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* docs: update functions background tasks guide * Update apps/docs/content/guides/functions/background-tasks.mdx Co-authored-by: Chris Chinchilla <chris.ward@supabase.io> --------- Co-authored-by: Chris Chinchilla <chris.ward@supabase.io>
89 lines
2.9 KiB
Plaintext
89 lines
2.9 KiB
Plaintext
---
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id: 'function-background-tasks'
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title: 'Background Tasks'
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description: 'How to run background tasks in an Edge Function outside of the request handler'
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subtitle: 'Run background tasks in an Edge Function outside of the request handler.'
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---
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Edge Function instances can process background tasks outside of the request handler. Background tasks are useful for asynchronous operations like uploading a file to Storage, updating a database, or sending events to a logging service. You can respond to the request immediately and leave the task running in the background.
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This allows you to:
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- Respond quickly to users while processing continues
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- Handle async operations without blocking the response
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---
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## Overview
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You can use `EdgeRuntime.waitUntil(promise)` to explicitly mark background tasks. The Function instance continues to run until the promise provided to `waitUntil` completes.
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```ts
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// Mark the asyncLongRunningTask's returned promise as a background task.
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// ⚠️ We are NOT using `await` because we don't want it to block!
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EdgeRuntime.waitUntil(asyncLongRunningTask())
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Deno.serve(async (req) => {
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return new Response(...)
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})
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```
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You can call `EdgeRuntime.waitUntil` in the request handler too. This will not block the request.
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```ts
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Deno.serve(async (req) => {
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// Won't block the request, runs in background.
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EdgeRuntime.waitUntil(asyncLongRunningTask())
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return new Response(...)
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})
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```
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You can listen to the `beforeunload` event handler to be notified when the Function is about to be shut down.
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```tsx
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EdgeRuntime.waitUntil(asyncLongRunningTask())
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// Use beforeunload event handler to be notified when function is about to shutdown
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addEventListener('beforeunload', (ev) => {
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console.log('Function will be shutdown due to', ev.detail?.reason)
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// Save state or log the current progress
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})
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Deno.serve(async (req) => {
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return new Response(...)
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})
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```
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## Handling errors
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We recommend using `try`/`catch` blocks within your background task function to handle errors.
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You can also add an event listener to [`unhandledrejection`](https://developer.mozilla.org/en-US/docs/Web/API/Window/unhandledrejection_event) to handle any promises without a rejection handler.
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```tsx
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addEventListener('unhandledrejection', (ev) => {
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console.log('unhandledrejection', ev.reason)
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ev.preventDefault()
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})
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```
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<Admonition type="note">
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The maximum duration is capped based on the wall-clock, CPU, and memory limits. The function will shut down when it reaches one of these [limits](/docs/guides/functions/limits).
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</Admonition>
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---
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## Testing background tasks locally
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When testing Edge Functions locally with Supabase CLI, the instances are terminated automatically after a request is completed. This will prevent background tasks from running to completion.
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To prevent that, you can update the `supabase/config.toml` with the following settings:
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```toml
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[edge_runtime]
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policy = "per_worker"
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```
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