Implement safepointing of threads

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 8a9e31ecf3ecb99fbf2fba69486d8b3804c142d9..7f1c6f7d3c157576493cf907c4ddba7126b1451e 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -357,6 +357,24 @@ static RawObject* Send1Arg(const Instance& receiver,
 }
 
 
+static const char* GetErrorString(Thread* thread, const Object& obj) {
+  if (obj.IsError()) {
+    const Error& error = Error::Cast(obj);
+    const char* str = error.ToErrorCString();
+    intptr_t len = strlen(str) + 1;
+    char* str_copy = Api::TopScope(thread)->zone()->Alloc<char>(len);
+    strncpy(str_copy, str, len);
+    // Strip a possible trailing '\n'.
+    if ((len > 1) && (str_copy[len - 2] == '\n')) {
+      str_copy[len - 2] = '\0';
+    }
+    return str_copy;
+  } else {
+    return "";
+  }
+}
+
+
 Dart_Handle Api::InitNewHandle(Thread* thread, RawObject* raw) {
   LocalHandles* local_handles = Api::TopScope(thread)->local_handles();
   ASSERT(local_handles != NULL);
@@ -451,7 +469,9 @@ Dart_Isolate Api::CastIsolate(Isolate* isolate) {
 
 
 Dart_Handle Api::NewError(const char* format, ...) {
-  DARTSCOPE(Thread::Current());
+  Thread* T = Thread::Current();
+  CHECK_API_SCOPE(T);
+  HANDLESCOPE(T);
   CHECK_CALLBACK_STATE(T);
 
   va_list args;
@@ -748,20 +768,7 @@ DART_EXPORT const char* Dart_GetError(Dart_Handle handle) {
   API_TIMELINE_DURATION;
   DARTSCOPE(Thread::Current());
   const Object& obj = Object::Handle(Z, Api::UnwrapHandle(handle));
-  if (obj.IsError()) {
-    const Error& error = Error::Cast(obj);
-    const char* str = error.ToErrorCString();
-    intptr_t len = strlen(str) + 1;
-    char* str_copy = Api::TopScope(T)->zone()->Alloc<char>(len);
-    strncpy(str_copy, str, len);
-    // Strip a possible trailing '\n'.
-    if ((len > 1) && (str_copy[len - 2] == '\n')) {
-      str_copy[len - 2] = '\0';
-    }
-    return str_copy;
-  } else {
-    return "";
-  }
+  return GetErrorString(T, obj);
 }
 
 
@@ -818,7 +825,8 @@ DART_EXPORT Dart_Handle Dart_NewUnhandledExceptionError(Dart_Handle exception) {
   Instance& obj = Instance::Handle(Z);
   intptr_t class_id = Api::ClassId(exception);
   if ((class_id == kApiErrorCid) || (class_id == kLanguageErrorCid)) {
-    obj = String::New(::Dart_GetError(exception));
+    const Object& excp = Object::Handle(Z, Api::UnwrapHandle(exception));
+    obj = String::New(GetErrorString(T, excp));
   } else {
     obj = Api::UnwrapInstanceHandle(Z, exception).raw();
     if (obj.IsNull()) {
@@ -1033,6 +1041,7 @@ DART_EXPORT Dart_WeakPersistentHandle Dart_NewWeakPersistentHandle(
   if (callback == NULL) {
     return NULL;
   }
+  TransitionNativeToVM transition(thread);
   return AllocateFinalizableHandle(thread,
                                    object,
                                    peer,
@@ -1251,6 +1260,8 @@ DART_EXPORT Dart_Isolate Dart_CreateIsolate(const char* script_uri,
   #endif  // defined(DART_NO_SNAPSHOT).
       // We exit the API scope entered above.
       Dart_ExitScope();
+      T->set_execution_state(Thread::kThreadInNative);
+      T->EnterSafepoint();
       return Api::CastIsolate(I);
     }
     *error = strdup(error_obj.ToErrorCString());
@@ -1271,6 +1282,8 @@ DART_EXPORT void Dart_ShutdownIsolate() {
     HandleScope handle_scope(T);
     Dart::RunShutdownCallback();
   }
+  T->ExitSafepoint();
+  T->set_execution_state(Thread::kThreadInVM);
   Dart::ShutdownIsolate();
 }
 
