灵活的并行和串联混合可在node.js中使用

Question

操作手册中来自node.js的代码示例：

var flow = require('nimble');
var exec = require('child_process').exec;

function downloadNodeVersion(version, destination, callback) {
  var url = 'http://nodejs.org/dist/node-v' + version + '.tar.gz';
  var filepath = destination + '/' + version + '.tgz';
  exec('curl ' + url + ' >' + filepath, callback);
}

flow.series([
  function (callback) {
    flow.parallel([
      function (callback) {
        console.log('Downloading Node v0.4.6...');
        downloadNodeVersion('0.4.6', '/tmp', callback);
      },
      function (callback) {
        console.log('Downloading Node v0.4.7...');
        downloadNodeVersion('0.4.7', '/tmp', callback);
      }
    ], callback);
  },
  function(callback) {
    console.log('Creating archive of downloaded files...');
    exec(
      'tar cvf node_distros.tar /tmp/0.4.6.tgz /tmp/0.4.7.tgz',
      function(error, stdout, stderr) {
        console.log('All done!');
        callback();
      }
    );
  }
]);

但是flow.series中的第二个函数（回调）未执行，即未创建最终的.tar存档。 怎么了？

Answer 1

它在exec（）块中-因此上下文丢失。