Parallelism Plugin Dynamics crm

Hi all , I have a plugin and For better performance they ask me to do Parallelism ,Could any one help me with syntax programming ?

var listOfContactsToUpdate = (from contact in spCtx.ContactSet
select contact).ToList();

foreach (Contact contact in listOfContactsToUpdate)
{  

// Update email Pressure
contact.oab_pressionrelationnellejourEmail = 0;
contact.oab_PressionRelationnelleSemaineEmail =emaildal.GetPressionCommercialSemaineparContact(contact, orgService);
  Contact contactToUpdate = new Contact()

{
Id = contact.Id,
oab_pressionrelationnellejourEmail = contact.oab_pressionrelationnellejourEmail,
oab_PressionRelationnelleJourAppelTlphonique = contact.oab_PressionRelationnelleJourAppelTlphonique,
 };
UpdateRequest updateRequest = new UpdateRequest { Target = contactToUpdate };
requestWithResults.Requests.Add(updateRequest);
}