Gulp running dependencies in parallel

[LandonSchropp]

I'm trying to write a simple build system with Gulp. I'm using Gulp 3.8.7. Here's my gulpfile.js:

var gulp = require('gulp');
var clean = require('gulp-clean');
var sass = require('gulp-ruby-sass');
var autoprefixer = require('gulp-autoprefixer');
var minifyCSS = require('gulp-minify-css');
var rename = require("gulp-rename");

gulp.task('clean', function() {
  return gulp.src('build/**/*', {read: false})
    .pipe(clean());
});

gulp.task('compile', function() {
  return gulp.src('source/griddle.sass')
    .pipe(sass({style: 'expanded', lineNumbers: true}))
    .pipe(autoprefixer('last 2 versions', '> 1%', 'ie >= 10'))
    .on('error', function (err) { console.log(err.message); })
    .pipe(gulp.dest('build'));
});

gulp.task('minify', function() {
  return gulp.src('build/griddle.css')
    .pipe(minifyCSS())
    .pipe(rename("griddle.min.css"))
    .on('error', function (err) { console.log(err.message); })
    .pipe(gulp.dest('build'));
});

gulp.task('default', [ 'clean', 'compile', 'minify' ]);

Every other time I run gulp, I get the following error:

[14:11:19] Using gulpfile ~/Development/griddle/gulpfile.js
[14:11:19] Starting 'clean'...
[14:11:19] Starting 'build'...
[14:11:19] Starting 'minify'...
[14:11:19] Finished 'clean' after 23 ms

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: ENOENT, open '/Users/landonschropp/Development/griddle/build/griddle.css'

It looks like Gulp is running clean, compile and minify in parallel, even though the tasks are dependent. Am I missing something?

[pkozlowski-opensource]

Nope, you are right, all the deps are run in parallel which is desirable in most cases to maximise performance. Still, there are cases where the very nature of tasks calls for serial execution. There are some work-arounds to achieve this in the current version of gulp (https://www.npmjs.org/package/run-sequence) but it is something that is going to be handled very elegantly in Gulp 4, see #355

[mallowigi]

This is because gulp run in maximum concurrency, so you cannot be sure that minify run once and only after clean and build.

This should be fixed in the runSeries improvement of gulp 4, but for the time being, you should take a look at run-sequence (https://www.npmjs.org/package/run-sequence)

[LandonSchropp]

Ah, I see. Thanks for the lightning fast replies!