When you connect to the list structure and indicate your interest in using the list transition monitoring function, the system allocates a list notification vector for your use and returns a token to you representing this vector. The list notification vector shows the state (empty or non-empty) of each list you are monitoring. Each connector to the list structure that indicates interest in list monitoring (by coding the VECTORLEN parameter on the IXLCONN macro) is allocated a list notification vector.

A list notification vector consists of an array of entries in which each entry is logically associated with a list in the structure. The number of entries must be a multiple of 32.

When a list transition occurs for a monitored list, the system automatically updates the associated entry in the list notification vector to reflect the empty or nonempty state of the list. The IXLVECTR macro provides the interface to the list notification vector. To determine whether a list you are monitoring is empty or non-empty, invoke the IXLVECTR macro with either the TESTLISTSTATE or LTVECENTRIES parameter. You can use the IXLVECTR macro with the MODIFYVECTORSIZE parameter to change the size of your list notification vector, so you can monitor more lists, for instance. See Using the IXLVECTR Macro for more information.