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122 lines
2.8 KiB
Markdown
122 lines
2.8 KiB
Markdown
## Workers
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Deno supports
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[`Web Worker API`](https://developer.mozilla.org/en-US/docs/Web/API/Worker/Worker).
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Workers can be used to run code on multiple threads. Each instance of `Worker`
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is run on a separate thread, dedicated only to that worker.
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Currently Deno supports only `module` type workers; thus it's essential to pass
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the `type: "module"` option when creating a new worker.
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Relative module specifiers are
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[not supported](https://github.com/denoland/deno/issues/5216) at the moment. You
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can instead use the `URL` contructor and `import.meta.url` to easily create a
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specifier for some nearby script.
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```ts
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// Good
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new Worker(new URL("worker.js", import.meta.url).href, { type: "module" });
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// Bad
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new Worker(new URL("worker.js", import.meta.url).href);
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new Worker(new URL("worker.js", import.meta.url).href, { type: "classic" });
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new Worker("./worker.js", { type: "module" });
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```
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### Permissions
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Creating a new `Worker` instance is similar to a dynamic import; therefore Deno
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requires appropriate permission for this action.
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For workers using local modules; `--allow-read` permission is required:
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**main.ts**
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```ts
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new Worker(new URL("worker.ts", import.meta.url).href, { type: "module" });
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```
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**worker.ts**
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```ts
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console.log("hello world");
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self.close();
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```
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```shell
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$ deno run main.ts
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error: Uncaught PermissionDenied: read access to "./worker.ts", run again with the --allow-read flag
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$ deno run --allow-read main.ts
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hello world
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```
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For workers using remote modules; `--allow-net` permission is required:
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**main.ts**
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```ts
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new Worker("https://example.com/worker.ts", { type: "module" });
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```
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**worker.ts** (at https[]()://example.com/worker.ts)
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```ts
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console.log("hello world");
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self.close();
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```
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```shell
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$ deno run main.ts
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error: Uncaught PermissionDenied: net access to "https://example.com/worker.ts", run again with the --allow-net flag
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$ deno run --allow-net main.ts
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hello world
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```
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### Using Deno in worker
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> This is an unstable Deno feature. Learn more about
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> [unstable features](./stability.md).
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By default the `Deno` namespace is not available in worker scope.
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To add the `Deno` namespace pass `deno: true` option when creating new worker:
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**main.js**
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```ts
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const worker = new Worker(new URL("worker.js", import.meta.url).href, {
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type: "module",
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deno: true,
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});
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worker.postMessage({ filename: "./log.txt" });
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```
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**worker.js**
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```ts
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self.onmessage = async (e) => {
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const { filename } = e.data;
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const text = await Deno.readTextFile(filename);
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console.log(text);
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self.close();
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};
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```
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**log.txt**
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```
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hello world
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```
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```shell
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$ deno run --allow-read --unstable main.js
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hello world
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```
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When the `Deno` namespace is available in worker scope, the worker inherits its
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parent process' permissions (the ones specified using `--allow-*` flags).
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We intend to make permissions configurable for workers.
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