Add killDescendants option to also terminate descendant processes

Fixes #96

Author: sindresorhus

docs/api.md

@@ -1168,6 +1168,21 @@ Kill the subprocess when the current process exits.
 
 [More info.](termination.md#current-process-exit)
 
+### options.killDescendants
+
+_Type:_ `boolean`\
+_Default:_ `false`
+
+When the subprocess is terminated by Execa, also terminate all of its descendant processes, instead of only the subprocess itself.
+
+This is useful when the subprocess spawns its own processes, such as when using the [`shell`](#optionsshell) option.
+
+On Unix, this spawns the subprocess in its own [process group](https://en.wikipedia.org/wiki/Process_group). On Windows, this uses [`taskkill`](https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/taskkill).
+
+This is best-effort: descendant processes that create their own process group or session are not terminated.
+
+[More info.](termination.md#killing-descendant-processes)
+
 ### options.uid
 
 _Type:_ `number`\

docs/termination.md

@@ -192,7 +192,26 @@ If the current process exits, the subprocess is automatically [terminated](#defa
 - The subprocess is run in the background using the [`detached`](api.md#optionsdetached) option.
 - The current process was terminated abruptly, for example, with [`SIGKILL`](#sigkill) as opposed to [`SIGTERM`](#sigterm) or a successful exit.
 
-On Windows, only the subprocess is terminated, not the other processes it might have spawned. To also terminate those, the [`windowsHide: false`](windows.md#console-window) option can be used.
+By default, only the subprocess is terminated, not the other processes it might have spawned. The [`killDescendants`](#killing-descendant-processes) option can be used to also terminate those.
+
+## Killing descendant processes
+
+By default, [terminating](#signal-termination) a subprocess only sends a signal to that subprocess, not to any process it might have spawned itself. For example, terminating a subprocess started with the [`shell`](api.md#optionsshell) option only terminates the shell, not the command it is running.
+
+The [`killDescendants`](api.md#optionskilldescendants) option terminates the whole process tree instead: the subprocess and all of its descendants. This applies to every way Execa terminates a subprocess, including [`subprocess.kill()`](#signal-termination), the [`cancelSignal`](#canceling), [`timeout`](#timeout), [`maxBuffer`](output.md#big-output) and [`cleanup`](#current-process-exit) options, and the [`forceKillAfterDelay`](#forceful-termination) escalation.
+
+```js
+// Without `killDescendants`, only the shell is terminated, and `sleep` keeps running
+const subprocess = execa({shell: true, killDescendants: true})`sleep 60`;
+subprocess.kill();
+await subprocess;
+```
+
+On Unix, this spawns the subprocess in its own [process group](https://en.wikipedia.org/wiki/Process_group), then sends the signal to that group. On Windows, this uses [`taskkill`](https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/taskkill), which terminates the process tree tracked by the OS.
+
+This is best-effort. On Unix, descendant processes that create their own process group or session (for example, daemons calling [`setsid()`](https://man7.org/linux/man-pages/man2/setsid.2.html)) escape termination. On Unix, because the subprocess runs in its own process group, it is also detached from the terminal, so pressing `CTRL-C` no longer forwards [`SIGINT`](#sigint) to it.
+
+This option cannot be used with [synchronous methods](execution.md#synchronous-execution).
 
 ## Signal termination
 

lib/arguments/options.js

@@ -54,6 +54,7 @@ const addDefaultOptions = ({
 	encoding = 'utf8',
 	reject = true,
 	cleanup = true,
+	killDescendants = false,
 	all = false,
 	windowsHide = true,
 	killSignal = 'SIGTERM',
@@ -73,6 +74,7 @@ const addDefaultOptions = ({
 	encoding,
 	reject,
 	cleanup,
+	killDescendants,
 	all,
 	windowsHide,
 	killSignal,

lib/methods/main-async.js

@@ -14,6 +14,7 @@ import {handleStdioAsync} from '../stdio/handle-async.js';
 import {stripNewline} from '../io/strip-newline.js';
 import {pipeOutputAsync} from '../io/output-async.js';
 import {subprocessKill} from '../terminate/kill.js';
+import {getSpawnOptions, getKillFunction} from '../terminate/kill-descendants.js';
 import {cleanupOnExit} from '../terminate/cleanup.js';
 import {pipeToSubprocess} from '../pipe/setup.js';
 import {makeAllStream} from '../resolve/all-async.js';
@@ -84,7 +85,7 @@ const handleAsyncOptions = ({timeout, signal, ...options}) => {
 const spawnSubprocessAsync = ({file, commandArguments, options, startTime, verboseInfo, command, escapedCommand, fileDescriptors}) => {
 	let subprocess;
 	try {
-		subprocess = spawn(...concatenateShell(file, commandArguments, options));
+		subprocess = spawn(...concatenateShell(file, commandArguments, getSpawnOptions(options)));
 	} catch (error) {
 		return handleEarlyError({
 			error,
@@ -107,7 +108,7 @@ const spawnSubprocessAsync = ({file, commandArguments, options, startTime, verbo
 	const context = {};
 	const onInternalError = createDeferred();
 	const kill = subprocessKill.bind(undefined, {
-		kill: subprocess.kill.bind(subprocess),
+		kill: getKillFunction(subprocess, options),
 		options,
 		onInternalError,
 		context,

