node/electron插件: 由监听 Windows 打印机状态功能深入理解原生node插件编写过程

"RuntimeLibrary": 2, #MultiThreadedDLL /MD
"Optimization": 2,
"RuntimeTypeInfo": "true",
"CompileAsManaged": "true", # /clr
"DebugInformationFormat": 3, #ProgramDatabase /Zi
"ExceptionHandling": 0, #Async /EHa
"BasicRuntimeChecks": 0, #Default

#pragma unmanaged

// safe_async_worker.h
template <typename T>
class SafeAsyncWorker : public Napi::ObjectWrap<T>
{
public:
  SafeAsyncWorker(const Napi::CallbackInfo &info);

protected:
  virtual void Execute() = 0;
  virtual Napi::Value Parse(napi_env env, void *data) = 0;
  virtual void Free(void *data) = 0;

  // Create a thread-safe function and an async queue work item. We pass the
  // thread-safe function to the async queue work item so the latter might have a
  // chance to call into JavaScript from the worker thread on which the
  // ExecuteWork callback runs.
  Napi::Value CreateAsyncWork(const Napi::CallbackInfo &cb);

  // This function runs on a worker thread. It has no access to the JavaScript
  // environment except through the thread-safe function.
  static void OnExecuteWork(napi_env env, void *data);

  // This function runs on the main thread after `ExecuteWork` exits.
  static void OnWorkComplete(napi_env env, napi_status status, void *data);

  // This function is responsible for converting data coming in from the worker
  // thread to napi_value items that can be passed into JavaScript, and for
  // calling the JavaScript function.
  static void OnCallJavaScript(napi_env env, napi_value js_cb, void *context, void *data);

  void SubmitWork(void *data);

  static Napi::FunctionReference constructor;

private:
  napi_async_work work;
  napi_threadsafe_function tsfn;
};

// safe_async_worker.inl
template <typename T>
Napi::FunctionReference SafeAsyncWorker<T>::constructor;

template <typename T>
inline SafeAsyncWorker<T>::SafeAsyncWorker(const Napi::CallbackInfo &info)
    : Napi::ObjectWrap<T>(info)
{
}

template <typename T>
void printer::SafeAsyncWorker<T>::SubmitWork(void *data)
{
  // Initiate the call into JavaScript. The call into JavaScript will not
  // have happened when this function returns, but it will be queued.
  assert(napi_call_threadsafe_function(tsfn, data, napi_tsfn_blocking) == napi_ok);
}

template <typename T>
Napi::Value SafeAsyncWorker<T>::CreateAsyncWork(const Napi::CallbackInfo &cb)
{
  Napi::Env env = cb.Env();
  napi_value work_name;

  // Create a string to describe this asynchronous operation.
  assert(napi_create_string_utf8(env,
                                 typeid(T).name(),
                                 NAPI_AUTO_LENGTH,
                                 &work_name) == napi_ok);

  // Convert the callback retrieved from JavaScript into a thread-safe function
  // which we can call from a worker thread.
  assert(napi_create_threadsafe_function(env,
                                         cb[0],
                                         NULL,
                                         work_name,
                                         0,
                                         1,
                                         NULL,
                                         NULL,
                                         this,
                                         OnCallJavaScript,
                                         &(tsfn)) == napi_ok);

  // Create an async work item, passing in the addon data, which will give the
  // worker thread access to the above-created thread-safe function.
  assert(napi_create_async_work(env,
                                NULL,
                                work_name,
                                OnExecuteWork,
                                OnWorkComplete,
                                this,
                                &(work)) == napi_ok);

  // Queue the work item for execution.
  assert(napi_queue_async_work(env, work) == napi_ok);

  // This causes `undefined` to be returned to JavaScript.
  return env.Undefined();
}

template <typename T>
void SafeAsyncWorker<T>::OnExecuteWork(napi_env /*env*/, void *this_pointer)
{
  T *self = static_cast<T *>(this_pointer);

  // We bracket the use of the thread-safe function by this thread by a call to
  // napi_acquire_threadsafe_function() here, and by a call to
  // napi_release_threadsafe_function() immediately prior to thread exit.
  assert(napi_acquire_threadsafe_function(self->tsfn) == napi_ok);
#ifdef NAPI_CPP_EXCEPTIONS
  try
  {
    self->Execute();
  }
  catch (const std::exception &e)
  {
    // TODO
  }
#else  // NAPI_CPP_EXCEPTIONS
  self->Execute();
#endif // NAPI_CPP_EXCEPTIONS

  // Indicate that this thread will make no further use of the thread-safe function.
  assert(napi_release_threadsafe_function(self->tsfn,
                                          napi_tsfn_release) == napi_ok);
}

template <typename T>
void SafeAsyncWorker<T>::OnWorkComplete(napi_env env, napi_status status, void *this_pointer)
{
  T *self = (T *)this_pointer;

  // Clean up the thread-safe function and the work item associated with this
  // run.
  assert(napi_release_threadsafe_function(self->tsfn,
                                          napi_tsfn_release) == napi_ok);
  assert(napi_delete_async_work(env, self->work) == napi_ok);

  // Set both values to NULL so JavaScript can order a new run of the thread.
  self->work = NULL;
  self->tsfn = NULL;
}

template <typename T>
void SafeAsyncWorker<T>::OnCallJavaScript(napi_env env, napi_value js_cb, void *this_pointer, void *data)
{
  T *self = static_cast<T *>(this_pointer);
  if (env != NULL)
  {
    napi_value undefined;
#ifdef NAPI_CPP_EXCEPTIONS
    try
    {
      napi_value js_value = self->Parse(env, data);
    }
    catch (const std::exception &e)
    {
      // TODO
    }
#else  // NAPI_CPP_EXCEPTIONS
    napi_value js_value = self->Parse(env, data);
#endif // NAPI_CPP_EXCEPTIONS

    // Retrieve the JavaScript `undefined` value so we can use it as the `this`
    // value of the JavaScript function call.
    assert(napi_get_undefined(env, &undefined) == napi_ok);

    // Call the JavaScript function and pass it the prime that the secondary
    // thread found.
    assert(napi_call_function(env,
                              undefined,
                              js_cb,
                              1,
                              &js_value,
                              NULL) == napi_ok);
  }
  self->Free(data);
}