[dart:zircon] Porting Cache re-usable handle wait objects (#10809)

Change-Id: I230601acf5de24765737ad81b595fef2c154134c

shell/platform/fuchsia/dart-pkg/zircon/sdk_ext/handle.cc

@@ -16,7 +16,29 @@ namespace dart {
 
 IMPLEMENT_WRAPPERTYPEINFO(zircon, Handle);
 
-Handle::Handle(zx_handle_t handle) : handle_(handle) {}
+Handle::Handle(zx_handle_t handle) : handle_(handle) {
+  tonic::DartState* state = tonic::DartState::Current();
+  FML_DCHECK(state);
+  Dart_Handle zircon_lib = Dart_LookupLibrary(ToDart("dart:zircon"));
+  FML_DCHECK(!tonic::LogIfError(zircon_lib));
+
+  Dart_Handle on_wait_completer_type =
+      Dart_GetClass(zircon_lib, ToDart("_OnWaitCompleteClosure"));
+  FML_DCHECK(!tonic::LogIfError(on_wait_completer_type));
+  on_wait_completer_type_.Set(state, on_wait_completer_type);
+
+  Dart_Handle async_lib = Dart_LookupLibrary(ToDart("dart:async"));
+  FML_DCHECK(!tonic::LogIfError(async_lib));
+  async_lib_.Set(state, async_lib);
+
+  Dart_Handle closure_string = ToDart("_closure");
+  FML_DCHECK(!tonic::LogIfError(closure_string));
+  closure_string_.Set(state, closure_string);
+
+  Dart_Handle schedule_microtask_string = ToDart("scheduleMicrotask");
+  FML_DCHECK(!tonic::LogIfError(schedule_microtask_string));
+  schedule_microtask_string_.Set(state, schedule_microtask_string);
+}
 
 Handle::~Handle() {
   if (is_valid()) {
@@ -93,6 +115,36 @@ Dart_Handle Handle::Duplicate(uint32_t rights) {
   return ToDart(Create(out_handle));
 }
 
+void Handle::ScheduleCallback(tonic::DartPersistentValue callback,
+                              zx_status_t status,
+                              const zx_packet_signal_t* signal) {
+  auto state = callback.dart_state().lock();
+  FML_DCHECK(state);
+  tonic::DartState::Scope scope(state);
+
+  // Make a new _OnWaitCompleteClosure(callback, status, signal->observed).
+  FML_DCHECK(!callback.is_empty());
+  std::vector<Dart_Handle> constructor_args{callback.Release(), ToDart(status),
+                                            ToDart(signal->observed)};
+  Dart_Handle on_wait_complete_closure =
+      Dart_New(on_wait_completer_type_.Get(), Dart_Null(),
+               constructor_args.size(), constructor_args.data());
+  FML_DCHECK(!tonic::LogIfError(on_wait_complete_closure));
+
+  // The _callback field contains the thunk:
+  // () => callback(status, signal->observed)
+  Dart_Handle closure =
+      Dart_GetField(on_wait_complete_closure, closure_string_.Get());
+  FML_DCHECK(!tonic::LogIfError(closure));
+
+  // Put the thunk on the microtask queue by calling scheduleMicrotask().
+  std::vector<Dart_Handle> sm_args{closure};
+  Dart_Handle sm_result =
+      Dart_Invoke(async_lib_.Get(), schedule_microtask_string_.Get(),
+                  sm_args.size(), sm_args.data());
+  FML_DCHECK(!tonic::LogIfError(sm_result));
+}
+
 // clang-format: off
 
 #define FOR_EACH_STATIC_BINDING(V) V(Handle, CreateInvalid)

shell/platform/fuchsia/dart-pkg/zircon/sdk_ext/handle.h

@@ -60,6 +60,10 @@ class Handle : public fml::RefCountedThreadSafe<Handle>,
 
   Dart_Handle Duplicate(uint32_t rights);
 
+  void ScheduleCallback(tonic::DartPersistentValue callback,
+                        zx_status_t status,
+                        const zx_packet_signal_t* signal);
+
  private:
   explicit Handle(zx_handle_t handle);
 
@@ -70,6 +74,13 @@ class Handle : public fml::RefCountedThreadSafe<Handle>,
   zx_handle_t handle_;
 
   std::vector<HandleWaiter*> waiters_;
+
+  // Some cached persistent handles to make running handle wait completers
+  // faster.
+  tonic::DartPersistentValue async_lib_;
+  tonic::DartPersistentValue closure_string_;
+  tonic::DartPersistentValue on_wait_completer_type_;
+  tonic::DartPersistentValue schedule_microtask_string_;
 };
 
 }  // namespace dart

shell/platform/fuchsia/dart-pkg/zircon/sdk_ext/handle_waiter.cc

@@ -81,21 +81,11 @@ void HandleWaiter::OnWaitComplete(async_dispatcher_t* dispatcher,
   // Remove this waiter from the handle.
   handle_->ReleaseWaiter(this);
 
+  // Schedule the callback on the microtask queue.
+  handle_->ScheduleCallback(std::move(callback_), status, signal);
+
   // Clear handle_.
   handle_ = nullptr;
-
-  auto state = callback_.dart_state().lock();
-  FML_DCHECK(state);
-  DartState::Scope scope(state);
-
-  std::vector<Dart_Handle> args{ToDart(status), ToDart(signal->observed)};
-  FML_DCHECK(!callback_.is_empty());
-  Dart_Handle result =
-      Dart_InvokeClosure(callback_.Release(), args.size(), args.data());
-  // If there was an uncaught error from the callback propagate it out.
-  if (tonic::LogIfError(result)) {
-    state->message_handler().UnhandledError(result);
-  }
 }
 
 }  // namespace dart