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node.jsshelljs

shelljs performance is slow

I have been using shelljs

On my super fast system I execute this:

var shell = require('shelljs')
const exec = require('child_process').exec

console.time('shell mktemp -d')
shell.exec('mktemp -d', {silent: true})
console.timeEnd('shell mktemp -d')

console.time('child exec mktemp -d')
exec('mktemp', ['-d'], function(error, stdout, stderr) {
  if (error) {
    console.error('stderr', stderr)
    throw error
  }
  console.log('exec stdout', stdout)
  console.timeEnd('child exec mktemp -d')
})

Its giving the following execution times:

shell mktemp -d: 208.126ms

exec stdout /tmp/tmp.w22tyS5Uyu

child exec mktemp -d: 48.812ms

Why is shelljs 4 times slower? Any thoughts?

Solution

  • Have a look to how shelljs is implemented: enter image description here

    It fully relies on node.js fs library. This library is cross platform and written in C++ but not as performant as C language. More generally, you can't have in JS the perfs you get in C...

    Another thing, abstraction layers: you're using exec(Command) where Command is a C tailored (Linux C here I think). The machine creates a thread and executes a command in it. When using shell.js, there are many mechanisms to ensure cross plateform and keep the abstraction of your command as a function and keep the result as a variable. See the code of exec in shell.js: https://github.com/shelljs/shelljs/blob/master/src/exec.js It is not really doing the same thing as your line of code.

    Hope that helps!