CRM 2015 or 2016 Retrieve Plugin code

public void Execute(IServiceProvider serviceProvider)
{
    // Obtain the execution context from the service provider.
    Microsoft.Xrm.Sdk.IPluginExecutionContext context = (Microsoft.Xrm.Sdk.IPluginExecutionContext)
        serviceProvider.GetService(typeof(Microsoft.Xrm.Sdk.IPluginExecutionContext));

    if (context.Depth == 1)
    {
        IOrganizationServiceFactory serviceFactory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
        IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);

        // Obtain the target entity from the input parmameters.
        EntityReference entity = (EntityReference)context.InputParameters["Target"];

        ColumnSet cols = new ColumnSet(
                             new String[] { "lastname", "firstname", "address1_name" });

        var contact = service.Retrieve("contact", entity.Id, cols);

        if (contact != null)
        {
            if (contact.Attributes.Contains("address1_name") == false)
            {
                contact.Attributes.Add("address1_name", "a default first time value: " );
            }
            else
            {
                contact["address1_name"] = "a value already exist";
            }
            service.Update(contact);
        }
    }
}

message : retrieve

mode : synchronous 

pipeline stage :post operation