在node.js中運行串行操作

Question

我有一個異步函數，可以並行執行一些shell命令

require("fs").readdir("./", function (error, folders) { // asynched
    require("underscore")._(folders).each(function (folder, folderKey, folderList) { // asynched
    r("child_process").exec("ls ./" + folder, function(error, stdout, stderr) {
           console.log("Cant put it here") // Will be run after the first execution is completed
        })
        console.log("Cant put it here either") // Will be run immediately before any execution is completed
    })
    console.log("Cant put it here either") // Will be run immediately before any execution is completed
})

我想在執行完這些shell命令后做一些事情，但是我無法弄清楚如何使用異步庫做到這一點。 這些shell命令是並行執行的，因此無法注冊在所有命令執行后執行的處理程序。

有任何想法嗎？

Answer 1

使用async.js庫： https : //github.com/caolan/async

var fs = require('fs');
var async = require('async');
var exec = require('child_process').exec;

fs.readdir("./", function (error, folders) {
    async.forEach(folders, function (folder, callback) {
        exec("ls ./" + folder, function (error, stdout, stderr) {
            callback();
        });
    },
    function (error) {
        // this is called after all shell commands are complete
    })
});

Answer 2

更新資料

在您編輯問題以顯示您的實際代碼之后，這應該可以工作：

var ps = require('child_process');
var fs = require('fs');
var _ = require("underscore");

function listDirectory(dir, callback) {
    fs.readdir(dir, function (error, folders) {

        // simply keep track on how many of the ls's have finished
        var count = folders.length, done = 0;
        _(folders).each(function (folder, folderKey, folderList) {
            ps.exec("ls ./" + folder, function(error, stdout, stderr) {
                console.log('one more done');
                done++;
                if (done === count) {
                    callback();
                } 
            });  
        });
    })
}

listDirectory('./', function() {
    console.log('all done!');
});

運行時：

one more done
one more done
one more done
one more done
one more done
one more done
one more done
one more done
one more done
one more done
one more done
one more done
all done!

舊答案

我想您使用child_process模塊。

您需要圍繞命令創建包裝器。

var spawn = require('child_process').spawn;


// this function will execute all the things in the cmds array
// after all the processes have exited, it will call the callback
function multiSpawn(cmds, callback) {
    var count = cmds.length;
    var done = 0;
    for(var i = 0; i < count; i++) {
        // spawn the process, modify this if you need to hook up further events
        // you could also pass in further functions to setup each spawn

        var ps = spawn(cmds[i].shift(), cmds[i]);
        ps.on('exit', function() {
            done++; // keep track on how many commands have finished
            if (done === count) {
                callback();
            } 
        });
    }
}

multiSpawn([
    ['ls', '/usr/lib', '-l'],
    ['sleep', '1'], // this will sleep 1 seconds
    ['ls', '/usr/share', '-a']

], function() {
    console.log('all done');
});

這將運行所有3個命令，兩個ls將立即完成，在調用回調之后， sleep將使所有內容延遲1秒。

我想使用Futures也是可能的，但是在這種情況下，這很可能是過大了。