(), unorderedEquals(['b']));
+    expect(group.paused.map((iso) => iso.id).toList(), unorderedEquals(['c']));
     expect(group.noRunningIsolates, isFalse);
     expect(group.noLiveIsolates, isFalse);
 
-    group.pause('b');
+    group.pause(IsolateRef(id: 'b'));
     expect(group.running, isEmpty);
-    expect(group.paused, unorderedEquals(['b', 'c']));
+    expect(group.paused.map((iso) => iso.id).toList(),
+        unorderedEquals(['b', 'c']));
     expect(group.noRunningIsolates, isTrue);
     expect(group.noLiveIsolates, isFalse);
 
-    group.exit('b');
+    group.exit(IsolateRef(id: 'b'));
     expect(group.running, isEmpty);
-    expect(group.paused, unorderedEquals(['c']));
+    expect(group.paused.map((iso) => iso.id).toList(), unorderedEquals(['c']));
     expect(group.noRunningIsolates, isTrue);
     expect(group.noLiveIsolates, isFalse);
 
-    group.exit('c');
+    group.exit(IsolateRef(id: 'c'));
     expect(group.running, isEmpty);
     expect(group.paused, isEmpty);
     expect(group.noRunningIsolates, isTrue);
@@ -528,7 +533,7 @@ void main() {
         service,
         (iso, isLastIsolateInGroup) async {
           expect(stopped, isFalse);
-          received.add('Pause ${iso.id}. Last in group ${iso.isolateGroupId}? '
+          received.add('Pause ${iso.id}. Collect group ${iso.isolateGroupId}? '
               '${isLastIsolateInGroup ? 'Yes' : 'No'}');
         },
         (message) => received.add(message),
@@ -572,23 +577,23 @@ void main() {
       exitEvent('Z', '9');
 
       expect(received, [
-        'Pause A. Last in group 1? No',
+        'Pause A. Collect group 1? No',
         'Resume A',
-        'Pause B. Last in group 1? No',
+        'Pause B. Collect group 1? No',
         'Resume B',
-        'Pause C. Last in group 1? Yes',
+        'Pause C. Collect group 1? Yes',
         'Resume C',
-        'Pause F. Last in group 2? No',
+        'Pause F. Collect group 2? No',
         'Resume F',
-        'Pause E. Last in group 2? No',
+        'Pause E. Collect group 2? No',
         'Resume E',
-        'Pause I. Last in group 3? No',
+        'Pause I. Collect group 3? No',
         'Resume I',
-        'Pause H. Last in group 3? No',
+        'Pause H. Collect group 3? No',
         'Resume H',
-        'Pause D. Last in group 2? Yes',
+        'Pause D. Collect group 2? Yes',
         'Resume D',
-        'Pause G. Last in group 3? Yes',
+        'Pause G. Collect group 3? Yes',
         'Resume G',
       ]);
     });
@@ -614,16 +619,16 @@ void main() {
       // B was paused correctly and was the last to exit isolate 1, so isolate 1
       // was collected ok.
       expect(received, [
-        'Pause B. Last in group 1? Yes',
+        'Pause B. Collect group 1? Yes',
         'Resume B',
-        'Pause D. Last in group 2? No',
+        'Pause D. Collect group 2? No',
         'Resume D',
         'ERROR: An isolate exited without pausing, causing coverage data to '
             'be lost for group 2.',
       ]);
     });
 
-    test('main isolate resumed last', () async {
+    test('subsequent main isolates are ignored', () async {
       startEvent('A', '1', 'main');
       startEvent('B', '1', 'main'); // Second isolate named main, ignored.
       pauseEvent('B', '1', 'main');
@@ -639,17 +644,52 @@ void main() {
       await endTest();
 
       expect(received, [
-        'Pause B. Last in group 1? No',
+        'Pause B. Collect group 1? No',
         'Resume B',
-        'Pause C. Last in group 2? No',
-        'Resume C',
-        'Pause D. Last in group 2? Yes',
-        'Resume D',
-        'Pause A. Last in group 1? Yes',
+        'Pause A. Collect group 1? Yes',
+        'Pause C. Collect group 2? Yes',
         'Resume A',
       ]);
     });
 
