We have a long running user operation that is handled by a pool of worker processes. Data input and output is from Azure SQL.

The master Azure SQL table structure columns are approximated to

[UserId, col1, col2, ... , col N, beingProcessed, lastTimeProcessed ] 

beingProcessed is boolean and lastTimeProcessed is DateTime. The logic in every worker role is:

public void WorkerRoleMain()
{
    while(true)
    {
        try
        {
            dbContext db = new dbContext();

            // Read
            foreach (UserProfile user in db.UserProfile
                    .Where(u => DateTime.UtcNow.Subtract(u.lastTimeProcessed) 
                            > TimeSpan.FromHours(24) & 
                            u.beingProcessed == false))
            {
                user.beingProcessed = true; // Modify
                db.SaveChanges();           // Write
                // Do some long drawn processing here
                ...
                ...
                ...
                user.lastTimeProcessed = DateTime.UtcNow;
                user.beingProcessed = false;
                db.SaveChanges();
            }
        }
        catch(Exception ex)
        {
            LogException(ex);
            Sleep(TimeSpan.FromMinutes(5));
        }
    } // while ()
}

With multiple workers processing as above (each with their own Entity Framework layer), in essence beingProcessed is being used a lock for MutEx purposes

Question: How can I deal with concurrency issues on the beingProcessed "lock" itself based on the above load? I think read-modify-write operation on the beingProcessed needs to be atomic but I'm open to other strategies. Open to other code refinements too.