Function signal

Sends a signal payload to a paused workflow thread that is awaiting this signalId via waitFor(). Signals are the primary mechanism for inter-workflow communication and for delivering results from hook functions back to the orchestrating workflow.

signal is the send side of the coordination pair. The receive side is waitFor(). A signal can be sent from:

• Another workflow function
• A hook function (most common pattern with execHook)
• An external client via Durable.Client.workflow.signal()

Signals fire exactly once per workflow execution — the isSideEffectAllowed guard ensures they are not re-sent on replay.

Examples

import { Durable } from '@hotmeshio/hotmesh';

// Hook function that signals completion back to the parent workflow
export async function processOrder(
  orderId: string,
  signalInfo?: { signal: string; $durable: boolean },
): Promise<{ total: number }> {
  const { calculateTotal } = Durable.workflow.proxyActivities<typeof activities>();
  const total = await calculateTotal(orderId);

  // Signal the waiting workflow with the result
  if (signalInfo?.signal) {
    await Durable.workflow.signal(signalInfo.signal, { total });
  }
  return { total };
}
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// Cross-workflow coordination: workflow A signals workflow B
export async function coordinatorWorkflow(): Promise<void> {
  const { prepareData } = Durable.workflow.proxyActivities<typeof activities>();
  const data = await prepareData();

  // Signal another workflow that is paused on waitFor('data-ready')
  await Durable.workflow.signal('data-ready', { payload: data });
}
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// External signal from an API handler (outside a workflow)
const client = new Durable.Client({ connection });
await client.workflow.signal('approval-signal', { approved: true });
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