Timers in Durable Functions (Azure Functions)

Durable Functions provides durable timers for use in orchestrator functions to implement delays or to set up timeouts on async actions. Durable timers should be used in orchestrator functions instead of Thread.Sleep or Task.Delay.

You create a durable timer by calling the CreateTimer method in DurableOrchestrationContext. The method returns a task that resumes on a specified date and time.

Timer limitations

When you create a timer that expires at 4:30 pm, the underlying Durable Task Framework enqueues a message which becomes visible only at 4:30 pm. When running in the Azure Functions consumption plan, the newly visible timer message will ensure that the function app gets activated on an appropriate VM.

Warning

Usage for delay

The following example illustrates how to use durable timers for delaying execution. The example is issuing a billing notification every day for ten days.

[FunctionName("BillingIssuer")]
public static async Task Run(
    [OrchestrationTrigger] DurableOrchestrationContext context)
{
    for (int i = 0; i < 10; i++)
    {
        DateTime deadline = context.CurrentUtcDateTime.Add(TimeSpan.FromDays(1));
        await context.CreateTimer(deadline, CancellationToken.None);
        await context.CallFunctionAsync("SendBillingEvent");
    }
}

Warning

Avoid infinite loops in orchestrator functions. For information about how to safely and efficiently implement infinite loop scenarios, see Eternal Orchestrations.

Usage for timeout

This example illustrates how to use durable timers to implement timeouts.

[FunctionName("TryGetQuote")]
public static async Task<bool> Run(
    [OrchestrationTrigger] DurableOrchestrationContext context)
{
    TimeSpan timeout = TimeSpan.FromSeconds(30);
    DateTime deadline = context.CurrentUtcDateTime.Add(timeout);

    using (var cts = new CancellationTokenSource())
    {
        Task activityTask = context.CallFunctionAsync("GetQuote");
        Task timeoutTask = context.CreateTimer(deadline, cts.Token);

        Task winner = await Task.WhenAny(activityTask, timeoutTask);
        if (winner == activityTask)
        {
            // success case
            cts.Cancel();
            return true;
        }
        else
        {
            // timeout case
            return false;
        }
    }
}

Warning

Use a CancellationTokenSource to cancel a durable timer if your code will not wait for it to complete. The Durable Task Framework will not change an orchestration's status to "completed" until all outstanding tasks are completed or cancelled.

This mechanism does not actually terminate in-progress activity function execution. Rather, it simply allows the orchestrator function to ignore the result and move on. If your function app uses the Consumption plan, you will still be billed for any time and memory consumed by the abandoned activity function. By default, functions running in the Consumption plan have a timeout of five minutes. If this limit is exceeded, the Azure Functions host is recycled to stop all execution and prevent a runaway billing situation. The function timeout is configurable.

For a more in-depth example of how to implement timeouts in orchestrator functions, see the Human Interaction & Timeouts - Phone Verification walkthrough.

Next steps