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Lakshan PereraandCharis
1eebae921c
* chore: add WebSockets guide * update the limits * add missing navigation link * Apply suggestions from code review Co-authored-by: Charis <26616127+charislam@users.noreply.github.com> * formatting --------- Co-authored-by: Charis <26616127+charislam@users.noreply.github.com>
76 lines
2.8 KiB
Plaintext
76 lines
2.8 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: 'How to 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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### How it works
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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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The maximum duration is capped based on the wall-clock, CPU, and memory limits. The Function will shutdown when it reaches one of these [limits](/docs/guides/functions/limits).
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You can listen to the `beforeunload` event handler to be notified when Function invocation is about to be shut down.
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### Example
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Here's an example of using `EdgeRuntime.waitUntil` to run a background task and using `beforeunload` event to be notified when the instance is about to be shut down.
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```ts
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async function longRunningTask() {
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// do work here
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}
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// Mark the longRunningTask's returned promise as a background task.
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// note: we are not using await because we don't want it to block.
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EdgeRuntime.waitUntil(longRunningTask())
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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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// Invoke the function using a HTTP request.
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// This will start the background task
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Deno.serve(async (req) => {
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return new Response('ok')
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})
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```
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### Starting a background task in the request handler
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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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async function fetchAndLog(url: string) {
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const response = await fetch(url)
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console.log(response)
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}
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Deno.serve(async (req) => {
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// this will not block the request,
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// instead it will run in the background
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EdgeRuntime.waitUntil(fetchAndLog('https://httpbin.org/json'))
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return new Response('ok')
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})
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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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When running with `per_worker` policy, Function won't auto-reload on edits. You will need to manually restart it by running `supabase functions serve`.
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