lib/methods/main-sync.js

@@ -51,7 +51,7 @@ const handleSyncArguments = (rawFile, rawArguments, rawOptions) => {
 const normalizeSyncOptions = options => options.node && !options.ipc ? {...options, ipc: false} : options;
 
 // Options validation logic specific to sync methods
-const validateSyncOptions = ({ipc, ipcInput, detached, cancelSignal}) => {
+const validateSyncOptions = ({ipc, ipcInput, detached, cancelSignal, killDescendants}) => {
 	if (ipcInput) {
 		throwInvalidSyncOption('ipcInput');
 	}
@@ -64,6 +64,10 @@ const validateSyncOptions = ({ipc, ipcInput, detached, cancelSignal}) => {
 		throwInvalidSyncOption('detached: true');
 	}
 
+	if (killDescendants) {
+		throwInvalidSyncOption('killDescendants: true');
+	}
+
 	if (cancelSignal) {
 		throwInvalidSyncOption('cancelSignal');
 	}

lib/terminate/kill-descendants.js

@@ -0,0 +1,54 @@
+import process from 'node:process';
+import {execFile} from 'node:child_process';
+
+const isWindows = process.platform === 'win32';
+
+// The `killDescendants` option terminates the whole process tree, not just the direct child.
+// On Unix, this requires spawning the subprocess in its own process group, so we override the
+// `detached` argument passed to `child_process.spawn()`.
+// This is kept separate from the user-facing `detached` option, which must keep its own value,
+// so the `cleanup` behavior is not affected.
+export const getSpawnOptions = options => options.killDescendants && !isWindows
+	? {...options, detached: true}
+	: options;
+
+// Returns the low-level function used to send a signal to the subprocess.
+// With the `killDescendants` option, the signal is sent to the whole process tree.
+export const getKillFunction = (subprocess, {killDescendants}) => {
+	if (!killDescendants) {
+		return subprocess.kill.bind(subprocess);
+	}
+
+	const killDescendantsFunction = isWindows ? killDescendantsWindows : killDescendantsUnix;
+	return killDescendantsFunction.bind(undefined, subprocess);
+};
+
+// On Unix, the subprocess is its own process group leader (its PGID equals its PID), since it
+// was spawned with `detached: true`. Sending the signal to `-pid` targets the whole group.
+const killDescendantsUnix = (subprocess, signal) => {
+	if (subprocess.pid === undefined) {
+		return false;
+	}
+
+	try {
+		return process.kill(-subprocess.pid, signal);
+	} catch {
+		// The process group might already be gone, or signaling it might not be permitted, so we
+		// fall back to the direct child. Like `ChildProcess.kill()`, this returns `false` instead of throwing.
+		return subprocess.kill(signal);
+	}
+};
+
+// Windows has no process groups. Instead, `taskkill /T` recursively terminates the process tree.
+// It must run while the tree is still intact, so it is the only termination performed: killing the
+// direct subprocess first would orphan its descendants before `taskkill` could enumerate them.
+// Windows does not support signals, so the signal argument is ignored (`/F` terminates the tree).
+const killDescendantsWindows = subprocess => {
+	if (subprocess.pid === undefined) {
+		return false;
+	}
+
+	// This is best-effort: any error (such as the subprocess having already exited) is ignored.
+	execFile('taskkill', ['/pid', `${subprocess.pid}`, '/T', '/F'], () => {});
+	return true;
+};

test-d/arguments/options.test-d.ts

@@ -275,6 +275,13 @@ expectError(execaSync('unicorns', {detached: true as boolean}));
 expectError(await execa('unicorns', {detached: 'true'}));
 expectError(execaSync('unicorns', {detached: 'true'}));
 
