"exit" process isn't triggered

[qwertypants]

I would like to trigger the "exit" process to run a custom function, however the "exit" never seems to be triggered properly. I used the "SIGINT" event to trigger an "exit" state, however it requires the use of a GPIO library to stop reading GPIO's. This approach seems to work best, however the analogRead function still runs for a few seconds after this is triggered.

var LPD8806 = require('LPD8806-node');  //https://github.com/v0od0oChild/LPD8806-node
var leds = new LPD8806(10, '/dev/spidev1.0');
var gpios = require('gpios'); // https://github.com/v0od0oChild/MuzzleyGalileoDemos/blob/master/lib/gpios.js

var Galileo = require('galileo-io');
var board = new Galileo();

board.analogRead('A0', function(data) {
    console.log(data);
});

board.on('ready', function(){
    leds.fillRGB(255, 0, 0);

    // 'exit' attempt #1: Does not get triggered when closing node server.
//    this.on('exit', function(){
//        console.log('Inside "ready" shutdown');
//        shutDown();
//    });
});

    // 'exit' attempt #2: This also does not get triggered on exit.
//board.on('exit', function(){
//    console.log('Exit outside "ready".');
//    shutDown();
//});

// 'exit' attempt #3 using "SIGINT"
// This does work, however the analogRead still runs a few times after it's triggered
// This also requires a the gpio library to shut everything down.
process.on('SIGINT', function() {
    shutDown();
    gpios.stopReadingGpios();
    gpios.unexportAll(function() {
        process.exit();
    });
});

function shutDown(){
    console.log("Shutting leds down..");
    leds.allOFF();
}

[rwaldron]

All pin interaction must happen after the ready event has been emitted. This won't work reliably and should be completely avoided:

board.analogRead('A0', function(data) {
    console.log(data);
});

board.on('ready', function(){
...

I'm also confused about the additional need for the gpios library—how is that aware of what Galileo-io is doing? How are you triggering SIGINT? Galileo-io's sysfs reading mechanism is bound to process ticks which abide the event loop and cease on exit.

Here is the program I wrote last week when I was trying to repro your issue:

var Galileo = require("galileo-io");
var board = new Galileo();

board.on("ready", function() {
  this.analogRead("A0", function(data) {
    console.log( "A0",  data );
  });

  process.on("exit", function() {
    console.log( "process exiting..." );
  });

  setTimeout(function() {
    process.exit(0);
  }, 2000);
});

Here is your example, reduced to eliminate aspects that Galileo-io has no control over, and corrected to read A0 only after ready is emitted:

var Galileo = require("galileo-io");
var board = new Galileo();

board.on("ready", function() {
  console.log("Ready...");
  board.analogRead("A0", function(data) {
    console.log(data);
  });
});

process.on("SIGINT", function() {
  console.log("Shutting leds down..");
  process.exit(0);
});

Typing Control-C prints "Shutting leds down..." and the program terminates immediately after

[rwaldron]

I figured out why it appeared that the gpios library was effective: it had nothing to do with the library itself, only that it called process.exit();

[rwaldron]

Sidenote

That gpios library is pathologically slow. When I was writing Galileo-io I did filesystem IO performance measurements of writing to GPIOs using various methods, including the exec("echo....") pattern used in gpios; that approach was 42.5x slower than the fastest approach to the same operation.

[qwertypants]

Thanks for the note on the gpio library, I removed it. Here's an updated example that triggers the exit process using the SIGINT event:

var LPD8806 = require('LPD8806-node');
var leds = new LPD8806(10, '/dev/spidev1.0');

var Galileo = require('galileo-io');
var board = new Galileo();

board.on('ready', function(){
    leds.fillRGB(255, 0, 0);
    console.log('Ready...');

    this.analogRead('A0', function(data) {
        console.log(data);
    });

    process.on('exit', function(){
        console.log('process.on("exit")');
        leds.allOFF();
    });
});

process.on('SIGINT', function() {
    console.log('process.on("SIGINT")');
    // Trigger exit process
    process.exit(0);
});

[rwaldron]

I don't have this led device, so can we stick to reduced cases that only involve Galileo-io?

I ran this:

var Galileo = require('galileo-io');
var board = new Galileo();

board.on('ready', function(){
  console.log('Ready...');

  this.analogRead('A0', function(data) {
    console.log(data);
  });

  process.on('exit', function(){
    console.log('process.on("exit")');
  });
});

process.on('SIGINT', function() {
  console.log('process.on("SIGINT")');
  // Trigger exit process
  process.exit(0);
});

Typed "Control-C" and this is the result:

I just pinged @RussTheAerialist about SPI's write/transfer operations—if those are async then you can't call them from within process.on("exit", ...) because there is no event loop turn that will follow.

[qwertypants]

Sounds good (re: -LPD8806).

The last snippet I added gives me my desired result, as your recent code also demonstrates. As long as the "SIGINT" event triggers the process.exit(0) event, then anything in process.on('exit') will be properly executed.

[rwaldron]

Yes, that's correct.