Deno.run executes some programs immediately but others

[sant123]

Hi, please take a look at this code:

// mod.ts
const p1 = Deno.run({
  cmd: ['echo', 'deno'],
});

const p2 = Deno.run({
  cmd: ['deno', 'run', 'child.ts'],
});

// p2.status();

// child.ts
console.log('Hi from child!');

If running this code with deno run --allow-run mod.ts it will print in stdout deno.

Now comment out p2.status(); and run it again:

// mod.ts
const p1 = Deno.run({
  cmd: ['echo', 'deno'],
});

const p2 = Deno.run({
  cmd: ['deno', 'run', 'child.ts'],
});

p2.status();

Now prints both deno and Hi from child!.

My question is, is this expected behavior? If it is please some one can explain me why this happens?

Thank you so much.

Deno v1.13.0

[littledivy]

Deno.run won't wait for the process to complete and will exit. The first process was too short lived that you could see the output before Deno exited. When you add p.status(), it returns a new Promise that will resolve when the process returns a status code.

[sant123]

So in theory the second process just runs and exit? I tried to write a file in the second process but didn't work either. It's like the second process never gets executed.

[nayeemrmn]

Deno.run won't wait for the process to complete and will exit. The first process was too short lived that you could see the output before Deno exited. When you add p.status(), it returns a new Promise that will resolve when the process returns a status code.

@littledivy This seems buggy, Deno.run() should dispatch some kind of async op that leaves the process alive right? But I wonder why this doesn't happen with Deno.spawnChild()...

[lucacasonato]

@nayeemrmn With Deno.run the process will only wait if you call p.status(). With Deno.spawnChild this happens automatically, and the promise is available on Child#status

[nayeemrmn]

@nayeemrmn With Deno.run the process will only wait if you call p.status(). With Deno.spawnChild this happens automatically, and the promise is available on Child#status

Ah, we prevent it from closing stdin in that case with stdin.take(). So shouldn't we do the exact same thing with Deno.run()? And manually close it in process.status() to preserve the current anti-deadlock behaviour (which Deno.spawnChild() doesn't have).

[sant123]

This is solved by Deno.spawn:

const p1 = await Deno.spawn("echo", {
  args: ["deno"],
  stdout: "inherit",
});

const p2 = await Deno.spawn("deno", {
  args: ["run", "child.ts"],
  stdout: "inherit",
});