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import { fileURLToPath } from 'node:url';
import { Worker, parentPort } from 'node:worker_threads';
/**
* Runs a task in a subprocess so any dangling stuff gets killed upon completion.
* The subprocess needs to be the file `forked` is called in, and `forked` needs to be called eagerly at the top level.
* @template T
* @template U
* @param {string} module `import.meta.url` of the file
* @param {(opts: T) => Promise<U>} callback The function that is invoked in the subprocess
* @returns {(opts: T) => Promise<U>} A function that when called starts the subprocess
*/
export function forked(module, callback) {
if (process.env.SVELTEKIT_FORK && parentPort) {
parentPort.on(
'message',
/** @param {any} data */ async (data) => {
if (data?.type === 'args' && data.module === module) {
parentPort?.postMessage({
type: 'result',
module,
payload: await callback(data.payload)
});
}
}
);
parentPort.postMessage({ type: 'ready', module });
}
/**
* @param {T} opts
* @returns {Promise<U>}
*/
return function (opts) {
return new Promise((fulfil, reject) => {
const worker = new Worker(fileURLToPath(module), {
env: {
...process.env,
SVELTEKIT_FORK: 'true'
}
});
worker.on(
'message',
/** @param {any} data */ (data) => {
if (data?.type === 'ready' && data.module === module) {
worker.postMessage({
type: 'args',
module,
payload: opts
});
}
if (data?.type === 'result' && data.module === module) {
worker.unref();
fulfil(data.payload);
}
}
);
worker.on('exit', (code) => {
if (code) {
reject(new Error(`Failed with code ${code}`));
}
});
});
};
}
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