nodejs addon async callback with libuv

I have a node js service that calls into a native C library. The native library, fire events repeatedly and continuously. These events are delivered to a C callback function. My goal is to call a Javascript callback from this native C callback.

Based on my reading, I am using uv_async_init and uv_async_send to accomplish this goal.

The problem I am encountering is that my native C callback function gets called many times and in there uv_async_send is called many times, but the function passed to uv_async_init is called only once and only when my program exits.

Here is my C code:

=====================================================

#include "jsaudio.h"
#include <iostream>

using namespace v8;

static void recordAudioCallback(int index);
void asyncmsg(uv_async_t* handle);
Callback* cbPeriodic;
uv_async_t async;
uv_loop_t* loop;

NAN_METHOD(createEngine) {
    std::cout << "==> createEngine\n" ;
}

void createAudioRecorder(const Nan::FunctionCallbackInfo<v8::Value>& info) {
    std::cout << "==> createAudioRecorder\n";
}

void startRecording(const Nan::FunctionCallbackInfo<v8::Value>& info) {
    std::cout << "==> startRecording\n";
    cbPeriodic = new Callback(info[0].As<Function>());
    loop = uv_default_loop();
    uv_async_init(loop, &async, asyncmsg);
}

void asyncmsg(uv_async_t* handle) {
  std::cout << "==> asyncmsg \n";
  Nan::HandleScope scope;
  v8::Isolate* isolate = v8::Isolate::GetCurrent();
  Local<Value> argv[] = { v8::String::NewFromUtf8(isolate, "Hello world") };
  cbPeriodic->Call(1, argv);
}

/* This my callback that gets called many times, by a native library*/
static void recordAudioCallback(int index) {
  std::cout << "==> recordAudioCallback " << index << "\n";
  uv_async_send(&async);
}

======================================================

Here is my test node.js code that calls the above native code

const jsAudio = new JsAudio({sampleRate: 48000, bufferSize: 8192})

function Test () {
  jsAudio.createEngine();

  jsAudio.createAudioRecorder();

  jsAudio.startRecording(function(error, result) {
    if (error) {
      console.log('startRecording failed: ' + error);
    } else {
      console.log('startRecording result: ' + result);
    }
  });
}

Test();

var waitTill = new Date(new Date().getTime() + 3 * 1000);
while(waitTill > new Date()){}

jsAudio.shutdown();

console.log('program exit...');

==========================================================

Here is the out:

==> createEngine
==> createAudioRecorder
==> startRecording
==> recordAudioCallback 0
==> recordAudioCallback 1
==> recordAudioCallback 0
==> recordAudioCallback 1
==> recordAudioCallback 0
==> shutdown
program exit...
==> asyncmsg 
startRecording failed: Hello world

===========================================================

Why asyncmsg is called only once! even though recordAudioCallback is called several times! Any why is it called after program exits!

Any help is appreciated.

via S. Vaghar