![]() At each await statement, the method immediately exits. ![]() The following examples write text to a file. ![]() Asynchronous calls are faster in UI apps even if a thread pool thread is blocked, because the UI thread isn't blocked during the wait. However, you can use this option if you provide them a Stream that the FileStream class opened. You can't use this option with StreamReader and StreamWriter if you open them directly by specifying a file path. To enable this option, you specify the useAsync=true or options=FileOptions.Asynchronous argument in the constructor call. By using this option, you can avoid blocking a thread pool thread in many cases. For finite control over the file I/O operations, use the FileStream class, which has an option that causes asynchronous I/O to occur at the operating system level. The simple examples in this topic demonstrate File.WriteAllTextAsync and File.ReadAllTextAsync. Asynchronous tasks can easily be run in parallel.The added overhead of using the Async feature is small.For example, a file may be moved to a server that's across the world. The latency of a file access operation might be very low under current conditions, but the latency may greatly increase in the future.They use the existing I/O completion thread briefly at the end. Asynchronous operations often don't need to use a thread during the wait. If the application uses a dedicated thread per response and a thousand requests are being handled simultaneously, a thousand threads are needed. Asynchrony improves the scalability of ASP.NET and other server-based applications by reducing the need for threads.If the UI thread must execute code that takes a long time (for example, more than 50 milliseconds), the UI may freeze until the I/O is complete and the UI thread can again process keyboard and mouse input and other events. Asynchrony makes UI applications more responsive because the UI thread that launches the operation can perform other work.
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