+    test('all groups collected as soon as main isolate paused', () async {
+      startEvent('B', '1');
+      startEvent('E', '2');
+      startEvent('D', '2');
+      startEvent('F', '2');
+      pauseEvent('F', '2');
+      startEvent('C', '2');
+      startEvent('A', '1');
+      pauseEvent('B', '1');
+      pauseEvent('E', '2');
+      startEvent('G', '3');
+      pauseEvent('D', '2');
+      startEvent('H', '3');
+      exitEvent('F', '2');
+      startEvent('I', '3');
+      exitEvent('I', '3');
+
+      startEvent('M', '1', 'main');
+      pauseEvent('M', '1', 'main');
+
+      await endTest();
+
+      expect(received, [
+        'Pause F. Collect group 2? No',
+        'Resume F',
+        'Pause B. Collect group 1? No',
+        'Resume B',
+        'Pause E. Collect group 2? No',
+        'Resume E',
+        'Pause D. Collect group 2? No',
+        'Resume D',
+        'Pause M. Collect group 1? Yes',
+        'Pause C. Collect group 2? Yes',
+        'Pause G. Collect group 3? Yes',
+        'Resume M',
+      ]);
+    });
+
     test('main isolate exits without pausing', () async {
       startEvent('A', '1', 'main');
       startEvent('B', '1');
@@ -660,7 +700,7 @@ void main() {
       await endTest();
 
       expect(received, [
-        'Pause B. Last in group 1? No',
+        'Pause B. Collect group 1? No',
         'Resume B',
         'ERROR: An isolate exited without pausing, causing coverage data to '
             'be lost for group 1.',
@@ -674,7 +714,7 @@ void main() {
       await endTest();
 
       expect(received, [
-        'Pause A. Last in group 1? Yes',
+        'Pause A. Collect group 1? Yes',
         'Resume A',
       ]);
     });
@@ -693,9 +733,9 @@ void main() {
       await endTest();
 
       expect(received, [
-        'Pause B. Last in group 1? No',
+        'Pause B. Collect group 1? No',
         'Resume B',
-        'Pause A. Last in group 1? Yes',
+        'Pause A. Collect group 1? Yes',
         'Resume A',
       ]);
     });
@@ -722,11 +762,11 @@ void main() {
       await endTest();
 
       expect(received, [
-        'Pause B. Last in group 1? No',
+        'Pause B. Collect group 1? No',
         'Resume B',
-        'Pause C. Last in group 1? No',
+        'Pause C. Collect group 1? No',
         'Resume C',
-        'Pause A. Last in group 1? Yes',
+        'Pause A. Collect group 1? Yes',
         'Resume A',
       ]);
     });
@@ -753,11 +793,9 @@ void main() {
       await endTest();
 
       expect(received, [
-        'Pause B. Last in group 1? No',
+        'Pause B. Collect group 1? No',
         'Resume B',
-        'Pause C. Last in group 1? Yes',
-        'Resume C',
-        'Pause A. Last in group 1? No',
+        'Pause A. Collect group 1? Yes',
         'Resume A',
       ]);
     });
@@ -795,19 +833,19 @@ void main() {
       await endTest();
 
