Start tasks only inside a scope that waits for them

How to do it

A task started and forgotten keeps running after its request ends, holds connections, and loses its error. This is called structured concurrency. Use Python's asyncio.TaskGroup from Python 3.11, errgroup in Go, coroutineScope in Kotlin, or task groups in Swift. In JavaScript, Promise.all waits but does not cancel the others, so pass them one shared AbortSignal. Work that must outlive the request goes to a queue, as Move slow work out of the request says. This extends Await every async call.

Examples

Python example

async def load_dashboard(account_id: str) -> Dashboard:
    async with asyncio.TaskGroup() as group:
        invoices = group.create_task(fetch_invoices(account_id))
        usage = group.create_task(fetch_usage(account_id))
        alerts = group.create_task(fetch_alerts(account_id))
    return Dashboard(invoices.result(), usage.result(), alerts.result())

Go example

func loadDashboard(ctx context.Context, accountID string) (Dashboard, error) {
	group, ctx := errgroup.WithContext(ctx)
	var d Dashboard
	group.Go(func() (err error) { d.Invoices, err = fetchInvoices(ctx, accountID); return })
	group.Go(func() (err error) { d.Usage, err = fetchUsage(ctx, accountID); return })
	group.Go(func() (err error) { d.Alerts, err = fetchAlerts(ctx, accountID); return })
	return d, group.Wait()
}

How to check

A lint or search rule finds no asyncio.create_task outside a task group and no bare go statement in request handlers. A test makes one of three tasks fail and asserts that the other two were cancelled.

Sources

• Python asyncio, Task groups

Related rules

• SCL-16 Move slow work out of the request in Scaling
• ARC-33 Await every async call in Clean code and architecture