SendPortSyncs are created from ReceivePortSyncs. Any message sent through a SendPortSync is delivered to its respective ReceivePortSync. There might be many SendPortSyncs for the same ReceivePortSync.

SendPortSyncs can be transmitted to other isolates.

abstract class SendPortSync {
 /**
  * Sends a synchronous message to this send port and returns the result.
  */
 callSync(var message);

 /**
  * Tests whether [other] is a [SendPortSync] pointing to the same
  * [ReceivePortSync] as this one.
  */
 bool operator==(var other);

 /**
  * Returns an immutable hash code for this send port that is
  * consistent with the == operator.
  */
 int get hashCode;
}