Setting up

The service provider first obtains a system LX. MVS™ sets aside part of the available LXs for use as system LXs. When the service provider connects an entry table to a system LX, the entry table is connected to all present and future address spaces.

Unlike a non-system LX, a non-reusable system LX cannot be freed for reuse. When an address space that owns a non-reusable system LX terminates, the LX becomes dormant. The system allows a dormant system LX to be reconnected to an address space different from the original owning address space. This is an important consideration for a service provider that can be terminated and then restarted. The service provider must have a way to remember the non-reusable system LX it owned so that it can connect the LX to an entry table when it is restarted. A reusable system LX, on the other hand, can be freed for reuse. See Reassigning LXs when the LX reuse facility is enabled for more information.

In the example, the service provider would first test LXVALUE. If LXVALUE was zero, the service provider would issue the LXRES macro. Otherwise the service provider would pass the value found in LXVALUE to the ETCON macro.

The code shown in the following three steps runs with the service provider's address space as the home address space. The first step obtains a system LX. If the service provider's address space is coming up for the first time since IPL, the service provider issues the LXRES macro with the SYSTEM=YES option. The service provider must then save the LX somewhere, probably in common storage, so it is accessible if the service provider is restarted.

         LA     2,1
         ST     2,LXCOUNT     REQUEST 1 SYSTEM LX
GETSLX   LXRES  LXLIST=LXL,SYSTEM=YES

The service provider then sets its address space AX to a value of 1. An AX value of 1 authorizes the service provider to issue a PT or SSAR instruction to all other address spaces. (Because the service provider is providing a service to all users, the service provider does not need to obtain a unique AX.)

         LA     2,1
         AXSET  AX=(2)

The service provider then issues the ETCRE macro to create the entry table.

         ETCRE  ENTRIES=ETDESC
         ST     0,TKVALUE          SAVE THE ET TOKEN

The service provider can construct the PC numbers and make them accessible the same way it did in Example 1 - Making services available to selected address spaces.