+await execa('unicorns', {killDescendants: true});
+expectError(execaSync('unicorns', {killDescendants: true}));
+await execa('unicorns', {killDescendants: true as boolean});
+expectError(execaSync('unicorns', {killDescendants: true as boolean}));
+expectError(await execa('unicorns', {killDescendants: 'true'}));
+expectError(execaSync('unicorns', {killDescendants: 'true'}));
+
 await execa('unicorns', {cancelSignal: AbortSignal.abort()});
 expectError(execaSync('unicorns', {cancelSignal: AbortSignal.abort()}));
 expectError(await execa('unicorns', {cancelSignal: false}));

test/terminate/kill-descendants.js

@@ -0,0 +1,86 @@
+import process from 'node:process';
+import {setTimeout} from 'node:timers/promises';
+import test from 'ava';
+import isRunning from 'is-running';
+import {execa, execaSync} from '../../index.js';
+import {setFixtureDirectory} from '../helpers/fixtures-directory.js';
+
+setFixtureDirectory();
+
+const isWindows = process.platform === 'win32';
+
+const pollForSubprocessExit = async pid => {
+	while (isRunning(pid)) {
+		// eslint-disable-next-line no-await-in-loop
+		await setTimeout(100);
+	}
+};
+
+// `ipc-send-pid.js` spawns a descendant process (`forever.js`) and sends back its PID.
+const spawnDescendant = async (killDescendants, options) => {
+	const subprocess = execa('ipc-send-pid.js', ['false', 'false'], {stdio: 'ignore', ipc: true, killDescendants, ...options});
+	const descendantPid = await subprocess.getOneMessage();
+	return {subprocess, descendantPid};
+};
+
+test('killDescendants terminates descendant processes', async t => {
+	const {subprocess, descendantPid} = await spawnDescendant(true);
+	t.true(isRunning(descendantPid));
+
+	subprocess.kill();
+	await t.throwsAsync(subprocess);
+	t.false(isRunning(subprocess.pid));
+
+	await Promise.race([
+		setTimeout(1e4, undefined, {ref: false}),
+		pollForSubprocessExit(descendantPid),
+	]);
+	t.false(isRunning(descendantPid));
+});
+
+test('killDescendants also terminates descendant processes when the subprocess times out', async t => {
+	const {subprocess, descendantPid} = await spawnDescendant(true, {timeout: 1_000});
+	t.true(isRunning(descendantPid));
+
+	const {isTerminated, timedOut} = await t.throwsAsync(subprocess);
+	t.true(isTerminated);
+	t.true(timedOut);
+
+	await Promise.race([
+		setTimeout(1e4, undefined, {ref: false}),
+		pollForSubprocessExit(descendantPid),
+	]);
+	t.false(isRunning(descendantPid));
+});
+
+// On Windows, terminating the direct subprocess already terminates its descendants, so this
+// only asserts the default Unix behavior of leaving descendants running.
+if (!isWindows) {
+	test('descendant processes are not terminated without killDescendants', async t => {
+		const {subprocess, descendantPid} = await spawnDescendant(false);
+		t.true(isRunning(descendantPid));
+
+		subprocess.kill();
+		await t.throwsAsync(subprocess);
+		t.false(isRunning(subprocess.pid));
+
+		t.true(isRunning(descendantPid));
+		process.kill(descendantPid, 'SIGKILL');
+	});
+
+	test('timeout does not terminate descendants without killDescendants', async t => {
+		const {subprocess, descendantPid} = await spawnDescendant(false, {timeout: 1_000});
+		t.true(isRunning(descendantPid));
+
+		const {timedOut} = await t.throwsAsync(subprocess);
+		t.true(timedOut);
+		t.true(isRunning(descendantPid));
+		process.kill(descendantPid, 'SIGKILL');
+	});
+}
+
+test('Cannot use "killDescendants" option, sync', t => {
+	t.throws(() => {
+		execaSync('empty.js', {killDescendants: true});
+	}, {message: /The "killDescendants: true" option cannot be used/});
+});

types/arguments/options.d.ts

@@ -329,6 +329,19 @@ export type CommonOptions<
 	*/
 	readonly cleanup?: Unless<IsSync, boolean>;
 
+	/**
+	When the subprocess is terminated by Execa, also terminate all of its descendant processes, instead of only the subprocess itself.
+
+	This is useful when the subprocess spawns its own processes, such as when using the `shell` option.
+
+	On Unix, this spawns the subprocess in its own [process group](https://en.wikipedia.org/wiki/Process_group). On Windows, this uses [`taskkill`](https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/taskkill).
+
+	This is best-effort: descendant processes that create their own process group or session are not terminated.
+
+	@default false
+	*/
+	readonly killDescendants?: Unless<IsSync, boolean>;
+
 	/**
 	Sets the [user identifier](https://en.wikipedia.org/wiki/User_identifier) of the subprocess.