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Exception Handling Overview
Optionally recovering from the exception by passing the exception information
to a piece of code to take any necessary actions.
When a run-time error occurs, an exception message is generated. An exception
message has one of the following types depending on the error which occurred:
*ESCAPE
Indicates that a severe error has been detected.
*STATUS Describes the status of work being done by a program.
*NOTIFY Describes a condition requiring corrective action or reply from the calling
program.
Function Check
Indicates that one of the three previous exceptions occurred and was
not handled.
Exception messages are associated with call stack entries. Each call stack entry is
in turn associated with a list of exception handlers defined for that entry. (See “The
Call Stack” on page 129 for further discussion of a call stack.)
Figure 108 on page 219 shows a call stack where an OPM program calls an
ILEprogram consisting of several modules and therefore several procedures. Refer
to this figure in the discussions which follow.
In general, when an exception occurs, the handlers associated with the call stack
entry are given a chance to handle the exception. If the exception is not handled by
any of the handlers on the list then it is considered to be unhandled, at which point
the following default actions are taken for the unhandled exception:
1. If the exception is a function check, the call stack entry is removed from the
stack.
2. The exception is moved (percolated) to the previous call stack entry.
3. The exception handling process is restarted for this call stack entry.
The action of allowing the previous call stack entry to handle an exception is
referred to as percolation. Percolation continues until the exception is handled, or
until the control boundary is reached. A control boundary is a call stack entry for
which the immediately preceding call stack entry is in a different activation group or
is an OPM program. In Figure 108 on page 219 Procedure P1 is the control
boundary.
218 ILE RPG for AS/400 Programmer's Guide