Mainframe Call Generator (MCG) Refresh - Micro Focus

Mainframe Call Generator Refresh
Termination of misbehaving MCG programs
No restrictions are placed on the MCG RPC program logic and it is possible for a program to loop
or enter a WAIT that will never be satisfied. In these cases, the end user only sees that the client
is busy with a remote program call. Eventually, the client will be interrupted by a communications
timeout and close the TCP/IP stream socket connection to the server.
In previous implementations of the MCG RPC function (both Mainframe Access Version 2 and the
original MFA Server Version 3), the socket close would not be recognized at the server. This is
because the user program is in control of the task execution (either looping or waiting) and the
server logic does not receive control to process communications events.
In the new design, the user program execution in the MCGEXEC task is separated from the
communications processing that now continues normally in the multi-threaded XDBMFADM task.
MFA Server can respond to the client’s socket close and log the user off. The logoff cleanup
processing for the user’s Mainframe Access session recognizes that a MCG subtask is still
allocated to the user, and can force it down using the z/OS CALLRTM service to ABEND the
subtask. The subtask is unconditionally ended with a User 201 ABEND code in this case. The
end user can also force a program out using the “stop debugging” action before the expiration of
the timeout period.
The following excerpt from a test system shows a program starting at 14:40:53.2 hours. This test
program enters an endless loop of processing and waiting. The MFE timeout value (a Windows
environment variable) used in this test was set at 100 seconds and the socket connection was
closed due to a communications error (a timeout) exactly 100 seconds later, at 14:42:33.2 hours.
Message MFM0131E is issued during the cleanup processing to log the forced termination of the
MCGEXEC task with a U201 ABEND.
14:40:53.2 MCGEXEC 20 TMCGTEST - Input test name is "LOOP "
14:42:33.2 XDBMFADM 19 MFM0112I SAF logoff for CSIRLW1 (sd=8 (13EDA970) rc=0 type=0)
14:42:33.3 XDBMFADM 19 MFADirect close for sd=8 (13EDA970) ip=10.10.1.7 sent=8 rcvd=9
14:42:33.3 XDBMFADM 19 MFM0131E Task MCGEXEC 13E99E28 TCB 008B7280 terminated U0201;
callrtm rc=000
Many cases of incorrect MCG program execution can be recognized and cleaned up using this
forced termination. However, there are no restrictions placed on the user program and a MCG
program can possibly damage the server address space in such a way that simple task
termination fails to provide adequate cleanup. For example, the program can overlay server
control blocks and data areas, allocate excessive virtual storage without releasing it at the
conclusion of processing, consume address space and/or system resources without releasing,
etc. It is also possible for incorrect MCG program execution to cause the server address space to
fail without warning. In all cases of program failure and recovery (that is what the forced
termination actually is), it is advisable to shutdown and restart the server at the earliest
convenient time.
Confidential - 12 - December 2004
Randy Witek
Micro Focus Development