Question

对于上下文，我从this问题开始。我需要在另一个线程中调用发射器的回调。我做了一个最小的示例，但它在emit.Call({cb, result});上存在段错误。我的第一个直觉是我对env或emit函数的生存期存在疑问。

addon.cpp

#include <napi.h>
#include <iostream>
#include <thread>
#include <memory>
#include <functional>
#include <chrono>

std::shared_ptr<std::thread> thread;
bool running = true;

void generate(Napi::Env& env, Napi::Function& emit)
{
  while(running)
  {
    Napi::Array result = Napi::Array::New(env);

    for(int i = 0; i < 3; ++i)
    {
      result[i] = rand()%100;
    }

    auto cb = Napi::String::New(env, "onFeedData");

    emit.Call({cb, result});

    std::this_thread::sleep_for(std::chrono::seconds(1));
  }
}

Napi::Value Start(const Napi::CallbackInfo& info)
{
  Napi::Env env = info.Env();
  Napi::Function emit = info[0].As<Napi::Function>();

  auto cb = std::bind(generate, env, emit);
  thread = std::make_shared<std::thread>(cb);

  return Napi::String::New(env, "OK");
}

Napi::Value Stop(const Napi::CallbackInfo& info)
{
  Napi::Env env = info.Env();
  Napi::Function emit = info[0].As<Napi::Function>();

  running = false;
  thread->join();

  return Napi::String::New(env, "OK");
}

Napi::Object Init(Napi::Env env, Napi::Object exports)
{
  exports.Set(
      Napi::String::New(env, "Start"),
      Napi::Function::New(env, Start));

  exports.Set(Napi::String::New(env, "Stop"),
      Napi::Function::New(env, Stop));

  return exports;
}

NODE_API_MODULE(addon, Init)

index.js

'use strict'

const EventEmitter = require('events').EventEmitter;
const addon = require('./build/addon.node');

function Main() {
  const emitter = new EventEmitter();

  emitter.on('onFeedData', (evt) => {
    console.log(evt);
  })

  setTimeout(() => {
    addon.Stop( emitter.emit.bind(emitter) );
  }, 5000);

  addon.Start( emitter.emit.bind(emitter) );
}

Main();

Answer 1

I have not tried this, still I know the The node.js v10.6 has introduce Asynchronous Thread-safe Function Calls, it is still in experimental state with Stability level 1. The usage has certain limitation too, here is the snippet from the node.js documentation.

JavaScript functions can normally only be called from a native addon's main thread. If an addon creates additional threads, then N-API functions that require a napi_env, napi_value, or napi_ref must not be called from those threads.

When an addon has additional threads and JavaScript functions need to be invoked based on the processing completed by those threads, those threads must communicate with the addon's main thread so that the main thread can invoke the JavaScript function on their behalf. The thread-safe function APIs provide an easy way to do this.

You can get the full documentation about it from. Asynchronous Thread-safe Function Calls

Answer 2

我尝试了许多解决方案，但只有此方法可以解决。

使用napi-thread-safe-callback，您可以安全地从子线程回调：

void example_async_work(const CallbackInfo& info)
{
    // Capture callback in main thread
    auto callback = std::make_shared<ThreadSafeCallback>(info[0].As<Function>());
    bool fail = info.Length() > 1;

    // Pass callback to other thread
    std::thread([callback, fail]
    {
        try
        {
            // Do some work to get a result
            if (fail)
                throw std::runtime_error("Failure during async work");
            std::string result = "foo";

            // Call back with result
            callback->call([result](Napi::Env env, std::vector<napi_value>& args)
            {
                // This will run in main thread and needs to construct the
                // arguments for the call
                args = { env.Undefined(), Napi::String::New(env, result) };
            });
        }
        catch (std::exception& e)
        {
            // Call back with error
            callback->callError(e.what());
        }
    }).detach();
}

如何在插件中从单独的c ++线程调用发射器回调？

2 个答案: