Add a new getIsolatePauseEvent method in the VM service.

In Flutter hot reload, the flutter_tools are calling the `getIsolate`
to read the pause state of the isolate, which returns a full list of
libraries loaded in the isolate. The size of the return object grow
linearly to the number of Dart files, which can take ~500ms to transfer
for a large app.

This change adds a new method to only read what is needed.

TEST=pkg/vm_service/test/get_isolate_pause_event_rpc_test.dart

Change-Id: If19910cb3ff5d5057932551ac738afd3c3136fac
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/305362
Reviewed-by: Ben Konyi <bkonyi@google.com>
Auto-Submit: Chingjun Lau <chingjun@google.com>
Commit-Queue: Derek Xu <derekx@google.com>

pkg/vm_service/java/.gitignore

@@ -19,6 +19,7 @@ src/org/dartlang/vm/service/consumer/GetInstancesConsumer.java
 src/org/dartlang/vm/service/consumer/GetIsolateConsumer.java
 src/org/dartlang/vm/service/consumer/GetIsolateGroupConsumer.java
 src/org/dartlang/vm/service/consumer/GetIsolateGroupMemoryUsageConsumer.java
+src/org/dartlang/vm/service/consumer/GetIsolatePauseEventConsumer.java
 src/org/dartlang/vm/service/consumer/GetMemoryUsageConsumer.java
 src/org/dartlang/vm/service/consumer/GetObjectConsumer.java
 src/org/dartlang/vm/service/consumer/GetPerfettoCpuSamplesConsumer.java

pkg/vm_service/java/version.properties

@@ -1 +1 @@
-version=4.7
+version=4.8

pkg/vm_service/lib/src/vm_service.dart

@@ -28,7 +28,7 @@ export 'snapshot_graph.dart'
         HeapSnapshotObjectNoData,
         HeapSnapshotObjectNullData;
 
-const String vmServiceVersion = '4.7.0';
+const String vmServiceVersion = '4.8.0';
 
 /// @optional
 const String optional = 'optional';
@@ -216,6 +216,7 @@ Map<String, List<String>> _methodReturnTypes = {
   'getInstancesAsList': const ['InstanceRef'],
   'getIsolate': const ['Isolate'],
   'getIsolateGroup': const ['IsolateGroup'],
+  'getIsolatePauseEvent': const ['Event'],
   'getMemoryUsage': const ['MemoryUsage'],
   'getIsolateGroupMemoryUsage': const ['MemoryUsage'],
   'getScripts': const ['ScriptList'],
@@ -719,6 +720,18 @@ abstract class VmServiceInterface {
   /// returned.
   Future<IsolateGroup> getIsolateGroup(String isolateGroupId);
 
+  /// The `getIsolatePauseEvent` RPC is used to lookup an isolate's pause event
+  /// by its `id`.
+  ///
+  /// If `isolateId` refers to an isolate which has exited, then the `Collected`
+  /// [Sentinel] is returned.
+  ///
+  /// See [Isolate].
+  ///
+  /// This method will throw a [SentinelException] in the case a [Sentinel] is
+  /// returned.
+  Future<Event> getIsolatePauseEvent(String isolateId);
+
   /// The `getMemoryUsage` RPC is used to lookup an isolate's memory usage
   /// statistics by its `id`.
   ///
@@ -1609,6 +1622,11 @@ class VmServerConnection {
             params!['isolateGroupId'],
           );
           break;
+        case 'getIsolatePauseEvent':
+          response = await _serviceImplementation.getIsolatePauseEvent(
+            params!['isolateId'],
+          );
+          break;
         case 'getMemoryUsage':
           response = await _serviceImplementation.getMemoryUsage(
             params!['isolateId'],
@@ -2181,6 +2199,10 @@ class VmService implements VmServiceInterface {
   Future<IsolateGroup> getIsolateGroup(String isolateGroupId) =>
       _call('getIsolateGroup', {'isolateGroupId': isolateGroupId});
 
