Hi again,
Finally, I ended up with this after my experiments to get something back
from js side (which in my case will be a string storing a json object from
a mongodb query result). This way I don't need that many function pointers,
just one for a function that acts as a constructor and by which the js db
handler object gets created:
js_db::js_db(){
mongodb_init_fptr = EM_ASM_INT({
mongodb_init = Runtime.addFunction(function(objid) {
console.log('objid:'+objid);
function mongodb(objid) {
var self = this;
this.id = objid;
this.MongoClient=null;
this.assert=null;
this.init = function () {
console.log('mongoinst init');
self.MongoClient = require('mongodb').MongoClient;
self.assert = require('assert');
};
this.exec_query = function () {
console.log('mongoinst query');
var test = 'test';
var ptr = allocate(intArrayFromString(test),'i8',ALLOC_NORMAL);
return ptr;
};
}
if(typeof mongoinst === 'undefined') {
mongoinst=[];
}
mongoinst[objid] = new mongodb();
mongoinst[objid].init();
});
return mongodb_init;
},0);
void (*mongodb_init)(int) = reinterpret_cast<void
(*)(int)>(mongodb_init_fptr);
mongodb_init(1);//instance number (here: 1) could be handled by the c++
class, not that I'd need more than one instance for a db handler
}
js_db::~js_db(){
//TODO: don't forget Runtime.removeFunction($0);
}
void js_db::exec_query(const std::string& query){
int addr = EM_ASM_INT({
var addr = mongoinst[$0].exec_query();
return addr;
},1);//instance number needs to be passed here as well and TODO: pass in
query as well:)
std::cout<<std::string(reinterpret_cast<char*>(addr))<<std::endl;
}
My question would be now, who manages the memory allocated in the
exec_query() js object method? If I got it right on the wiki, I'd need to
call _free on the js side AND afterwards free() on the c++ side as well. Am
I right?
Thanks®ards,
r0ller
2016. október 10., hétfő 20:24:35 UTC+2 időpontban jj a következőt írta:
>
> These types of activities are best done directly in JS side, with e.g. a
> --js-library myMongoLibrary.js integration, rather than attempting to adapt
> each JS code line to be called from C++ (in a JNI-style fashion). The JS
> libraries allow storing both state and functions on JS side, which makes it
> easier to store database objects and other things that don't need to be
> marshalled over to C++ side, but can be pointed to via using some kind of
> custom opaque handle. See the Emscripten src/library_xxx.js files for
> example usage, they use this facility.
>
> 2016-10-10 17:24 GMT+03:00 <r0l...@freemail.hu <javascript:>>:
>
>> Hi All,
>>
>> I'm trying to instantiate a mongodb client and open it via
>> emscripten::val but I'm already stuck at the beginning:( What I'm trying
>> achieve first, is step 3 of this mongodb doc:
>> https://docs.mongodb.com/getting-started/node/client/ which is this js
>> oneliner: "var MongoClient = require('mongodb').MongoClient;"
>>
>> In the consturctor of my c++ class I have:
>>
>> js_db::js_db(){
>> emscripten::val require = emscripten::val::global("require");
>> emscripten::val mongoModule = require(std::string("mongodb"));
>> emscripten::val mongoClient = mongoModule.MongoClient();
>> //TODO: register objIDs in global objectTracker table;
>> }
>>
>> The error I get is: "no member named 'MongoClient' in 'emscripten::val'
>> ". What am I doing wrong? Why don't I get it in case of mongoModule?
>>
>> What I'd like to achieve then, based on this earlier suggestion of this
>> group (
>> https://groups.google.com/d/msg/emscripten-discuss/7-i5pRK7edQ/-MrCNVAuCAAJ
>> ) is to call mongoClient.connect() like:
>>
>> void js_db::open(const std::string& db_uri){
>> this->db_uri=db_uri;
>> EM_ASM_({
>> var db_uri = Module.Pointer_stringify($0);
>> var mongoClient = objectTracker[$1];
>> //TODO: MongoClient.connect(db_uri, function(err, db)
>> },db_uri.c_str(),mongoClientObjId);
>> }
>>
>> Thanks for any help in advance!
>>
>> Best regards,
>> r0ller
>>
>>
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