gradio

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// A hack to load a worker script from a different origin.
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// Vite's built-in Web Workers feature does not support inlining the worker code
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// into the main bundle and always emits it to a separate file,
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// which is not compatible with the cross-origin worker.
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// So we use this hack to load the separate worker code from a domain different from the parent page.
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// Vite deals with the special syntax `new Worker(new URL("worker.ts", import.meta.url))` for the worker build,
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// so this `CrossOriginWorkerMaker` class must be defined in a separate file and
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// be imported as the `Worker` alias into the file where the syntax is used to load the worker.
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// This implementation was based on https://github.com/whitphx/stlite/blob/v0.34.0/packages/kernel/src/kernel.ts,
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// and this technique was introduced originally for Webpack at https://github.com/webpack/webpack/discussions/14648#discussioncomment-1589272
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// Caching is important not only for performance but also for ensuring that the same blob URL is used for the same requested URL.
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const worker_blob_url_cache = new Map<string, string>();
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function get_blob_url(url: URL): string {
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	const cached_worker_blob_url = worker_blob_url_cache.get(url.toString());
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	if (cached_worker_blob_url) {
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		console.debug(`Reusing the cached worker blob URL for ${url.toString()}.`);
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		return cached_worker_blob_url;
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	}
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	const worker_blob = new Blob([`importScripts("${url.toString()}");`], {
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		type: "text/javascript"
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	});
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	const worker_blob_url = URL.createObjectURL(worker_blob);
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	worker_blob_url_cache.set(url.toString(), worker_blob_url);
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	return worker_blob_url;
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}
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export class CrossOriginWorkerMaker {
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	public readonly worker: Worker | SharedWorker;
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	constructor(url: URL, options?: WorkerOptions & { shared?: boolean }) {
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		const { shared = false, ...workerOptions } = options ?? {};
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		try {
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			// This is the normal way to load a worker script, which is the best straightforward if possible.
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			this.worker = shared
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				? new SharedWorker(url, workerOptions)
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				: new Worker(url, workerOptions);
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		} catch (e) {
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			console.debug(
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				`Failed to load a worker script from ${url.toString()}. Trying to load a cross-origin worker...`
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			);
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			const worker_blob_url = get_blob_url(url);
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			this.worker = shared
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				? new SharedWorker(worker_blob_url, workerOptions)
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				: new Worker(worker_blob_url, workerOptions);
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		}
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	}
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}
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