Similar to a session-free AppServer request, the order of completion for an asynchronous Web service request is determined solely by the Web service. The manner in which the ABL client send and response queues for an asynchronous request handle messages is identical for both session-free asynchronous AppServer requests and asynchronous Web service requests. That is, if ABL invokes multiple asynchronous Web service requests, the order of their completion cannot be determined on the Web service or session-free AppServer client. So, you must write your mainline program, and indeed your asynchronous event procedures, to make no assumptions about the order in which multiple asynchronous Web service requests complete.

A subtle distinction between a session-free asynchronous AppServer request and an asynchronous Web service request is the SOAP response callback procedure available for the Web service request. If a SOAP response callback procedure is set for an asynchronous Web service request, it executes after the SOAP response message arrives at the client but before the asynchronous event procedure executes to handle the PROCEDURE-COMPLETE event for the request.