等待CasperJS中的子进程 [英] Wait for a child process in CasperJS

问题描述

我有一个加载某些页面的CasperJS进程，然后需要调用go-process来分析页面并决定接下来要加载哪个页面。 go-process需要一段时间才能执行。我的问题是CasperJS不会等待go-process完成并退出。

I have a CasperJS process that loads some page and then it needs to call a go-process to analyze the page and to decide what page should be loaded next. go-process takes a while to execute. My problem is that CasperJS doesn't wait for the go-process to complete and exits.

casper.then(function(){
  var p = cp.execFile('/path/parse', [], {}, function(error, stdout, stderr) {
    console.log(stdout);
  });

});

我如何等待子进程完成？

How can I wait for my child process to complete?

推荐答案

所有然后* 和等待* 函数正在安排要执行的步骤。当CasperJS用完执行步骤并且没有函数传递到 casper.run（）时，它将自动退出。

All then* and wait* functions are scheduling steps to be executed. When CasperJS runs out of steps to execute and no function is passed into casper.run(), then it will automatically exit.

简单的解决方法是始终将空函数传递给 casper.run（）并从函数内部安排新步骤：

The easy fix would be to always pass an empty function into casper.run() and schedule new steps from inside the function:

casper.then(function(){
  var p = cp.execFile('/path/parse', [], {}, function(error, stdout, stderr) {
    console.log(stdout);
    casper.thenOpen(parsedUrl).then(function(){
      // do something on page
    });
  });
});
casper.run(function(){});

更简洁的方法是编写自己的步骤函数来包装 execFile function：

A more clean approach would be to write your own step function that wraps the execFile function:

casper.waitForFileExec = function(process, callback, onTimeout, timeout){
    this.then(function(){
        var cp = require('child_process'),
            finished = false,
            self = this;
        timeout = timeout === null || this.options.stepTimeout;
        cp.execFile(process, [], {}, function(error, stdout, stderr) {
            finished = true;
            callback.call(self, error, stdout, stderr);
        });
        this.waitFor(function check(){
            return finished;
        }, null, onTimeout, timeout);
    });
    return this; // for builder/promise pattern
};

...
casper.waitForFileExec('/path/parse', function(error, stdout, stderr) {
    this.echo(stdout);
    this.thenOpen(parsedUrl).then(function(){
        // do something on page
    });
}).run();

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