A single program can activate more than one ESTAE-type recovery routine by issuing the ESTAE or ESTAEX macro more than once with the CT parameter. The program can also overlay recovery routines by issuing ESTAE or ESTAEX with the OV parameter, or deactivate recovery routines by issuing ESTAE or ESTAEX with an address of zero.
ESTAE-type recovery routines get control in LIFO order, so the last ESTAE-type recovery routine activated is the first to get control. Remember that ESTAE-type recovery routines include ESTAE and ESTAEX routines, and ESTAI routines. ESTAI routines are entered after all other ESTAE-type recovery routines that exist for a given task have received control and have either failed or percolated.
MVS™ functions provide their own recovery routines; thus, percolation can pass control to both installation-written and system-provided recovery routines. If all recovery routines percolate -- that is, no recovery routine can recover from the error -- then the task is terminated.
When a recovery routine gets control and cannot recover from the error (that is, it does not retry), it must free the resources held by the mainline routine and request that the system continue with error processing (percolate). Note that a recovery routine entered with the SDWACLUP bit set to one, indicating that retry is not permitted, has no choice but to percolate. When the recovery routine requests percolation, the previously activated recovery routine gets control. When a retry is not requested and the system has entered all possible recovery routines, the task ends abnormally.
When a recovery routine requests percolation, it is deactivated; that is, it can no longer get control for this error. A deactivated recovery routine is not entered again unless that recovery routine is activated again after a retry.