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.

[frame=all]
[cols="^1,^1,^1"]
|===
|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++``
|===

// If you want to factorize the description uncomment the following line and create the file.
//include::../description.adoc[]

== Noncompliant Code Example

[source,csharp]
----

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

[source,csharp]
----

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...
	}
}

----

== See

* https://msdn.microsoft.com/en-us/magazine/jj991977.aspx[Async/Await - Best Practices in Asynchronous Programming]
* https://docs.microsoft.com/en-us/azure/azure-functions/performance-reliability#use-async-code-but-avoid-blocking-calls[Improve the performance and reliability of Azure Functions - Scalability best practices]
* S4462 - a more generic rule about detecting blocking calls to ``++async++`` methods.

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== Implementation Specification
(visible only on this page)

The implementation should be common with S4462. When implementing, should make sure S4462 will ignore Azure Functions.
