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Exception Description Look Ahead Facility

IP.com Disclosure Number: IPCOM000052758D
Original Publication Date: 1981-Jul-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 48K

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Bains, RL: AUTHOR [+3]


This facility allows the Programming System (PS) to provide additional exception-handling services over and above those provided by the machine product as follows:

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Exception Description Look Ahead Facility

This facility allows the Programming System (PS) to provide additional exception-handling services over and above those provided by the machine product as follows:

1. Defining additional search criteria beyond that provided by the machine. For example, exceptions can be qualified by the type of communication they are being signaled in support of. (The term ""type of exception'' is used in this sense in all instances.)

2. Determining if an exception being signaled to a program will be handled by that program. This allows the PS to take default action appropriate to the type of exception.

3. Determining how an exception will be handled by the program to which it is signaled. This allows the PS to prevent invalid handling actions for particular types of exceptions. For example, if a particular type of exception requires control to return to the signaler, the PS can prevent handling actions that terminate the signaler.

4. Providing additional exception-handling services to the monitoring program. For example, the monitoring program can request that a dump be taken and the exception be logged.

5. Preventing invalid exception-handling sequences. For example, recursive invocations of the same exception handler for the same execution can be prevented.

An exception description is a program data object that allows a program to monitor for exceptional conditions signaled to it by either the machine or a called program. The exception description specifies the exceptions to be monitored, by exception identifier and compare value, and how these exceptions are to be handled. A program invocation can contain one or more exception descriptions that are searched sequentially when an exception is signaled. If the Signal Exception instruction locates a matching exception description, the handling action specified is taken.

If no matching exception description is found, the program defined by the operating system as the Process Default Exception Handler (PDEH) is invoked to take system action. Machine-signaled exceptions can be trapped by the PDEH by establishing a PS convention that prevents direct handling of these exceptions. This allows the PS to use the look-ahead facility described herein to provide additional services in handling machine-signaled exceptions. PS- provided programs for signaling program-defined exceptions can use the look- ahead facility directly to provide additional services.

The Exception Description (EXCD) program object is modified to include a program re...