+  @override
+  Future<Event> getIsolatePauseEvent(String isolateId) =>
+      _call('getIsolatePauseEvent', {'isolateId': isolateId});
+
   @override
   Future<MemoryUsage> getMemoryUsage(String isolateId) =>
       _call('getMemoryUsage', {'isolateId': isolateId});

pkg/vm_service/test/get_isolate_pause_event_rpc_test.dart

@@ -0,0 +1,40 @@
+// Copyright (c) 2023, 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:test/test.dart';
+import 'package:vm_service/vm_service.dart';
+
+import 'common/test_helper.dart';
+
+var tests = <VMTest>[
+  (VmService service) async {
+    final vm = await service.getVM();
+    final result = await service.getIsolatePauseEvent(vm.isolates!.first.id!);
+    expect(result.type, 'Event');
+    expect(result.kind, isNotNull);
+  },
+  // Plausible isolate id, not found.
+  (VmService service) async {
+    try {
+      await service.getIsolatePauseEvent('isolates/9999999999');
+      fail('successfully got isolate with bad ID');
+    } on SentinelException catch (e) {
+      expect(e.sentinel.kind, 'Collected');
+      expect(e.sentinel.valueAsString, '<collected>');
+    }
+  },
+  // Verify that the returned event is the same as returned from getIsolate()
+  (VmService service) async {
+    final vm = await service.getVM();
+    final result = await service.getIsolatePauseEvent(vm.isolates!.first.id!);
+    final isolate = await service.getIsolate(vm.isolates!.first.id!);
+    expect(result.toJson(), isolate.pauseEvent?.toJson());
+  },
+];
+
+main(args) async => runVMTests(
+      args,
+      tests,
+      'get_isolate_pause_event_rpc_test.dart',
+    );

runtime/observatory/tests/service/get_version_rpc_test.dart

@@ -12,7 +12,7 @@ var tests = <VMTest>[
     final result = await vm.invokeRpcNoUpgrade('getVersion', {});
     expect(result['type'], 'Version');
     expect(result['major'], 4);
-    expect(result['minor'], 7);
+    expect(result['minor'], 8);
     expect(result['_privateMajor'], 0);
     expect(result['_privateMinor'], 0);
   },

runtime/observatory_2/tests/service_2/get_version_rpc_test.dart

@@ -12,7 +12,7 @@ var tests = <VMTest>[
     final result = await vm.invokeRpcNoUpgrade('getVersion', {});
     expect(result['type'], equals('Version'));
     expect(result['major'], equals(4));
-    expect(result['minor'], equals(7));
+    expect(result['minor'], equals(8));
     expect(result['_privateMajor'], equals(0));
     expect(result['_privateMinor'], equals(0));
   },

runtime/vm/isolate.cc

@@ -2836,6 +2836,51 @@ static const char* ExceptionPauseInfoToServiceEnum(Dart_ExceptionPauseInfo pi) {
   }
 }
 
+static ServiceEvent IsolatePauseEvent(Isolate* isolate) {
+  if (!isolate->is_runnable()) {
+    // Isolate is not yet runnable.
+    ASSERT((isolate->debugger() == nullptr) ||
+           (isolate->debugger()->PauseEvent() == nullptr));
+    return ServiceEvent(isolate, ServiceEvent::kNone);
+  } else if (isolate->message_handler()->should_pause_on_start()) {
+    if (isolate->message_handler()->is_paused_on_start()) {
+      ASSERT((isolate->debugger() == nullptr) ||
+             (isolate->debugger()->PauseEvent() == nullptr));
+      return ServiceEvent(isolate, ServiceEvent::kPauseStart);
+    } else {
+      // Isolate is runnable but not paused on start.
+      // Some service clients get confused if they see:
+      // NotRunnable -> Runnable -> PausedAtStart
+      // Treat Runnable+ShouldPauseOnStart as NotRunnable so they see:
+      // NonRunnable -> PausedAtStart
+      // The should_pause_on_start flag is set to false after resume.
+      ASSERT((isolate->debugger() == nullptr) ||
+             (isolate->debugger()->PauseEvent() == nullptr));
+      return ServiceEvent(isolate, ServiceEvent::kNone);
+    }
+  } else if (isolate->message_handler()->is_paused_on_exit() &&
+             ((isolate->debugger() == nullptr) ||
+              (isolate->debugger()->PauseEvent() == nullptr))) {
+    return ServiceEvent(isolate, ServiceEvent::kPauseExit);
+  } else if ((isolate->debugger() != nullptr) &&
+             (isolate->debugger()->PauseEvent() != nullptr) &&
+             !isolate->ResumeRequest()) {
+    return *(isolate->debugger()->PauseEvent());
+  } else {
+    ServiceEvent pause_event(isolate, ServiceEvent::kResume);
+
+    if (isolate->debugger() != nullptr) {
+      // TODO(turnidge): Don't compute a full stack trace.
+      DebuggerStackTrace* stack = isolate->debugger()->StackTrace();
+      if (stack->Length() > 0) {
+        pause_event.set_top_frame(stack->FrameAt(0));
+      }
+    }
+
+    return pause_event;
+  }
+}
+
 void Isolate::PrintJSON(JSONStream* stream, bool ref) {
   JSONObject jsobj(stream);
   jsobj.AddProperty("type", (ref ? "@Isolate" : "Isolate"));
@@ -2887,47 +2932,8 @@ void Isolate::PrintJSON(JSONStream* stream, bool ref) {
   jsobj.AddProperty("_isReloading", group()->IsReloading());
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)
 
