A new task is created by issuing an ATTACH, or, if your program runs in access register ASC mode, an ATTACHX macro. The task that is active when the ATTACH or ATTACHX is issued is the originating task; the newly created task is the subtask of the originating task. The subtask competes for control in the same manner as any other task in the system, on the basis of priority (both address space priority and task priority within the address space) and the current ability to use a processor. The address of the task control block for the subtask is returned in register 1.
If the ATTACH or ATTACHX executes successfully, control returns to the user with a return code of 0 in register 15.
The entry point in the load module to be given control when the subtask becomes active is specified as it is in a LINK or LINKX macro, that is, through the use of the EP, EPLOC, and DE parameters. The use of these parameters is discussed in Program management. You can pass parameters to the subtask using the PARAM and VL parameters, also described under the LINK macro. Additional parameters deal with the priority of the subtask, provide for communication between tasks, specify libraries to be used for program linkages, and establish an error recovery environment for the new subtask.