How to organize ASP.NET request locking or row locking in DB

I've asp.net page/handler to access images. When performed fist request to the image I resize image to standard size(save on disk) and return it. So I need lock all request to the image except one. This one will resize image. Image identified by 开发者_如何学编程ID in URL, so I guess one lock object required per one image(ID in URL). My question is How can I organize this lock model?

My idea add lock object in Application (Application is synchronized) like this Application.Add(Request[Id], new object()); and use it to locking competitive threads.

This task like row locking of DB or locking element in collection.

Thanks for your replay.

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The easiest way is locking image file with.

using (FileStream fs = new FileStream("image.file", FileMode.Create, FileAccess.Write, FileShare.None))
{

resize image here 

}

When second(third etc) thread try to create file the Exception "The process cannot access the file ..." will throw. And I process this exception in code.