When a REXX exec is executing in either a user server or a scheduler address space, the following REXX commands are available, addressing the REXX exec environment (see SA22-7790-xx: TSO/E REXX Reference):
f <scheduler|userserver>,REXX,{HI|HT|RT|TS},SUBTASK={x|ALL}
The abbreviations stand for
Parameter subtask specifies the number of the worker task (T000000x). There are at most NUMTCB worker tasks. Specifying ALL would address all worker tasks simultaneously.