ALET reuse by the system

ALETs are not unique; they index a specific entry on a PASN-AL or DU-AL, connecting a program to an address/data space. When ALESERV DELETE removes an access list entry, the connection between the ALET and the space no longer exists. The access list entry and its corresponding ALET are available for the system to use again. The breaking of the connection and the reuse of the ALET mean that a program using the old ALET:

Does not gain access to the space
Might gain access to another space

The system does not check and notify programs about the reuse of an ALET. Therefore, when a program uses ALESERV DELETE to delete an access list entry, the program must ensure that other programs do not use the old ALET.

Consider a program, PROGA, deleting the data space, DSA, and removing the entry from the PASN-AL. The ALET for that entry, ALETA, ceases to have meaning in relationship to DSA. The system, free now to reuse that ALET, assigns ALETA to a new data space, DSB. Suppose other programs in the address space were also using ALETA to access DSA. If PROGA does not tell those programs about the removal of ALETA, those programs will mistakenly access DSB, while intending to access DSA.

This response to the system's removal of the entry and reuse of an ALET is similar to the work a program does after it frees address space storage that it obtained and shared with other programs. When that area of storage is freed, MVS™ reuses the area to satisfy a later request for storage. When an access list entry is freed, MVS reuses that ALET to satisfy a later ALESERV ADD request.