Concurrency in asp.net

Hi everybody,

I need to understand how concurrency excatlywork in asp.net. For example, I'm confused what happens if two users atthe same time try to access the same record in a table or even the samevariable. Do ASP.NET handle this , I mean by locking one user andletting the other to have access OR it's up to the programmer to writesome code to lock shared resources such as database , objects andvariables?

If it's up to the programmer to do this task, I appreciate if you can show me an example that clarifies that.

Thank you

ADO.NET uses a disconnected data model, meaning that in theory, nothings knows 2 users are accessing the same record at the same time. When you read a record, and the record is displayed, there is no connection left on the database. Therefore there is no "concurrency", so to speak, because for all general purpose, the users only see the record's -content-, not the record itself. This is required because the web is a stateless environment...you cannot keep a live connection to the server.

Thus, the only really effective way of handling this (there are other ways, but this is the all purpose one), is called Optimistic Concurrency. The record is read, and when you attempt to update it, ADO.NET (only IF you ask it to do so), will check if the record changed (by storing the original values) since it was read by the user. If it did, it will complain and tell you that someone else changed the record between the last time you read it and your update. Otherwise, it will write it normally.

If 2 people attempt to write the record at the exact same time ( I mean, there are 2 open connections on the same record at the exact same instant), then it is up to the DBMS to handle this, ADO.NET has no control over it. Usualy what will happen is one of the users will be given the go (first come first serve), and the second update will trigger the Optimistic Concurrency mechanism I just talked about.

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This article tell you how to Handling Concurrency Issues in .NET