Remove and Add the mutator thread from the active thread list when unscheduling and scheduling the …

runtime/vm/thread_registry.cc

Index: runtime/vm/thread_registry.cc
diff --git a/runtime/vm/thread_registry.cc b/runtime/vm/thread_registry.cc
index 0d36e0d2575cac44dc1d0474baf0cbe140db0bc8..9a57793682d037ea006c2692888e7920d1dcd84d 100644
--- a/runtime/vm/thread_registry.cc
+++ b/runtime/vm/thread_registry.cc
@@ -13,12 +13,10 @@ ThreadRegistry::~ThreadRegistry() {
   // Go over the free thread list and delete the thread objects.
   {
     MonitorLocker ml(monitor_);
-    // At this point the mutator thread should be the only thread
-    // in the active list, delete it.
-    ASSERT(active_list_->next_ == NULL);
-    ASSERT(active_list_ == mutator_thread_);
+    // At this point the active list should be empty.
+    ASSERT(active_list_ == NULL);
+    // We have cached the mutator thread, delete it.
     delete mutator_thread_;
-    active_list_ = NULL;
     mutator_thread_ = NULL;
     // Now delete all the threads in the free list.
     while (free_list_ != NULL) {
@@ -80,6 +78,8 @@ Thread* ThreadRegistry::Schedule(Isolate* isolate,
   OSThread* os_thread = OSThread::Current();
   ASSERT(os_thread != NULL);
   ASSERT(isolate->heap() != NULL);
+  // First get a Thread structure. (we special case the mutator thread
+  // by reusing the cached structure, see comment in 'thread_registry.h').
   if (is_mutator) {
     if (mutator_thread_ == NULL) {
       mutator_thread_ = GetThreadFromFreelist(isolate);
@@ -89,6 +89,9 @@ Thread* ThreadRegistry::Schedule(Isolate* isolate,
     thread = GetThreadFromFreelist(isolate);
     ASSERT(thread->api_top_scope() == NULL);
   }
+  // Now add this Thread to the active list for the isolate.
+  AddThreadToActiveList(thread);
+  // Set up other values and set the TLS value.
   thread->isolate_ = isolate;
   thread->heap_ = isolate->heap();
   thread->set_os_thread(os_thread);
@@ -111,6 +114,10 @@ void ThreadRegistry::Unschedule(Thread* thread,
   thread->isolate_ = NULL;
   thread->heap_ = NULL;
   thread->set_os_thread(NULL);
+  // Remove thread from the active list for the isolate.
+  RemoveThreadFromActiveList(thread);
+  // Return thread to the free list (we special case the mutator
+  // thread by holding on to it, see comment in 'thread_registry.h').
   if (!is_mutator) {
     ASSERT(thread->api_top_scope() == NULL);
     ReturnThreadToFreelist(thread);
@@ -147,29 +154,17 @@ void ThreadRegistry::VisitObjectPointers(ObjectPointerVisitor* visitor,
 }
 
 
-Thread* ThreadRegistry::GetThreadFromFreelist(Isolate* isolate) {
+void ThreadRegistry::AddThreadToActiveList(Thread* thread) {
+  ASSERT(thread != NULL);
   ASSERT(monitor_->IsOwnedByCurrentThread());
-  Thread* thread = NULL;
-  // Get thread structure from free list or create a new one.
-  if (free_list_ == NULL) {
-    thread = new Thread(isolate);
-  } else {
-    thread = free_list_;
-    free_list_ = thread->next_;
-  }
-  // Add thread to active list.
   thread->next_ = active_list_;
   active_list_ = thread;
-  return thread;
 }
 
-void ThreadRegistry::ReturnThreadToFreelist(Thread* thread) {
+
+void ThreadRegistry::RemoveThreadFromActiveList(Thread* thread) {
   ASSERT(thread != NULL);
-  ASSERT(thread->os_thread_ == NULL);
-  ASSERT(thread->isolate_ == NULL);
-  ASSERT(thread->heap_ == NULL);
   ASSERT(monitor_->IsOwnedByCurrentThread());
-  // First remove the thread from the active list.
   Thread* prev = NULL;
   Thread* current = active_list_;
   while (current != NULL) {
@@ -184,7 +179,29 @@ void ThreadRegistry::ReturnThreadToFreelist(Thread* thread) {
     prev = current;
     current = current->next_;
   }
-  // Now add thread to the free list.
+}
+
+
+Thread* ThreadRegistry::GetThreadFromFreelist(Isolate* isolate) {
+  ASSERT(monitor_->IsOwnedByCurrentThread());
+  Thread* thread = NULL;
+  // Get thread structure from free list or create a new one.
+  if (free_list_ == NULL) {
+    thread = new Thread(isolate);
+  } else {
+    thread = free_list_;
+    free_list_ = thread->next_;
+  }
+  return thread;
+}
+
+void ThreadRegistry::ReturnThreadToFreelist(Thread* thread) {
+  ASSERT(thread != NULL);
+  ASSERT(thread->os_thread_ == NULL);
+  ASSERT(thread->isolate_ == NULL);
+  ASSERT(thread->heap_ == NULL);
+  ASSERT(monitor_->IsOwnedByCurrentThread());
+  // Add thread to the free list.
   thread->next_ = free_list_;
   free_list_ = thread;
 }