Replaceable routines

In addition to the REXX exits, TSO/E supplies replaceable routines you can use to customize REXX processing. For exec processing, various system services are used for loading and freeing execs, performing I/O, obtaining and freeing storage, and handling data stack requests. TSO/E provides routines that handle these types of system services, which you can replace. The names of the routines are defined in the module name table for each particular language processor environment. In non-TSO/E address spaces, you can provide your own replaceable routines. In the TSO/E address space, you can provide your own replaceable routines only if you initialize a language processor environment that is not integrated into TSO/E, that is, the TSOFL flag is off.

Your routine can check the request for a system service, change the request if needed, and then call the system-supplied routine to actually perform the service. Your routine can perform the request itself and not call the system-supplied routine. It can also terminate the request for a system service. You can specify the routine name either by:

Providing your own parameters module(s)
Calling the IRXINIT routine and passing the name of the routine on the call

Table 1 provides a brief description of the replaceable routines. They are described in detail in .

Table 1. Summary of replaceable routines
Replaceable routine	Description
Exec load	This routine is called to load an exec into storage and to free the exec when it is no longer needed.
Input/Output (I/O)	This routine is called to read a record from or write a record to a specified ddname. For example, this routine is called for the SAY instruction, the PULL instruction (when the data stack is empty), and for the EXECIO command. The routine is also called to open and close a data set.
Data stack	This routine is called to handle any requests for data stack services. For example, it is called for the PULL, PUSH, and QUEUE instructions and for the MAKEBUF and DROPBUF commands.
Storage management	This routine is called to obtain and free storage.
User ID	This routine is called to obtain the user ID or terminal ID. The result it obtains is returned by the USERID built-in function.
Message identifier	This routine determines if the message identifier (message ID) is displayed with a REXX error message.
Host command environment	This routine is called to handle the execution of host commands for a specific host command environment.