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 "sleep" or "delay" APIs that may be built into the language.

Durable timers are tasks that are created using the appropriate "create timer" API for the provided language, as shown below, and take either a due time or a duration as an argument.

// Put the orchestrator to sleep for 72 hours
DateTime dueTime = context.CurrentUtcDateTime.AddHours(72);
await context.CreateTimer(dueTime, CancellationToken.None);

When you "await" the timer task, the orchestrator function will sleep until the specified expiration time.

Note

Orchestrations will continue to process other incoming events while waiting for a timer task to expire.

Timer limitations

When you create a timer that expires at 4:30 pm UTC, the underlying Durable Task Framework enqueues a message that becomes visible only at 4:30 pm UTC. If the function app is scaled down to zero instances in the meantime, the newly visible timer message will ensure that the function app gets activated again on an appropriate VM.

Note

  • Starting with version 2.3.0 of the Durable Extension, Durable timers are unlimited for .NET apps. For JavaScript, Python, and PowerShell apps, as well as .NET apps using earlier versions of the extension, Durable timers are limited to six days. When you are using an older extension version or a non-.NET language runtime and need a delay longer than six days, use the timer APIs in a while loop to simulate a longer delay.
  • Don't use built-in date/time APIs for getting the current time. When calculating a future date for a timer to expire, always use the orchestrator function's current time API. For more information, see the orchestrator function code constraints article.

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 10 days.

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

Note

The previous C# example targets Durable Functions 2.x. For Durable Functions 1.x, you must use DurableOrchestrationContext instead of IDurableOrchestrationContext. For more information about the differences between versions, see the Durable Functions versions article.

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] IDurableOrchestrationContext context)
{
    TimeSpan timeout = TimeSpan.FromSeconds(30);
    DateTime deadline = context.CurrentUtcDateTime.Add(timeout);

    using (var cts = new CancellationTokenSource())
    {
        Task activityTask = context.CallActivityAsync("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;
        }
    }
}

Note

The previous C# example targets Durable Functions 2.x. For Durable Functions 1.x, you must use DurableOrchestrationContext instead of IDurableOrchestrationContext. For more information about the differences between versions, see the Durable Functions versions article.

Warning

In .NET, JavaScript, Python, and PowerShell, you must cancel any created durable timers if your code will not wait for them to complete. See the examples above for how to cancel pending timers. The Durable Task Framework will not change an orchestration's status to "Completed" until all outstanding tasks, including durable timer tasks, are either completed or canceled.

This cancellation mechanism using the when-any pattern doesn't terminate in-progress activity function or sub-orchestration executions. Rather, it simply allows the orchestrator function to ignore the result and move on. If your function app uses the Consumption plan, you'll 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 article.

Next steps