The following chart describes the installation flow of ENQ/DEQ exits.

Figure 1. ENQ/DEQ exits installation flow

System programmers only use RNLs and either the ISGNQXITFAST or ISGNQXIT installation exit. All of the other exits are intended for the independent software vendors (ISVs).

As of V1R9 and later, the installation exits that are used by the ISVs and the ISGNQXITFAST exit (not the ISGNQXIT exit) can get control in a cross memory environment.

See "Global Resource Serialization Exits" topic in z/OS MVS Installation Exits for more information about the GRS exits.