@@ -1314,6 +1327,9 @@ DART_EXPORT void Dart_EnterIsolate(Dart_Isolate isolate) {
   if (!Thread::EnterIsolate(iso)) {
     FATAL("Unable to Enter Isolate as Dart VM is shutting down");
   }
+  Thread* T = Thread::Current();
+  T->set_execution_state(Thread::kThreadInNative);
+  T->EnterSafepoint();
 }
 
 
@@ -1532,6 +1548,9 @@ DART_EXPORT Dart_Handle Dart_RunLoop() {
     if (!Thread::EnterIsolate(I)) {
       FATAL("Inconsistent state, VM shutting down while in run loop.");
     }
+    Thread* thread = Thread::Current();

[zra, 2016/01/08 23:32:07]

It looks like TransitionNativeToVM transition(thread) and DARTSCOPE manage the
thread state and safepoints automagically, but sometimes they're managed
manually, like here.

In places where they're managed manually, and there isn't a matching enter/exit
safepoint or set/unset thread state nearby, it would be helpful to know where
the matching calls are.

[siva, 2016/01/12 21:26:22]

DARTSCOPE has a TransitionNativeToVM in it which transitions the state on entry
and restores it back on exit. This works nicely for most calls but EnterIsolate
and ExitIsolate are special as the Thread is unscheduled on exit and we might
get scheduled on a different Thread structure on EnterIsolate so using a Stack
allocated object like TransitionNativeToVM would not work in that case and hence
the explicit code that transitions.

I will add a comment to make this clear.

+    thread->set_execution_state(Thread::kThreadInNative);
+    thread->EnterSafepoint();
   }
   if (I->object_store()->sticky_error() != Object::null()) {
     Dart_Handle error = Api::NewHandle(T, I->object_store()->sticky_error());
@@ -1552,6 +1571,7 @@ DART_EXPORT Dart_Handle Dart_HandleMessage() {
   CHECK_API_SCOPE(T);
   CHECK_CALLBACK_STATE(T);
   API_TIMELINE_BEGIN_END;
+  TransitionNativeToVM trainsition(T);
   if (I->message_handler()->HandleNextMessage() != MessageHandler::kOK) {
     Dart_Handle error = Api::NewHandle(T, I->object_store()->sticky_error());
     I->object_store()->clear_sticky_error();
@@ -1567,6 +1587,7 @@ DART_EXPORT bool Dart_HandleServiceMessages() {
   CHECK_API_SCOPE(T);
   CHECK_CALLBACK_STATE(T);
   API_TIMELINE_DURATION;
+  TransitionNativeToVM trainsition(T);
   ASSERT(I->GetAndClearResumeRequest() == false);
   MessageHandler::MessageStatus status =
       I->message_handler()->HandleOOBMessages();
@@ -4847,10 +4868,11 @@ DART_EXPORT void Dart_SetWeakHandleReturnValue(Dart_NativeArguments args,
 // --- Environment ---
 RawString* Api::CallEnvironmentCallback(Thread* thread, const String& name) {
   Isolate* isolate = thread->isolate();
-  Scope api_scope(thread);
   Dart_EnvironmentCallback callback = isolate->environment_callback();
   String& result = String::Handle(thread->zone());
   if (callback != NULL) {
+    TransitionVMToNative transition(thread);
+    Scope api_scope(thread);
     Dart_Handle response = callback(Api::NewHandle(thread, name.raw()));
     if (::Dart_IsString(response)) {
       result ^= Api::UnwrapHandle(response);