gulp task problem - polybuild task was terminated but build files are not there

[duongphuhiep]

var expect = require('gulp-expect-file');
var polybuild = require('polybuild');

gulp.task('gen', function () {
    gulp.src('index.html')
        .pipe(polybuild({maximumCrush: true}))
        .pipe(gulp.dest('_gen/'));

        //Here I expect polybuild was finished and the file index.build.html is ready in my _gen folder; 
       //and here I want to rename it to index.html and put it to my _prod folder

    gulp.src('_gen/index.build.html')
        .pipe(expect('_gen/index.build.html')) //failed! polybuild is not done yet!
        .pipe($.rename('index.html'))
        .pipe(gulp.dest('_prod')); //nothing will be put into the _prod folder
});

Polybuild do the job, but I guess after polybuild, we have to 'sleep' some time to have the index.build.html ready. right? It is a issue for me