CLU comparison (function code X'04')

The following parameters follow the CLU search exit parameter list header when the logon manager receives a session request and needs to compare contending CLUs to determine which CLU is best to service the session. See Criteria for contending CLUs for more information about the selection algorithm the sample exit uses to choose the best CLU.

If there is only one contending CLU, the exit is called with information about only that CLU. If there is more than one contending CLU, the exit compares them a pair at a time. In each iteration, the exit selects the better of the two CLUs to be the current best CLU. In the first iteration, the current best CLU is the first contending CLU the logon manager encounters. In each subsequent iteration, the exit compares the current best CLU from the previous iteration to another contending CLU. The exit continues to compare pairs of CLUs until there are no more contending CLUs. At that point, the exit returns the name of the better CLU from the final iteration to the logon manager as the best CLU. If no best CLU is found after the list of possible CLUs is exhausted, the session request fails.

Within the function code X'04' parameters, the description of the contending CLU is always presented between hex 48 and hex 7F. The description of the current best CLU is always presented between hex 80 and hex B8. If the exit determines the contending CLU is the better of two CLUs, the contender CLU's values are moved to hex 80 and it becomes the current best CLU. If only one CLU is presented to the CLU search exit, the description of that CLU is presented between hex 80 and hex B8. If two CLUs are equal in comparison, there is no move and the CLU search exit chooses the CLU described between hex 80 and hex B8.

Table 1. Function code X'04' parameters
Dec (Hex) offset	Size (Bytes)	Description
8 (8)	4	Reserved
12 (C)	1	Reserved
13 (D)	1	Retry indicator B'1... ....' If this indicator is turned on, the session request is being tried again. The remaining bits are reserved.
14 (E)	2	Reserved
16 (10)	8	If the retry indicator is turned on, this is the name of the CLU that was unable to establish a session in the most recent session attempt.
24 (18)	8	Class-of-service name for this session
32 (20)	8	Reserved
40 (28)	8	Session partner name This is the name of the resource that will be in session with this TPF. This is the DLU if the session request was initiated by TPF; otherwise, this is the OLU.
48 (30)	4	Session partner subarea This is the subarea address of the boundary function for the session partner as known in the network where the logon manager resides.
52 (34)	8	Generic TPF application program name
60 (3C)	4	Reserved
64 (40)	4	Application program user extension control block pointer
68 (44)	4	The number of links currently supporting the application program
72 (48)	8	The name of the new contending CLU
80 (50)	8	Reserved
88 (58)	8	The name of the application program LU
96 (60)	4	Parallel session count This is the number of active parallel sessions currently serviced by the contending CLU.
100 (64)	4	CLU user extension control block pointer This pointer provides access to the control block for the contending CLU.
104 (68)	4	Session count This is the number of active sessions currently serviced by the contending CLU.
108 (6C)	4	Sessions pending This is the number of pending sessions to be serviced by the contending CLU.
112 (70)	4	Session limit This is the maximum number of sessions the contending CLU can support.
116 (74)	4	Hop count This is the number of hops from the OLU to TPF.
120 (78)	4	Subarea address of the contending CLU's boundary function
124 (7C)	1	Host of the contending CLU
125 (7D)	3	Reserved
128 (80)	8	The name of the current best CLU
136 (88)	8	Reserved
144 (90)	8	The name of the application program LU
152 (98)	4	Parallel session count This is the number of active parallel sessions currently serviced by the current best CLU.
156 (9C)	4	CLU user extension control block pointer This pointer provides access to the control block for the current best CLU.
160 (A0)	4	Session count This is the number of active sessions currently serviced by the current best CLU.
164 (A4)	4	Sessions pending This is the number of pending sessions to be serviced by the current best CLU.
168 (A8)	4	Session limit This is the maximum number of sessions the current best CLU can support.
172 (AC)	4	Hop count This is the number of hops from the OLU to TPF.
176 (B0)	4	Subarea address of the current best CLU's boundary function
180 (B4)	1	Host of the current best CLU
181 (B5)	3	Reserved

Note: If you create any of the user extension control blocks (logon manager vector table user extension, CLU user extension, or application program user extension), begin the control block with a 4-byte reserved field followed by a 2-byte length field.