commit 4715ebd181232cfa2ebfd77f9068ed32449e2415
author Alexander Aprelev <aam@google.com> Mon Jun 09 10:34:40 2025 -0700
committer Commit Queue <dart-scoped@luci-project-accounts.iam.gserviceaccount.com> Mon Jun 09 10:34:40 2025 -0700
tree ea15ba1905b60be8bbe8c1e52402011034c39f20
parent c219974ecffa606ba448c9ab25a097399603556e

[vm/shared] Update mutator count as entering/exiting mutator thread.

Running dart code on mutator thread outside of isolate still should follow limits on number of concurrent mutators in the vm.
Also this fixes inconsistency when entering isolate group as mutator, where original worker was marked as blocked while thread was actually running dart code. That inconsitency showed up as sporadic crash on isolate_group_shared_init_test with increased number of spawned isolates.

TEST=isolate_group_shared_init_test
BUG=https://github.com/dart-lang/sdk/issues/60877

Change-Id: I8917be903bb5517940dad3e5dab143d5ed5fdf79
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/432900
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>

runtime/vm/isolate.cc

diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 3be065c..2806044 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -647,14 +647,11 @@
   }
 }
 
-void IsolateGroup::DecreaseMutatorCount(Isolate* mutator, bool is_nested_exit) {
-  ASSERT(mutator->group() == this);
-
+void IsolateGroup::DecreaseMutatorCount(bool is_nested_exit) {
   // If the mutator thread has an active stack and runs on our thread pool we
   // will mark the worker as blocked, thereby possibly spawning a new worker for
   // pending tasks (if there are any).
   if (is_nested_exit) {
-    ASSERT(mutator->mutator_thread() != nullptr);
     thread_pool()->MarkCurrentWorkerAsBlocked();
   }
 

runtime/vm/isolate.h

diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 01742d4..772d927 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -548,7 +548,7 @@
   void IncreaseMutatorCount(Thread* thread,
                             bool is_nested_reenter,
                             bool was_stolen);
-  void DecreaseMutatorCount(Isolate* mutator, bool is_nested_exit);
+  void DecreaseMutatorCount(bool is_nested_exit);
   NO_SANITIZE_THREAD
   intptr_t MutatorCount() const { return active_mutators_; }
 

runtime/vm/thread.cc

diff --git a/runtime/vm/thread.cc b/runtime/vm/thread.cc
index 4201052..1178afa 100644
--- a/runtime/vm/thread.cc
+++ b/runtime/vm/thread.cc
@@ -489,7 +489,7 @@
   // occupying a mutator again (decreases its max size).
   ASSERT(!(isolate_shutdown && is_nested_exit));
   if (!(is_nested_exit && thread->OwnsSafepoint())) {
-    group->DecreaseMutatorCount(isolate, is_nested_exit);
+    group->DecreaseMutatorCount(is_nested_exit);
   }
 }
 
@@ -538,6 +538,10 @@
   thread->SetStackLimit(OSThread::Current()->overflow_stack_limit());
 #endif
 
+  isolate_group->IncreaseMutatorCount(/*thread=*/thread,
+                                      /*is_nested_reenter=*/false,
+                                      /*was_stolen=*/true);
+
   thread->AssertDartMutatorInvariants();
 }
 
@@ -551,6 +555,7 @@
   thread->ResetMutatorState();
   thread->ClearStackLimit();
   SuspendThreadInternal(thread, VMTag::kInvalidTagId);
+  thread->isolate_group()->DecreaseMutatorCount(/*is_nested_exit=*/true);
   FreeActiveThread(thread, /*isolate=*/nullptr, bypass_safepoint);
 }
 

tests/ffi/isolate_group_shared_init_test.dart

diff --git a/tests/ffi/isolate_group_shared_init_test.dart b/tests/ffi/isolate_group_shared_init_test.dart
index c27e1f46..b9a0f0f 100644
--- a/tests/ffi/isolate_group_shared_init_test.dart
+++ b/tests/ffi/isolate_group_shared_init_test.dart
@@ -42,7 +42,7 @@
 }();
 
 testInitStrings() async {
-  const int nWorkers = 20;
+  const int nWorkers = 100;
   mutex = Mutex();
   final rp = ReceivePort();
   final rpExitAndErrors = ReceivePort()
@@ -78,7 +78,7 @@
 }
 
 testInitThrows() async {
-  const int nWorkers = 20;
+  const int nWorkers = 100;
   final rp = ReceivePort();
   int exitCounter = 0;
   final completer = Completer();