On Thu, May 25, 2017 at 3:33 AM, <[email protected]> wrote:
> Hello everyone,
>
> 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.
>
> Regards, Shahriar
It's right there in the documentation for uv_async_send():
libuv will coalesce calls to :c:func:`uv_async_send`, that is, not
every call to it will
yield an execution of the callback. For example: if
:c:func:`uv_async_send` is called 5
times in a row before the callback is called, the callback will
only be called once. If
:c:func:`uv_async_send` is called again after the callback was
called, it will be called
again.
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