For the data space interface, the read queue exit routine is entered when VTAM CMIP services needs to notify the application program that:

• There are messages on the data space to be read
• CMIP services is terminating
• The data space is full

The requirements for callers of the read queue exit routine are:

Location

User private

Key

Same key that was used when the MIBConnect function was called

State

Supervisor state

AMODE

31-bit

Residency mode

Any

ASC mode

Primary

Interrupt status

Enabled

Dispatchable unit mode

TCB

Locks

No locks held

ENQs

No ENQs held

@space

Same address space from which MIBConnect was issued

The data passed to the read queue exit routine is located in CSA storage and is allocated in the same key that was used when the MIBConnect function was called. The data is not fetch protected, so any key can be used to copy it. The read queue exit routine should not attempt to free any storage passed to it. Storage is freed automatically when the exit routine terminates. Application programs can vary depending on product data and queuing structures. The following list gives recommendations for the read queue exit routine:

• Use the contents of the user data field located in register 6 to set up the environment. This field can be the address of an autodata area to improve performance, or it can be NULL.
• Save the calling application program's registers in the provided save area.
• Check the VTAM reason codes to determine why the exit routine was called and what action should be taken. For a list of reason codes, see VTAM reason codes (for data space) and VTAM reason codes (for CSA).