-  if (!is_runnable()) {
-    // Isolate is not yet runnable.
-    ASSERT((debugger() == nullptr) || (debugger()->PauseEvent() == nullptr));
-    ServiceEvent pause_event(this, ServiceEvent::kNone);
-    jsobj.AddProperty("pauseEvent", &pause_event);
-  } else if (message_handler()->should_pause_on_start()) {
-    if (message_handler()->is_paused_on_start()) {
-      ASSERT((debugger() == nullptr) || (debugger()->PauseEvent() == nullptr));
-      ServiceEvent pause_event(this, ServiceEvent::kPauseStart);
-      jsobj.AddProperty("pauseEvent", &pause_event);
-    } else {
-      // Isolate is runnable but not paused on start.
-      // Some service clients get confused if they see:
-      // NotRunnable -> Runnable -> PausedAtStart
-      // Treat Runnable+ShouldPauseOnStart as NotRunnable so they see:
-      // NonRunnable -> PausedAtStart
-      // The should_pause_on_start flag is set to false after resume.
-      ASSERT((debugger() == nullptr) || (debugger()->PauseEvent() == nullptr));
-      ServiceEvent pause_event(this, ServiceEvent::kNone);
-      jsobj.AddProperty("pauseEvent", &pause_event);
-    }
-  } else if (message_handler()->is_paused_on_exit() &&
-             ((debugger() == nullptr) ||
-              (debugger()->PauseEvent() == nullptr))) {
-    ServiceEvent pause_event(this, ServiceEvent::kPauseExit);
-    jsobj.AddProperty("pauseEvent", &pause_event);
-  } else if ((debugger() != nullptr) && (debugger()->PauseEvent() != nullptr) &&
-             !ResumeRequest()) {
-    jsobj.AddProperty("pauseEvent", debugger()->PauseEvent());
-  } else {
-    ServiceEvent pause_event(this, ServiceEvent::kResume);
-
-    if (debugger() != nullptr) {
-      // TODO(turnidge): Don't compute a full stack trace.
-      DebuggerStackTrace* stack = debugger()->StackTrace();
-      if (stack->Length() > 0) {
-        pause_event.set_top_frame(stack->FrameAt(0));
-      }
-    }
-    jsobj.AddProperty("pauseEvent", &pause_event);
-  }
+  ServiceEvent pause_event = IsolatePauseEvent(this);
+  jsobj.AddProperty("pauseEvent", &pause_event);
 
   const Library& lib = Library::Handle(group()->object_store()->root_library());
   if (!lib.IsNull()) {
@@ -3003,6 +3009,10 @@ void Isolate::PrintMemoryUsageJSON(JSONStream* stream) {
   group()->heap()->PrintMemoryUsageJSON(stream);
 }
 
