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经过一番尝试，我可以看到：扩展执行与 dart 是异步的，但不是 C，它在当前方法尚未完成时阻塞。

Dart_NativeFunction ResolveName(Dart_Handle name, int argc);
Dart_Handle HandleError(Dart_Handle handle);

void wrapped_method(Dart_Port dest_port_id, Dart_CObject* message) {
  Dart_Port reply_port_id = message->value.as_array.values[0]->value.as_send_port;

  printf("Before sleep\n");
  sleep(5);

  printf("Hello from c !\n");

  Dart_CObject result;
  result.type = Dart_CObject_kBool;
  result.value.as_bool = true;
  Dart_PostCObject(reply_port_id, &result);
}

DART_EXPORT Dart_Handle sample_extension_Init(Dart_Handle parent_library) {                  
  if (Dart_IsError(parent_library)) { return parent_library; }                         
  Dart_Handle result_code = Dart_SetNativeResolver(parent_library, ResolveName);       
    if (Dart_IsError(result_code)) return result_code;                                 
    return Dart_Null();                                                                
}


void sample_extension_ServicePort(Dart_NativeArguments arguments) {                          
  Dart_EnterScope();                                                                   
  Dart_SetReturnValue(arguments, Dart_Null());                                         
  Dart_Port service_port = Dart_NewNativePort("sample_extension_ServicePort",     wrapped_method, true); 
  if (service_port != ILLEGAL_PORT) {                                                  
    Dart_Handle send_port = HandleError(Dart_NewSendPort(service_port));               
    Dart_SetReturnValue(arguments, send_port);                                         
  }                                                                                    
  Dart_ExitScope();                                                                    
}  

struct FunctionLookup {
  const char* name;
  Dart_NativeFunction function;
};

FunctionLookup function_list[] = {
    {"SampleExtension_ServicePort", sample_extension_ServicePort},
    {NULL, NULL}};

Dart_NativeFunction ResolveName(Dart_Handle name, int argc) {                        
  if (!Dart_IsString(name)) return NULL;                                               
  Dart_NativeFunction result = NULL;                                                   
  Dart_EnterScope();                                                                   
  const char* cname;                                                                   
  HandleError(Dart_StringToCString(name, &cname));                                     
  for (int i=0; function_list[i].name != NULL; ++i) {
    if (strcmp(function_list[i].name, cname) == 0) {
      result = function_list[i].function;
      break;
    }
  }
  Dart_ExitScope();                                                                    
  return result;                                                                       
}                                                                                      

Dart_Handle HandleError(Dart_Handle handle) {                                          
  if (Dart_IsError(handle)) Dart_PropagateError(handle);                               
  return handle;                                                                       
}

当我执行 3 次调用服务端口的方法时：

Hello from Dart
Hello from Dart
Before sleep
Hello from Dart
Hello from c !
Before sleep
Hello from c !
Before sleep
Hello from c !

直到每个“来自 c 的你好！”，它的睡眠 5 秒。有一种方法在 C 端也是异步的吗？我见过 ：

DART_EXPORT Dart_Port Dart_NewNativePort(const char* name,
                                     Dart_NativeMessageHandler handler,
                                     bool handle_concurrently);

伟大的 ！但 ...

/* TODO(turnidge): Currently handle_concurrently is ignored. */

这有什么问题吗？（我想投票支持它以遵循解决方案）虽然问题没有解决，但最好的解决方案是什么？在 C fork 中运行代码？

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