从C ++代码调用JavaScript回调函数引发错误-nbind [英] calling JavaScript callback function from C++ code throwing errors - nbind
问题描述
我正尝试注册一个JavaScript回调函数,以便以后从C ++类调用。我正在使用 nbind 制作一个node.js插件。我编写的一些示例代码包含一些需要完成同一操作的更复杂的代码:
I'm trying to register a JavaScript callback function to be called from a C++ class later. I'm using nbind to make a node.js addon. This some sample code I've written of some more complex code that needs to accomplish the same thing:
c ++代码(testing.cc):
the c++ code (testing.cc):
#include "nbind/api.h"
#include <string>
#include <iostream>
class Test
{
nbind::cbFunction *callback;
public:
Test() {}
//this dummy var is only here so that doCallback() will be recognized as a function
void doCallback(int dummyVar)
{
std::cout << "Calling Javascript callback" << std::endl;
//call javascript code
if (callback != nullptr)
{
(*callback)("Hi there!\n");
}
return;
}
void enrollCallback(nbind::cbFunction &cb)
{
callback = &cb;
return;
}
};
#include "nbind/nbind.h"
NBIND_CLASS(Test) {
construct<>();
method(doCallback);
method(enrollCallback);
method(unenrollCallback);
}
JavaScript代码(test.js):
the JavaScript code (test.js):
var nbind = require('nbind');
function printMessage(message) {
console.log(message);
}
var lib = nbind.init().lib;
var test = lib.Test();
test.enrollCallback(printMessage);
try{
test.doCallback(11);
} catch(err) {
console.log(err);
}
在命令行中运行上述代码时,我看不到任何输出。当我运行如下代码: node inspect test.js
并输入继续命令时,调用回调函数时出现以下错误:
When I run the above code in a command line, I don't get any output at all. When I run the code like this: node inspect test.js
and enter the continue command, I get the following error when the callback function is called:
Error: read ECONNRESET
at _errnoException (util.js:992:11)
at TCP.onread (net.js:618:25)
当我逐步执行程序时,控制台出现以下错误:
When I step through my program, I get the following error to the console:
TypeError: test.doCallback is not a function
at Object.<anonymous> (C:\Users\mrcole\Desktop\testy\test.js:22:10)
at Module._compile (module.js:649:14)
at Object.Module._extensions..js (module.js:663:10)
at Module.load (module.js:565:32)
at tryModuleLoad (module.js:505:12)
at Function.Module._load (module.js:497:3)
at Function.Module.runMain (module.js:693:10)
at startup (bootstrap_node.js:191:16)
at bootstrap_node.js:612:3
我在哪里错了,为什么节点行为不一致?
Where am I going wrong, and why is node acting inconsistantly?
推荐答案
要回答我自己的问题,请不要使用nbind以这种方式调用Node JavaScript回调函数。这是一个异步调用(如果我错了,请纠正我),并且截至2018年6月,nbind不支持异步回调。
To answer my own question, don't use nbind for calling a Node JavaScript callback function in this manner. This is an asynchronous call (correct me if I'm wrong) and nbind does not, as of June 2018, support asynchronous callbacks.
一个不错的选择是实现一个提供的 AsyncWorker类。
A good alternative is to implement one of the AsyncWorker classes provided by NAN.
下面是一些示例代码:
class MyAsyncWorker : public Nan::AsyncProgressWorkerBase<T>
{
public:
MyAsyncWorker(Nan::Callback *callback_, const char *resource_name = "My Async Worker")
: AsyncProgressWorkerBase(callback_, resource_name)
{
}
~MyAsyncWorker()
{
}
//Do work, or process notifications here
void Execute(const ExecutionProgress &progress)
{
//do work. when you have something to report,
//call ExecutionProgress::Send( T * data, size_t count) to eventually call
//the HandleProgressCallback function.
}
//Call JavaScript callback from this function
void HandleProgressCallback(T *data, size_t count)
{
Nan::HandleScope scope;
v8::Local<v8::Value> argv[] = {
//initialize your data to passback to callback here
};
callback->Call(count,argv,async_resource);
}
//This is called when you are done executing
virtual void HandleOKCallback()
{
Nan::HandleScope scope;
v8::Local<v8::Value> argv[] = {
//Prepare final values to be returned
};
callback->Call(1,argv,async_resource);
}
};
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