The advantage of using SAVELIST with SAVE is improved performance, especially for applications that manipulate graphic images. The SAVELIST service allows the application to inspect and verify data only in pages that have been changed. In a user list provided by the application, SAVELIST returns the addresses of the first and last page in each range of changed pages within the window. The mapped ranges may be either address spaces, data spaces or hiperspaces. If more than one data space or hiperspace is mapped onto a DIV object, the selected range must be contained within a single data space or hiperspace.
The application must set up a user list before issuing SAVELIST. Upon return from SAVELIST, the first word of each list entry holds the virtual storage address of the first page in a range of changed pages. The second word of the entry holds the virtual storage address of the last changed page in that range. In the last valid entry of the user list, the high-order bit of the first word is set to one.
If the reason code indicates that there are more changed pages that can fit in this list, the first word of the last entry in the list contains an offset (in block number format) into the DIV object from which more changed pages might exist. The second word of the last entry contains the span from the new offset to the block pointed to by the original OFFSET/SPAN combination. If more changed pages can fit in the user list, you can issue SAVE with the current list, and then issue SAVELIST and SAVE again to obtain the additional changed pages and to save them.
ID: Use ID to specify the storage location containing the unique eight-byte name that was returned by IDENTIFY, which connects a particular user with a particular object.
LISTADDR: The LISTADDR parameter specifies the address of the first entry in the user list.
LISTSIZE: The LISTSIZE parameter specifies the number of entries in the list. The size of the list must be a minimum of three entries and a maximum of 255 entries. The SAVELIST service can place addresses in all but the last two entries, which the macro uses as a work area.