138 lines
5.3 KiB
Markdown
138 lines
5.3 KiB
Markdown
# utilityProcess
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`utilityProcess` creates a child process with
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Node.js and Message ports enabled. It provides the equivalent of [`child_process.fork`][] API from Node.js
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but instead uses [Services API][] from Chromium to launch the child process.
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Process: [Main](../glossary.md#main-process)<br />
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## Methods
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### `utilityProcess.fork(modulePath[, args][, options])`
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* `modulePath` string - Path to the script that should run as entrypoint in the child process.
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* `args` string[] (optional) - List of string arguments that will be available as `process.argv`
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in the child process.
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* `options` Object (optional)
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* `env` Object (optional) - Environment key-value pairs. Default is `process.env`.
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* `execArgv` string[] (optional) - List of string arguments passed to the executable.
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* `cwd` string (optional) - Current working directory of the child process.
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* `stdio` (string[] | string) (optional) - Allows configuring the mode for `stdout` and `stderr`
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of the child process. Default is `inherit`.
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String value can be one of `pipe`, `ignore`, `inherit`, for more details on these values you can refer to
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[stdio][] documentation from Node.js. Currently this option only supports configuring `stdout` and
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`stderr` to either `pipe`, `inherit` or `ignore`. Configuring `stdin` is not supported; `stdin` will
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always be ignored.
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For example, the supported values will be processed as following:
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* `pipe`: equivalent to ['ignore', 'pipe', 'pipe'] (the default)
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* `ignore`: equivalent to 'ignore', 'ignore', 'ignore']
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* `inherit`: equivalent to ['ignore', 'inherit', 'inherit']
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* `serviceName` string (optional) - Name of the process that will appear in `name` property of
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[`child-process-gone` event of `app`](app.md#event-child-process-gone).
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Default is `node.mojom.NodeService`.
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* `allowLoadingUnsignedLibraries` boolean (optional) _macOS_ - With this flag, the utility process will be
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launched via the `Electron Helper (Plugin).app` helper executable on macOS, which can be
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codesigned with `com.apple.security.cs.disable-library-validation` and
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`com.apple.security.cs.allow-unsigned-executable-memory` entitlements. This will allow the utility process
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to load unsigned libraries. Unless you specifically need this capability, it is best to leave this disabled.
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Default is `false`.
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Returns [`UtilityProcess`](utility-process.md#class-utilityprocess)
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## Class: UtilityProcess
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> Instances of the `UtilityProcess` represent the Chromium spawned child process
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> with Node.js integration.
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`UtilityProcess` is an [EventEmitter][event-emitter].
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### Instance Methods
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#### `child.postMessage(message, [transfer])`
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* `message` any
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* `transfer` MessagePortMain[] (optional)
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Send a message to the child process, optionally transferring ownership of
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zero or more [`MessagePortMain`][] objects.
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For example:
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```js
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// Main process
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const { port1, port2 } = new MessageChannelMain()
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const child = utilityProcess.fork(path.join(__dirname, 'test.js'))
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child.postMessage({ message: 'hello' }, [port1])
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// Child process
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process.parentPort.once('message', (e) => {
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const [port] = e.ports
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// ...
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})
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```
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#### `child.kill()`
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Returns `boolean`
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Terminates the process gracefully. On POSIX, it uses SIGTERM
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but will ensure the process is reaped on exit. This function returns
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true if the kill is successful, and false otherwise.
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### Instance Properties
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#### `child.pid`
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A `Integer | undefined` representing the process identifier (PID) of the child process.
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If the child process fails to spawn due to errors, then the value is `undefined`. When
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the child process exits, then the value is `undefined` after the `exit` event is emitted.
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#### `child.stdout`
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A `NodeJS.ReadableStream | null` that represents the child process's stdout.
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If the child was spawned with options.stdio[1] set to anything other than 'pipe', then this will be `null`.
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When the child process exits, then the value is `null` after the `exit` event is emitted.
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```js
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// Main process
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const { port1, port2 } = new MessageChannelMain()
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const child = utilityProcess.fork(path.join(__dirname, 'test.js'))
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child.stdout.on('data', (data) => {
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console.log(`Received chunk ${data}`)
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})
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```
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#### `child.stderr`
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A `NodeJS.ReadableStream | null` that represents the child process's stderr.
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If the child was spawned with options.stdio[2] set to anything other than 'pipe', then this will be `null`.
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When the child process exits, then the value is `null` after the `exit` event is emitted.
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### Instance Events
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#### Event: 'spawn'
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Emitted once the child process has spawned successfully.
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#### Event: 'exit'
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Returns:
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* `code` number - Contains the exit code for
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the process obtained from waitpid on posix, or GetExitCodeProcess on windows.
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Emitted after the child process ends.
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#### Event: 'message'
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Returns:
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* `message` any
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Emitted when the child process sends a message using [`process.parentPort.postMessage()`](process.md#processparentport).
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[`child_process.fork`]: https://nodejs.org/dist/latest-v16.x/docs/api/child_process.html#child_processforkmodulepath-args-options
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[Services API]: https://chromium.googlesource.com/chromium/src/+/main/docs/mojo_and_services.md
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[stdio]: https://nodejs.org/dist/latest/docs/api/child_process.html#optionsstdio
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[event-emitter]: https://nodejs.org/api/events.html#events_class_eventemitter
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[`MessagePortMain`]: message-port-main.md
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