如何使用event-stream暂停和恢复Gulp流？

Question

我正在尝试将npm包克隆到客户端位置，因此我创建了多个流来完成此操作，并将它们合并为从gulp.task()返回。然而，据我所知，我需要暂停流，以便任务接收到正确的退出。

下面的代码运行时没有错误，但是如果我注释return行。当我预计没有一个流到达它们的gulp.dest()时，其中一个包仍然被复制。为什么不暂停所有的流？

var gulp = require('gulp')
    , eventStream = require('event-stream')
    ;

const projects = {
    src: {
        dependencies: {
            codemirror: './src/lib/codemirror',
            acorn: './src/lib/acorn'
        }
    }
};

gulp.task('init:client-packages', function () {
    let streams = []
        , ps = eventStream.pause();

    // Load project client-side dependencies
    for (let prj in projects) {
        for (let pkg in projects[prj].dependencies) {
            streams.push(
                gulp.src('./node_modules/' + pkg + '/**')
                    .pipe(ps)
                    .pipe(gulp.dest(projects[prj].dependencies[pkg]))
            );
        }
    }

    // Merge source streams
    return eventStream.merge(streams).pipe(ps.resume());
    // ^^ Commenting this line doesn't block gulp.dest() from completing.
});

Answer 1

由于以下代码仅适用于merge-stream，因此event-stream中可能存在错误。

var merge = require('merge-stream')
    , eventStream = require('event-stream') 
    ;

gulp.task('init:client-packages', function() {
    let streams = [];

    // Load project client-side dependencies
    for (let prj in projects) {
        for (let pkg in projects[prj].dependencies) {
            streams.push(
                gulp.src('./node_modules/' + pkg + '/**')
                    .pipe(gulp.dest(projects[prj].dependencies[pkg]))
            );
        }
    }

    // Merge source streams
    return merge(streams);
    // --OR--
    return eventStream.merge(streams); // Results in message below.
});

如上所述，event-stream没有正确关闭任务。输出如下：

[23:36:46] Starting 'init:client-packages'...
[23:36:47] The following tasks did not complete: init:client-packages
[23:36:47] Did you forget to signal async completion?
Process terminated with code 1.