How to spawn a grandchild process for a child process?

问题

I have spawned a child process, below is the code:

const spawn = require('child_process').spawn;
const ls = spawn('ls', ['-lh', '/usr'], { detached: true });

ls.stdout.on('data', (data) => {
  console.log(`stdout: ${data}`);
  fs.writeFileSync('path-to-test.txt', 'stdout');
});

ls.stderr.on('data', (data) => {
  console.log(`stderr: ${data}`);
  fs.writeFileSync('path-to-test.txt', 'stderr');
});

ls.on('close', (code) => {
  console.log(`child process exited with code ${code}`);
});

With option detached: true, it will keep the child process running even the parent process is killed.

My question is: how to run a grandchild process under this child process? Because in my senario, after spawn this child process, the parent process will be killed. So I can't spawn another process, except using existing child process to spawn a grandchild process.

回答1:

First, it's important to note that the detached option only keeps the child alive after the parent dies on a Windows system. In Unix systems, the child will stay alive by default.

In order to spawn a "grandchild process", child_program.js would have to spawn a child process as well. Try this example out to see. Suppose you have app.js which contains the following:

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

const child = spawn(process.argv[0], [__dirname + '/child_program.js'], {
 detached: true,
 stdio: 'ignore'
});

child.unref();

And then suppose, child_program.js contains the following:

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

const child = spawn(process.argv[0], [__dirname + '/grandchild_program.js'], {
 detached: true,
 stdio: 'ignore'
});

child.unref();

And lastly, let's say grandchild_program.js does this:

var fs = require('fs');

fs.writeFileSync(__dirname + '/bob.txt', 'bob was here', 'utf-8');

Create these files, put them in the same directory, run node app.js and then you should see bob.txt show up in that same directory. Let me know if you have any questions. My question to you would be if you know what process.argv[0] gives you and why you're spawning new child processes with that argument.

来源：https://stackoverflow.com/questions/39502355/how-to-spawn-a-grandchild-process-for-a-child-process

标签

node.js

child-process