Optimistic concurrency for Mongo DB batch updates

Could anyone suggest me a Java or C# code example? Let’s say I have a Job object:

class Job
{
     public Guid _id { get; set; }
     public Guid _timestamp { get; set; }
     public string title { get; set; }
}

I would like to implement repository which does a batch upsert using optimistic concurrency:

interface IJobRepository {
    Job[] Write(Job[]: jobs)  // returns all it could write  
                              // having updated timestamps 
}