Release 10.1A: OpenEdge Application Server:
Developing AppServer Applications

Executing an asynchronous request

You execute an asynchronous request using the RUN statement with the ASYNCHRONOUS option (the RUN...ASYNCHRONOUS statement). With this option, you can specify a variable to return an asynchronous request handle used to uniquely identify and maintain the status of the asynchronous request. You can also specify an internal procedure to use as the event procedure to handle the response from the asynchronous request. For more information on the RUN...ASYNCHRONOUS statement, see the RUN statement entry in OpenEdge Development: Progress 4GL Reference .

When specifying the RUN...ASYNCHRONOUS statement, you can also include INPUT, OUTPUT, and INPUT-OUTPUT parameters similar to the parameters on a synchronous RUN statement. As with the synchronous RUN statement, the input parameters represent values passed to the remote procedure. However, unlike the synchronous RUN statement, the output parameters do not return results from the remote procedure directly on the RUN...ASYNCHRONOUS statement. The values for these output parameters are not available until the asynchronous request completes and the client handles the associated PROCEDURE-COMPLETE event. On detecting this event, the client executes the specified event procedure, which returns the values as input parameters to the event procedure. Thus, the output parameters on the RUN...ASYNCHRONOUS statement serve only as placeholders to map the signature of the remote procedure on the AppServer. For more information, see the "Handling the response from an asynchronous request" section.

Asynchronous request handles

Associated with each asynchronous request is an asynchronous request handle. An instance of this handle is created each time you execute the RUN...ASYNCHRONOUS statement. Thus, you can use this handle to obtain information on a specific asynchronous request.

The Progress 4GL client allows you to access this handle in three ways:

Using the SET async-request-handle option on the RUN...ASYNCHRONOUS statement.
Using the FIRST-ASYNC-REQUEST and LAST-ASYNC-REQUEST attributes of the server handle or the NEXT-SIBLING and PREV-SIBLING attributes of the asynchronous request handle to walk through the valid asynchronous request handles for the specified AppServer.
Accessing the SELF system handle within an event procedure in response to the asynchronous request.

For more information on using the asynchronous request handle, see the "Handling the response from an asynchronous request" section.