+void Isolate::PrintPauseEventJSON(JSONStream* stream) {
+  IsolatePauseEvent(this).PrintJSON(stream);
+}
+
 #endif
 
 void Isolate::set_tag_table(const GrowableObjectArray& value) {

runtime/vm/isolate.h

@@ -1268,6 +1268,8 @@ class Isolate : public BaseIsolate, public IntrusiveDListEntry<Isolate> {
   // Creates an object with the total heap memory usage statistics for this
   // isolate.
   void PrintMemoryUsageJSON(JSONStream* stream);
+
+  void PrintPauseEventJSON(JSONStream* stream);
 #endif
 
 #if !defined(PRODUCT)

runtime/vm/service.cc

@@ -1623,6 +1623,15 @@ static void GetIsolateGroupMemoryUsage(Thread* thread, JSONStream* js) {
   });
 }
 
+static const MethodParameter* const get_isolate_pause_event_params[] = {
+    ISOLATE_PARAMETER,
+    nullptr,
+};
+
+static void GetIsolatePauseEvent(Thread* thread, JSONStream* js) {
+  thread->isolate()->PrintPauseEventJSON(js);
+}
+
 static const MethodParameter* const get_scripts_params[] = {
     RUNNABLE_ISOLATE_PARAMETER,
     nullptr,
@@ -5821,6 +5830,8 @@ static const ServiceMethodDescriptor service_methods_[] = {
     get_isolate_metric_params },
   { "_getIsolateMetricList", GetIsolateMetricList,
     get_isolate_metric_list_params },
+  { "getIsolatePauseEvent", GetIsolatePauseEvent,
+    get_isolate_pause_event_params },
   { "getObject", GetObject,
     get_object_params },
   { "_getObjectStore", GetObjectStore,

runtime/vm/service.h

@@ -17,7 +17,7 @@
 namespace dart {
 
 #define SERVICE_PROTOCOL_MAJOR_VERSION 4
-#define SERVICE_PROTOCOL_MINOR_VERSION 7
+#define SERVICE_PROTOCOL_MINOR_VERSION 8
 
 class Array;
 class EmbedderServiceHandler;

runtime/vm/service/service.md

@@ -1,8 +1,8 @@
-# Dart VM Service Protocol 4.7
+# Dart VM Service Protocol 4.8
 
 > Please post feedback to the [observatory-discuss group][discuss-list]
 
-This document describes of _version 4.7_ of the Dart VM Service Protocol. This
+This document describes of _version 4.8_ of the Dart VM Service Protocol. This
 protocol is used to communicate with a running Dart Virtual Machine.
 
 To use the Service Protocol, start the VM with the *--observe* flag.
@@ -49,6 +49,7 @@ The Service Protocol uses [JSON-RPC 2.0][].
   - [getIsolate](#getisolate)
   - [getIsolateGroup](#getisolategroup)
   - [getMemoryUsage](#getmemoryusage)
+  - [getIsolatePauseEvent](#getisolatePauseEvent)
   - [getObject](#getobject)
   - [getPerfettoCpuSamples](#getperfettocpusamples)
   - [getPerfettoVMTimeline](#getperfettovmtimeline)
@@ -953,6 +954,20 @@ _IsolateGroup_ _id_ is an opaque identifier that can be fetched from an
 
 See [IsolateGroup](#isolategroup), [VM](#vm).
 
+### getIsolatePauseEvent
+
+```
+Event|Sentinel getIsolatePauseEvent(string isolateId)
+```
+
+The _getIsolatePauseEvent_ RPC is used to lookup an isolate's pause event by its
+_id_.
+
+If _isolateId_ refers to an isolate which has exited, then the
+_Collected_ [Sentinel](#sentinel) is returned.
+
+See [Isolate](#isolate).
+
 ### getMemoryUsage
 
 ```
@@ -4676,5 +4691,6 @@ version | comments
 4.5 | Added `getPerfettoVMTimeline` RPC.
 4.6 | Added `getPerfettoCpuSamples` RPC. Added a deprecation notice to `InstanceKind.TypeRef`.
 4.7 | Added a deprecation notice to `Stack.awaiterFrames` field. Added a deprecation notice to `FrameKind.AsyncActivation`.
+4.8 | Added `getIsolatePauseEvent` RPC.
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss