I'm trying to understand how and when to use async
programming and got to I/O bound operations, but I don't understand them. I want to implement them from scratch. How can I do that?
Consider the example below which is synchronous:
private void DownloadBigImage() {
var url = "https://cosmos-magazine.imgix.net/file/spina/photo/14402/180322-Steve-Full.jpg";
new WebClient().DownloadFile(url, "image.jpg");
}
How do I implement the async
version by only having the normal synchronous method DownloadBigImage
without using Task.Run
since that will use a thread from the thread pool only for waiting - that's just being wasteful!
Also do not use the special method that's already async
! This is the purpose of this question: how do I make it myself without relying on methods which are already async? So, NO things like:
await new WebClient().DownloadFileTaskAsync(url, "image.jpg");
Examples and documentation available are very lacking in this regard. I found only this: https://learn.microsoft.com/en-us/dotnet/standard/async-in-depth which says:
The call to GetStringAsync() calls through lower-level .NET libraries (perhaps calling other async methods) until it reaches a P/Invoke interop call into a native networking library. The native library may subsequently call into a System API call (such as write() to a socket on Linux). A task object will be created at the native/managed boundary, possibly using TaskCompletionSource. The task object will be passed up through the layers, possibly operated on or directly returned, eventually returned to the initial caller.
Basically I have to use a "P/Invoke interop call into a native networking library"... but how?