Asynchronous cross memory POST

The POST macro signifies the completion of an event by one routine to another. Usually the system posts the completion of the event in the user's address space. The user can, however, cause the system to post completion of the event in another address space.

The authorized user (executing in supervisor state, under protection key 0-7, or APF-authorized) of the POST macro can use the ASCB and ERRET parameters to perform a POST in an address space other than the user's own. If the caller is authorized to specify the ASCB and ERRET parameters, no check is made to determine if the requested address space is the issuing address space. This use of the POST macro is sometimes known as “asynchronous cross memory post”.

Note: Do not issue asynchronous cross memory Post more frequently than necessary. Large numbers of cross memory Posts can consume excessive amounts of system resources.

The ERRET routine is given control when POST detects an error after control has been returned to the issuer of POST. If the ERRET routine does not functionally need to do anything, use CVTBRET or CVTRCZRT in the CVT data area as the ERRET routine.