Emscripten Javascript接口实现 [英] Emscripten Javascript interface implementation
问题描述
我需要更多的信息,如何在javascript中实现emscripten生成的类。我在c ++中有以下界面,但需要在javascript端实现它。
I need a bit more information on how to implement emscripten generated classes in javascript. I have the following interface in c++ but need to implement it on the javascript side.
class OsHttp {
public:
virtual ~OsHttp() {}
virtual void request(const std::string & verb, const std::string & url, const std::string & body, const std::unordered_map<std::string, std::string> & headers, const std::shared_ptr<HttpCallback> & callback) = 0;
};
我知道以下会让我开始,但是如何实现构造函数等。 p>
I know that the following will get me started, but how do i implement the constructor etc.
var osHttp = {
constructor: function(){}
request: function(verb, url, body, headers, callback) {
console.log('OsHttp with: ' + verb);
}
};
var OsHttpObject = Module.OsHttp.implement(osHttp);
推荐答案
如果我明白你在做什么,那么你需要有一些方式在Javascript和C ++世界之间进行通信。另外,我认为如果你想使用一个实现这个接口在C ++中的对象,然后让它编译和运行,必须有一个具体的实现接口的C ++。这个接口的实现将调用Javascript。
If I'm understanding what you're after, then you need to have some way of communicating between the Javascript and C++ worlds. Also, I think that if you want to use an object that implements this interface in C++, then to get it to compile and run, there must be a concrete implementation of the interface in C++. This implementation of the interface would then call out to Javascript.
为了做到这一点,你可以使用 EM_ASM_ * macros 在实现接口的类中:
To do this, you could use the EM_ASM_* macros in a class that implements the interface:
class OsHttpImplementation : public OsHttp {
public:
~OsHttp()
{
EM_ASM({
// Cleanup anything in Javascript context
});
}
void request(const std::string & verb, const std::string & url, const std::string & body, const std::unordered_map<std::string, std::string> & headers, const std::shared_ptr<HttpCallback> & callback)
{
// Probably a good idea to save any shared pointers as members in C++
// so the objects they point to survive as long as you need them
int returnValue = EM_ASM_INT_V({
// Example ways of accessing data from C++
var verb = Pointer_stringify($0);
var url = Pointer_stringify($1);
var body = Pointer_stringify($2);
var callbackFunctionPointer = $3;
// Something here that makes an HTTP request, creates any objects, etc.
return 0;
}, verb.c_str(), url.c_str(), body.c_str(), callback.get());
}
};
如果你希望实际上是对应于C ++对象的Javascript对象,做一些手动管理在Javascript中创建/存储/删除对象在某种工厂。具体来说,它需要将它们存储在某个地方,以便C ++可以通过某种键访问正确的。指向this的指针可以方便地:
If you want there to actually be an object in Javascript that corresponds to the C++ object, you might have to do a bit of manual management in Javascript to create/store/delete objects in some sort of factory. Specifically, it would need to store them somewhere so the C++ can access the right one via some sort of key. The pointer to "this" could be handy for that:
class OsHttpImplementation : public OsHttp {
public:
OsHttp()
{
EM_ASM_V({
var thisPointer = $0;
OsHttpFactory.construct(thisPointer);
}, this);
}
~OsHttp()
{
EM_ASM({
var thisPointer = $0;
OsHttpFactory.destruct(thisPointer);
}, this);
}
void request(const std::string & verb, const std::string & url, const std::string & body, const std::unordered_map<std::string, std::string> & headers, const std::shared_ptr<HttpCallback> & callback)
{
int returnValue = EM_ASM_INT_V({
var thisPointer = $0;
OsHttpFactory.get(thisPointer).request($1, $2, $3, $4);
}, this, verb.c_str(), url.c_str(), body.c_str(), callback.get());
}
};
您在Javascript中实现OsHttpFactory有很多自由。你没有提到在浏览器中是否需要这样做,但是如果你使用XMLHttpRequests,你可以使用
You have a lot of freedom on the implementation of OsHttpFactory in Javascript. You haven't mentioned if you want this in a browser, but if you do, and are using XMLHttpRequests, you could have something like
(function(context) {
var store = {}
function OsHttp() {
this.request = null;
}
OsHttp.prototype.request = function(verb, url, body, callbackPointer) {
var request = this.request = new XMLHttpRequest();
request.onreadystatechange = function() {
if (request.readyState == 4) {
// Might need other arguments if you want to pass something back to C++
Module.Runtime.dynCall('v', callbackPointer, []);
}
});
this.request.open(verb, url, true);
this.request.send();
};
OsHttp.prototype.cleanup = function() {
// Do something to cleanup in-progress requests etc.
}
context.OsHttpFactory = {
construct: function(thisPointer) {
store[thisPointer] = new OsHttp();
},
destruct: function(thisPointer) {
store[thisPointer].cleanup();
delete store[thisPointer];
},
get: function(thisPointer) {
return store[thisPointer];
}
};
})(window);
然后在C ++中你可以使用它作为一个标准类:
Then in C++ you could use it as a standard class:
// Run constructors
auto osHttp = new OsHttpImplementation();
// Make request
osHttp->request(....);
// Run destructors, and remove object from the Javascript store
delete osHttp;
我不得不说,这是一个faff!
I have to say, it's all a bit of a faff!
这篇关于Emscripten Javascript接口实现的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!