Talking to C++ process through N-API #124

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1. NickNaso commented on Feb 10, 2020

   

   NickNaso

   on Feb 10, 2020

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   Hi @VincentAAX,
   what I understood is that you have two different processes one is a Node.js application and another is a C++ application and you need to pass messages (data) between these two processes to create a sort of IPC communication. In theory you could create a native add-on that that use your dll to exchange / pass data to another process. In the Node.js ecosystem there is an example of this kind of native module that bind the api of ZeroMQ. https://github.com/zeromq/zeromq.js.
2. VincentAAX commented on Feb 11, 2020

   

   VincentAAX

   on Feb 11, 2020

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   Hey Nick;

   I want to communicate to a C++ app in another process and I want to do by shared memory. I believe the zeromq.js does this by sockets. Shared memory is much faster.
3. NickNaso commented on Feb 12, 2020

   

   NickNaso

   on Feb 12, 2020

   Last edited by NickNaso

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   Hi @VincentAAX,
   I don't know how to use the shared memory but in general you could use the ObjectWrap API .
   You could do something like this:

   index.js

   'use strict'
   
   const Shmt = require('YOUR-NATIVE-ADDON')
   
   const opts = {
       name: 'test',
       // ...    
   }
   
   const shmt = new Shmt(opts)
   
   try {
       shmt.open()
       shmt.put(key, value)
       // When you don't need to access shared memory you have to release it
      shmt.close()
   } catch (err) {
       // Handle the error
   }

   shmt.h

   #include <napi.h>
   
   // Include headers that allow you to use the shared memory
   
   class Shmt : public Napi::ObjectWrap<Shmt> {
   
       public:
           static Napi::Object Init(Napi::Env env, Napi::Object exports);
           Shmt(const Napi::CallbackInfo& info);
   
       private:
          // Reference to shared memory
           static Napi::FunctionReference constructor;
           Napi::Value Open(const Napi::CallbackInfo& info);
           Napi::Value Close(const Napi::CallbackInfo& info);
           Napi::Value Get(const Napi::CallbackInfo& info);
           Napi::Value Del(const Napi::CallbackInfo& info);
           Napi::Value Put(const Napi::CallbackInfo& info);     
   };

   shmt.cc

   #include "shmt.h"
   
   Napi::FunctionReference Shmt::constructor;
   Napi::Object Shmt::Init(Napi::Env env, Napi::Object exports) {
       Napi::HandleScope scope(env);
       Napi::Function func = DefineClass(env, "Shmt", {
           InstanceMethod("open", &Shmt::Open),
           InstanceMethod("close", &Shmt::Close),
           InstanceMethod("get", &Shmt::Get),
           InstanceMethod("del", &Shmt::Del),
           InstanceMethod("put", &Shmt::Put)
       });
   
       constructor = Napi::Persistent(func);
       constructor.SuppressDestruct();
   
       exports.Set("Shmt", func);
       return exports;
   }
   
   Shmt::Shmt(const Napi::CallbackInfo& info) 
   : Napi::ObjectWrap<Shmt>(info)  {
       // NOOP
   }
   
   Napi::Value Shmt::Open(const Napi::CallbackInfo& info) {
       Napi::Env env = info.Env();
       // Initialize shared memory
       return info.Env().Undefined();
   }
   
   Napi::Value Shmt::Close(const Napi::CallbackInfo& info) {
       // Release the shared memory
       return info.Env().Undefined();
   }
   
   Napi::Value Shmt::Get(const Napi::CallbackInfo& info) {
      // Get a value from the shared memory
       return info.Env().Undefined();
   }
    
   Napi::Value Shmt::Del(const Napi::CallbackInfo& info) {
      // Remove a value from the shared memory
       return info.Env().Undefined();
   }
   
   Napi::Value Database::Put(const Napi::CallbackInfo& info) {
      // Insert a new value in the shared memory
       return info.Env().Undefined();
   }

   The code is only to give you an idea maybe it contains some errors.