public class Example
{
    public void Thread1()
    {
        Contract.ContractFailed += Thread1Failed;
        // Do thread 1 things
        Contract.ContractFailed -= Thread1Failed;
    }

    private static void Thread1Failed(object sender, ContractFailedEventArgs e)
    {
        Console.Error.WriteLine("Thread 1: " + e.Message);
        e.SetHandled();
    }

    public void Thread2()
    {
        Contract.ContractFailed += Thread2Failed;
        // Do thread 2 things
        Contract.ContractFailed -= Thread2Failed;
    }

    private static void Thread2Failed(object sender, ContractFailedEventArgs e)
    {
        Console.Error.WriteLine("Thread 2: " + e.Message);
        e.SetHandled();
    }
}