Avoid blocking calls in .NET Core and C# applications. Blocking calls are synchronous calls that block the execution of the current thread until the operation is completed. This can lead to performance issues, especially in applications that handle a large number of requests or have long-running operations. Instead, use asynchronous calls that allow the thread to continue executing while the operation is in progress.

Asynchronous calls in .NET Core and C# are implemented using the async and await keywords. The async keyword is used to mark a method as asynchronous, and the await keyword is used to wait for the completion of an asynchronous operation. When an asynchronous method is called, it returns a Task or Task object that represents the ongoing operation. The calling thread can continue executing other tasks while the operation is in progress. When the operation is completed, the result is returned to the calling thread.

Here's an example of a blocking call that reads a file synchronously:

varcontents = File.ReadAllText("file.txt");

And here's an example of an asynchronous call that reads a file asynchronously:

varcontents = await File.ReadAllTextAsync("file.txt");

By using asynchronous calls instead of blocking calls, you can improve the performance and scalability of your .NET Core and C# applications.