[vm/shared] Ensure Resume stub works in absence of isolate.

The stub can be invoked from isolategroup-bound code.

Also require set experimental-shared-data flag when using IsolateGroup.runSync.

TEST=vm/dart/shared_syncstar_test
BUG=#61137

Change-Id: I2af27f3f9eeb0dd0dbdfe2e4ec5b162a8e0bd816
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/441260
Reviewed-by: Ryan Macnak <[email protected]>
Commit-Queue: Alexander Aprelev <[email protected]>

Author: aam

runtime/lib/concurrent.cc

@@ -115,6 +115,12 @@ DEFINE_FFI_NATIVE_ENTRY(ConditionVariable_NotifyAll,
 DEFINE_FFI_NATIVE_ENTRY(IsolateGroup_runSync,
                         Dart_Handle,
                         (Dart_Handle closure)) {
+  if (!FLAG_experimental_shared_data) {
+    FATAL(
+        "Encountered shared data api when functionality is disabled. "
+        "Pass --experimental-shared-data");
+  }
+
   Thread* current_thread = Thread::Current();
   ASSERT(current_thread->execution_state() == Thread::kThreadInNative);
   Isolate* saved_isolate = current_thread->isolate();

runtime/tests/vm/dart/shared_syncstar_test.dart

@@ -0,0 +1,18 @@
+// 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.
+//
+// VMOptions=--experimental-shared-data
+//
+import 'dart:_internal' show VMInternalsForTesting;
+import 'package:dart_internal/isolate_group.dart' show IsolateGroup;
+
+Iterable<int> syncStar() sync* {
+  yield 0;
+}
+
+main() {
+  IsolateGroup.runSync(() {
+    syncStar().iterator.moveNext();
+  });
+}

runtime/vm/compiler/stub_code_compiler.cc

@@ -2422,11 +2422,15 @@ void StubCodeCompiler::GenerateResumeStub() {
 #if !defined(PRODUCT)
     // Check if there is a breakpoint at resumption.
     __ LoadIsolate(kTemp);
+    Label skip_breakpoints_check;
+    // Skip check if no isolate is available(running isolategroup-bound code)
+    __ BranchIfZero(kTemp, &skip_breakpoints_check);
     __ LoadFromOffset(kTemp, kTemp,
                       target::Isolate::has_resumption_breakpoints_offset(),
                       kUnsignedByte);
     __ CompareImmediate(kTemp, 0);
     __ BranchIf(NOT_EQUAL, &call_runtime);
+    __ Bind(&skip_breakpoints_check);
 #endif
   }