Handle Cursors and Resume Cursors

To process exceptions, the system uses two pointers called the handle cursor and resume cursor. These pointers keep track of the progress of exception handling. You need to understand the use of the handle cursor and resume cursor under certain advanced error-handling scenarios. These concepts are used to explain additional error-handling features in later topics.

The handle cursor is a pointer that keeps track of the current exception handler. As the system searches for an available exception handler, it moves the handle cursor to the next handler in the exception handler list defined by each call stack entry. This list can contain:

Direct monitor handlers
ILE condition handlers
HLL-specific handlers

The handle cursor moves down the exception handler list to lower priority handlers until the exception is handled. If the exception is not handled by any of the exception handlers that have been defined for a call stack entry, the handle cursor moves to the first (highest priority) handler for the previous call stack entry.

The resume cursor is a pointer that keeps track of the current location at which your exception handler can resume processing after handling the exception. Normally the system sets the resume cursor to the next instruction following the occurrence of an exception. For call stack entries above the procedure that incurred the exception, the resume point is directly after the procedure or program call that currently suspended the procedure or program. To move the resume cursor to an earlier resume point, use the Move Resume Cursor (CEEMRCR) bindable API.

Figure 1 shows an example of the handle cursor and resume cursor.

Figure 1. Handle Cursor and Resume Cursor Example

Handle Cursor and Resume Cursor Example

The handle cursor is currently at the second exception handler defined in the exception handler priority list for procedure P2. The handler procedure P10 is currently called by the system. If procedure P10 handles the exception and returns, control goes to the current resume cursor location defined in procedure P3. This example assumes that procedure P3 percolated the exception to procedure P2.

The exception handler procedure P10 can modify the resume cursor with the Move Resume Cursor (CEEMRCR) bindable API. Two options are provided with this API. An exception handler can modify the resume cursor to either of the following:

The call stack entry containing the handle cursor
The call stack entry prior to the handle cursor

In Figure 1, you could modify the resume cursor to either procedure P2 or P1. After the resume cursor is modified and the exception is marked as handled, a normal return from your exception handler returns control to the new resume point.