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// Copyright (c) 2020, 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.
// Sample showing how to do calls from C into Dart through native ports.
// This sample does not use FFI callbacks to do the callbacks at all. Instead,
// it sends a message to Dart through native ports, decodes the message in Dart
// does a method call in Dart and sends the result back to C through a native
// port.
// The disadvantage of this approach compared to `sample_async_callback.dart`
// is that it requires more boilerplate, because it does not use the automatic
// marshalling of data of the FFI.
// The advantage is that finalizers can be used when passing ownership of data
// (buffers) from C to Dart.
import 'dart:ffi';
import 'dart:isolate';
import 'dart:typed_data';
import 'package:expect/expect.dart';
import '../dylib_utils.dart';
var globalResult = 0;
var numCallbacks1 = 0;
var numCallbacks2 = 0;
main() async {
print("Dart = Dart mutator thread executing Dart.");
print("C Da = Dart mutator thread executing C.");
print("C T1 = Some C thread executing C.");
print("C T2 = Some C thread executing C.");
print("C = C T1 or C T2.");
print("Dart: Setup.");
Expect.isTrue(NativeApi.majorVersion == 2);
Expect.isTrue(NativeApi.minorVersion >= 0);
final initializeApi = dl.lookupFunction<IntPtr Function(Pointer<Void>),
int Function(Pointer<Void>)>("InitDartApiDL");
Expect.isTrue(initializeApi(NativeApi.initializeApiDLData) == 0);
final interactiveCppRequests = ReceivePort()..listen(handleCppRequests);
final int nativePort = interactiveCppRequests.sendPort.nativePort;
print("Dart: Tell C to start worker threads.");
// We need to yield control in order to be able to receive messages.
while (numCallbacks2 < 3) {
print("Dart: Yielding (able to receive messages on port).");
await asyncSleep(500);
print("Dart: Received expected number of callbacks.");
Expect.equals(2, numCallbacks1);
Expect.equals(3, numCallbacks2);
Expect.equals(14, globalResult);
print("Dart: Tell C to stop worker threads.");
print("Dart: Done.");
int myCallback1(int a) {
print("Dart: myCallback1($a).");
return a + 3;
void myCallback2(int a) {
print("Dart: myCallback2($a).");
globalResult += a;
class CppRequest {
final SendPort? replyPort;
final int? pendingCall;
final String method;
final Uint8List data;
factory CppRequest.fromCppMessage(List message) {
return CppRequest._(message[0], message[1], message[2], message[3]);
CppRequest._(this.replyPort, this.pendingCall, this.method,;
String toString() => 'CppRequest(method: $method, ${data.length} bytes)';
class CppResponse {
final int pendingCall;
final Uint8List data;
List toCppMessage() => List.from([pendingCall, data], growable: false);
String toString() => 'CppResponse(message: ${data.length})';
void handleCppRequests(dynamic message) {
final cppRequest = CppRequest.fromCppMessage(message);
print('Dart: Got message: $cppRequest');
if (cppRequest.method == 'myCallback1') {
// Use the data in any way you like. Here we just take the first byte as
// the argument to the function.
final int argument =[0];
final int result = myCallback1(argument);
final cppResponse =
CppResponse(cppRequest.pendingCall!, Uint8List.fromList([result]));
print('Dart: Responding: $cppResponse');
} else if (cppRequest.method == 'myCallback2') {
final int argument =[0];
final dl = dlopenPlatformSpecific("ffi_test_functions");
final registerSendPort = dl.lookupFunction<Void Function(Int64 sendPort),
void Function(int sendPort)>('RegisterSendPort');
final startWorkSimulator2 =
dl.lookupFunction<Void Function(), void Function()>('StartWorkSimulator2');
final stopWorkSimulator2 =
dl.lookupFunction<Void Function(), void Function()>('StopWorkSimulator2');
Future asyncSleep(int ms) {
return new Future.delayed(Duration(milliseconds: ms), () => true);