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Application Migration and Development Guide
Application Development with PAS for OpenEdge : PAS for OpenEdge and Client Interaction : Understanding synchronous and asynchronous requests

Understanding synchronous and asynchronous requests

An ABL client and PAS for OpenEdge instance support the following two types of remote procedure execution for both session-managed and session-free applications:
*Synchronous request — (Default) Where the client blocks and waits for the result of the remote request before continuing execution
*Asynchronous request — Where the client continues execution after initiating the request and processes the result whenever the application server makes it available
The ABL client also supports asynchronous requests to industry SOAP Web services, which work much like session-free asynchronous requests to an application server. For more information on ABL asynchronous requests to a SOAP Web service, see OpenEdge Development: Web Services.
Note: OpenEdge does not provide built-in support for asynchronous requests in Open Clients or for OpenEdge Web services. You can implement your own asynchronous request mechanism in Java Open Clients using threads (see OpenEdge Development: Java Open Clients).
* Process control flow
* Specifying the type of remote request
* Handling asynchronous request results
* Asynchronous request queuing
* Understanding the session-managed queuing model
* Understanding the session-free queuing model
* Asynchronous requests and internal procedures
* Tuning the size of the send and response queues