child_process: support `Symbol.dispose` #48551

MoLow · 2023-06-25T22:17:18Z

No description provided.

ronag · 2023-06-26T05:39:06Z

lib/internal/child_process.js

@@ -516,6 +520,15 @@ ChildProcess.prototype.kill = function(sig) {
  return false;
 };

+ChildProcess.prototype[SymbolAsyncDispose] = function() {
+  return new Promise((resolve) => {
+    this.on('exit', () => resolve(null));


What if already exited?

What if the user remove all exit event handlers?

ronag

Isn't this changing a little too much? I think this PR could be more minimal.

lib/internal/child_process.js

ronag

I'm unsure whether it's sufficient to wait for 'exit' or 'close' is the more correct event to wait for? Not sure exactly what the difference is between these two.

ronag · 2023-06-26T06:51:24Z

Let's add a closed property to child process and use the following logic:

ChildProcess.prototype[SymbolAsyncDispose] = async function() {
  if (!this.closed) {
    await EE.once(this, 'close');
  }
};

MoLow · 2023-07-02T07:19:40Z

I'm unsure whether it's sufficient to wait for 'exit' or 'close' is the more correct event to wait for? Not sure exactly what the difference is between these two.

according to the code, exit is emitted first when child process exits, then close is fired once all the streams are drained. so we should probably use close

MoLow · 2023-07-02T07:30:47Z

Let's add a closed property to child process and use the following logic:

ChildProcess.prototype[SymbolAsyncDispose] = async function() {
  if (!this.closed) {
    await EE.once(this, 'close');
  }
};

we cannot use EE.once since it will always reject when calling abortChildProcess.

lib/internal/child_process.js

ronag · 2023-07-02T13:14:17Z

lib/internal/child_process.js

+    const ret = this.kill(this[kKillSignal]);
+    assert(ret, 'unexpected kill failure');
+    await EventEmitter.once(this, 'close');
+    this.emit('error', new AbortError());


Why this? Not saying I disagree. Just not sure whether I do agree. @benjamingr any thoughts?

So other consumers of the child process know it was aborted. this is the same behavior we've implemented on Readable[Symbol.asyncDispose]

There is a race here though. The process might still exit successfully.

I am Not sure I follow. can you provide an example?

The process can succeed before it receives the kill. In which case you are emitting a bad error.

An abortion is just a hint. The process may still choose to fully complete.

I think this quickly becomes complicated. I'd prefer not to emit any error here.

it can be a surprising behavior for a child process to exit without a kill signal and a code, and with incomplete stdout/stderr

Let's ask for @ronbuckton 's advice:

The question here is:

await using cp = childProcess1; // someOtherCode doSomethingWith(childProcess1);

What should the behavior be from doSomethingWith's side? For example if someone is reading stdout while another consumer is disposing it should it error?

ronag · 2023-07-02T15:19:06Z

Any signal other than SIGKILL may actually be ignored by the process. Which would lead to a deadlock in our case.

MoLow · 2023-07-02T15:55:34Z

Any signal other than SIGKILL may actually be ignored by the process. Which would lead to a deadlock in our case.

a pending promise is not a deadlock

ronag · 2023-07-02T16:19:28Z

It is if you wait for it, expecting it to resolve and it never does

ronag · 2023-07-02T18:58:45Z

I'd like to have some more opinions on this. I feel there is a risk of this being an anti-pattern that we encourage.

@benjamingr @jasnell

ronag · 2023-07-03T09:13:24Z

Maybe we can get around the deadlock issue by always having a timeout which eventually calls sigkill and makes sure the promise will eventually resolve.

benjamingr · 2023-07-03T17:46:22Z

An alternative is to implement dispose and not asyncDispose, send the signal and wait for nothing. If someone wants to wait for the process to terminate they can do so by listening to the event themselves.

benjamingr · 2023-07-04T11:45:19Z

An alternative is to implement dispose and not asyncDispose, send the signal and wait for nothing. If someone wants to wait for the process to terminate they can do so by listening to the event themselves.

I think this is the only reasonable option given we don't know how to wait for the process to terminate "for sure"

doc/api/child_process.md

nodejs-github-bot · 2023-07-05T03:55:34Z

CI: https://ci.nodejs.org/job/node-test-pull-request/52610/

nodejs-github-bot · 2023-07-05T08:28:45Z

CI: https://ci.nodejs.org/job/node-test-pull-request/52613/

nodejs-github-bot · 2023-07-05T10:21:16Z

Landed in 773fde2

PR-URL: #48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

PR-URL: nodejs#48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

PR-URL: #48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

MoLow requested a review from benjamingr June 25, 2023 22:17

nodejs-github-bot added child_process Issues and PRs related to the child_process subsystem. needs-ci PRs that need a full CI run. labels Jun 25, 2023

MoLow changed the title ~~child_process: support Symbol.asyncDestroy~~ child_process: support Symbol.asyncDispose Jun 26, 2023

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child_process: support Symbol.dispose

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MoLow force-pushed the child-process-destry branch from 0b342e8 to 5d2af02 Compare July 4, 2023 19:43

MoLow changed the title ~~child_process: support Symbol.asyncDispose~~ child_process: support Symbol.dispose Jul 4, 2023

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nodejs-github-bot merged commit 773fde2 into nodejs:main Jul 5, 2023
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juanarbol pushed a commit that referenced this pull request Jul 13, 2023

child_process: support Symbol.dispose

4e08160

PR-URL: #48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

juanarbol mentioned this pull request Jul 13, 2023

V20.5.0 proposal #48761

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Ceres6 pushed a commit to Ceres6/node that referenced this pull request Aug 14, 2023

child_process: support Symbol.dispose

e03039e

PR-URL: nodejs#48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

Ceres6 pushed a commit to Ceres6/node that referenced this pull request Aug 14, 2023

child_process: support Symbol.dispose

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PR-URL: nodejs#48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

ruyadorno pushed a commit that referenced this pull request Sep 11, 2023

child_process: support Symbol.dispose

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PR-URL: #48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

ruyadorno mentioned this pull request Sep 11, 2023

v18.18.0 proposal #49220

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ruyadorno pushed a commit that referenced this pull request Sep 13, 2023

child_process: support Symbol.dispose

535de5a

PR-URL: #48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

ruyadorno pushed a commit that referenced this pull request Sep 17, 2023

child_process: support Symbol.dispose

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PR-URL: #48551 Reviewed-By: Robert Nagy <ronagy@icloud.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

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child_process: support `Symbol.dispose` #48551

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child_process: support Symbol.dispose #48551

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child_process: support `Symbol.dispose` #48551

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