abort-signal-timeout-in-workflow

Error

AbortSignal.timeout() is not supported in workflow functions.
Use sleep() with an AbortController instead.

Why This Happens

AbortSignal.timeout() creates a signal that aborts after a real-time delay using an internal timer. Workflow functions must be deterministic to support replay — they run the same code multiple times during the workflow's lifecycle, using the event log to resume execution to the correct point.

Real-time timers break this determinism because:

• On the first execution, the timer might fire after 10 seconds
• On replay, the timer would fire again, but the event log may have already advanced past that point
• The timer's behavior depends on wall-clock time, which varies between executions

How to Fix

Use sleep() with an AbortController to create a deterministic timeout that cancels in-flight work:

Before (incorrect):

export async function workflow() {
  "use workflow";

  // This will throw an error
  const signal = AbortSignal.timeout(10_000); 
  const result = await fetchData(signal);
  return result;
}

After (correct):

import { sleep } from "workflow";

export async function workflow() {
  "use workflow";

  const controller = new AbortController(); 
  void sleep("10s").then(() => controller.abort()); 

  return await fetchData(controller.signal);
}

async function fetchData(signal: AbortSignal) {
  "use step";
  const response = await fetch("https://api.example.com/data", { signal });
  return response.json();
}

The sleep() + AbortController pattern is the durable equivalent of AbortSignal.timeout(). The sleep is recorded in the event log, so it replays deterministically. If fetchData finishes within 10 seconds you get the response; if not, the timer fires controller.abort(), fetch rejects with an AbortError, and the step's failure propagates to the workflow as a FatalError (no retries — abort is intentional cancellation).

Related

• Cancellation — Patterns for cancelling in-flight work
• sleep() API Reference — Durable sleep primitive
• Workflows and Steps — Why workflow functions must be deterministic
• setTimeout in Workflow — Similar restriction on setTimeout