       expect(received, [
-        'Pause Z. Last in group 9? Yes',
+        'Pause Z. Collect group 9? Yes',
         'Resume Z',
-        'Pause A. Last in group 1? No',
+        'Pause A. Collect group 1? No',
         'Resume A',
-        'Pause B. Last in group 1? Yes',
+        'Pause B. Collect group 1? Yes',
         'Resume B',
-        'Pause E. Last in group 2? No',
+        'Pause E. Collect group 2? No',
         'Resume E',
-        'Pause D. Last in group 2? Yes',
+        'Pause D. Collect group 2? Yes',
         'Resume D',
-        'Pause F. Last in group 2? Yes',
+        'Pause F. Collect group 2? Yes',
         'Resume F',
-        'Pause C. Last in group 1? Yes',
+        'Pause C. Collect group 1? Yes',
         'Resume C',
       ]);
     });
diff --git a/pkgs/coverage/test/run_and_collect_test.dart b/pkgs/coverage/test/run_and_collect_test.dart
index 9c9c943f8..a538a88a5 100644
--- a/pkgs/coverage/test/run_and_collect_test.dart
+++ b/pkgs/coverage/test/run_and_collect_test.dart
@@ -84,7 +84,10 @@ void checkIgnoredLinesInFilesCache(
   expect(ignoredLinesInFilesCache[packageUtilKey], isEmpty);
   expect(ignoredLinesInFilesCache[testAppKey], null /* means whole file */);
   expect(ignoredLinesInFilesCache[testAppIsolateKey], [
-    [52, 52], [54, 58], [63, 66], [67, 73]
+    [52, 52],
+    [54, 58],
+    [63, 66],
+    [67, 73]
   ]);
 }
 

From dc883b08131101983ae6d4838fe8672ddef50c25 Mon Sep 17 00:00:00 2001
From: Liam Appelbe <liama@google.com>
Date: Wed, 9 Apr 2025 13:33:10 +1000
Subject: [PATCH 3/4] changelog

---
 pkgs/coverage/CHANGELOG.md | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pkgs/coverage/CHANGELOG.md b/pkgs/coverage/CHANGELOG.md
index 86e248e7d..7c880fbe2 100644
--- a/pkgs/coverage/CHANGELOG.md
+++ b/pkgs/coverage/CHANGELOG.md
@@ -1,6 +1,9 @@
 ## 1.12.0-wip
 
 - Introduced support for specifying coverage flags through a YAML file.
+- Fix a [bug](https://github.com/dart-lang/tools/issues/2049) where coverage
+  collection could hang forever if the package under test used background
+  isolates that were never shut down.
 
 ## 1.11.1
 

From b6583bf88d82f6c8fa881789c7168ef5f0c2379b Mon Sep 17 00:00:00 2001
From: Liam Appelbe <liama@google.com>
Date: Wed, 9 Apr 2025 13:35:24 +1000
Subject: [PATCH 4/4] Fix analysis

---
 pkgs/coverage/lib/src/isolate_paused_listener.dart  | 1 -
 pkgs/coverage/test/test_files/test_app_isolate.dart | 2 +-
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/pkgs/coverage/lib/src/isolate_paused_listener.dart b/pkgs/coverage/lib/src/isolate_paused_listener.dart
index 5a7591855..28894f772 100644
--- a/pkgs/coverage/lib/src/isolate_paused_listener.dart
+++ b/pkgs/coverage/lib/src/isolate_paused_listener.dart
@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'dart:collection';
-import 'dart:io';
 
 import 'package:meta/meta.dart';
 import 'package:vm_service/vm_service.dart';
diff --git a/pkgs/coverage/test/test_files/test_app_isolate.dart b/pkgs/coverage/test/test_files/test_app_isolate.dart
index 4a2695d8e..22ccd75b3 100644
--- a/pkgs/coverage/test/test_files/test_app_isolate.dart
+++ b/pkgs/coverage/test/test_files/test_app_isolate.dart
@@ -40,7 +40,7 @@ void isolateTask(List threeThings) async {
 
   fooSync(answer);
   unawaited(fooAsync(answer).then((_) {
-    final keepAlive = RawReceivePort()..keepIsolateAlive = true;
+    RawReceivePort().keepIsolateAlive = true;
     final port = threeThings.first as SendPort;
     final sum = (threeThings[1] as int) + (threeThings[2] as int);
     port.send(sum);