Why is this an issue?
Making blocking calls to async methods transforms code that was intended to be asynchronous into a blocking operation. Doing so inside
an Azure Function can lead to thread exhaustion.
| To Do This … |
Instead of This … |
Use This |
Retrieve the result of a background task |
Task.Wait, Task.Result or Task.GetAwaiter.GetResult
|
await
|
Wait for any task to complete |
Task.WaitAny
|
await Task.WhenAny
|
Retrieve the results of multiple tasks |
Task.WaitAll
|
await Task.WhenAll
|
Wait a period of time |
Thread.Sleep
|
await Task.Delay
|
Noncompliant code example
public static class AvoidBlockingCalls
{
[FunctionName("Foo")]
public static async Task<IActionResult> Foo([HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req)
{
// This can lead to thread exhaustion
string requestBody = new StreamReader(req.Body).ReadToEndAsync().Result;
// do stuff...
}
}
Compliant solution
public static class AvoidBlockingCalls
{
[FunctionName("Foo")]
public static async Task<IActionResult> Foo([HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req)
{
string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
// do stuff...
}
}
Resources
