Node JS with node-cmd: wait until execution of prior cmd call is finished

Question

I have a series of python scripts that I want to call via node-cmd in my Node JS application. They rely on each other, so I cannot execute them in parallel. I also cannot use a fixed waiting time, as they always have different execution time. Right now, upon call of my code, all scripts are called at the same time and therefore error... see my code:

pythoncaller: function(req, callback) {

var cmd=require('node-cmd');

cmd.get(`python3 first.py`,
    function(err, data, stderr){
      console.log(err);
      console.log(stderr);
      console.log(data);
});
cmd.get(`python3 second.py`,
    function(err, data, stderr){
      console.log(err);
      console.log(stderr);
      console.log(data);
});

cmd.get(`python3 third.py"`,
    function(err, data, stderr){
      console.log(err);
      console.log(stderr);
      console.log(data);

});
cmd.get(`python3 last.py"`,
    function(err, data, stderr){
      console.log(err);
      console.log(stderr);
      console.log(data);
      callback(data);
});
},

Do you know a solution on how to execute those scripts not in parallel?

Ashish Modi · Accepted Answer · 2020-01-21 09:16:12Z

1

You can Promisify the callback style functions and use .then to execute them one after another. something like this

const cmd = require('node-cmd');
const Promise = require("bluebird");
const getAsync = Promise.promisify(cmd.get, { multiArgs: true, context: cmd });

var cmd = require('node-cmd');

getAsync(`python3 first.py`)
  .then(data => console.log(data))
  .then(() => getAsync(`python3 second.py`)
  .then(data => console.log(data))
  .then(() => getAsync(`python3 third.py"`)
  .then(data => console.log(data))
  .then(() => getAsync(`python3 last.py"`)
  .then(data => console.log(data));

It is also mentioned on node-cmd readme. See here - https://www.npmjs.com/package/node-cmd#with-promises

answered Jan 21, 2020 at 9:16

Ashish Modi

7,8002 gold badges23 silver badges36 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

grodzi · Accepted Answer · 2020-01-21 09:27:46Z

0

According to doc, you may promisify cmd.get.

Alternative to .then with await below

// copy pasted
// either Promise = require('bluebird') or use (require('util').promisify)
const getAsync = Promise.promisify(cmd.get, { multiArgs: true, context: cmd })

pythoncaller: async function(req, callback) {
  try {
    let data
    data = await getAsync(`python3 first.py`)
    data = await getAsync(`python3 second.py`)
    data = await getAsync(`python3 third.py"`)
    // ...
  } catch (e) {
    return callback(e)
  }
  return callback()
}

answered Jan 21, 2020 at 9:27

grodzi

5,7111 gold badge17 silver badges16 bronze badges

Collectives™ on Stack Overflow

Node JS with node-cmd: wait until execution of prior cmd call is finished

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related