SNAX/APC Management Programming Manual

2 Communicating With the
SNAX/APC Process
111813 Tandem Computers Incorporated 2–1
SNAX/APC subsystem commands are processed and responses are generated by the
SNAX/APC process. However, DSM applications do not communicate directly with
the SNAX/APC process. DSM applications send requests to the SCP, which then
routes the SCP requests to the correct process. In the case of SNAX/APC, this is done
by opening the process with the qualifier #ZSPI, (such as $snax/apc-process.#ZSPI)
where $snax/apc-process is the name of the SNAX/APC process.
This section describes the issues involved in using the SCP to communicate with the
SNAX/APC process.
Communicating
With SCP
Your DSM applications do not communicate directly with the SNAX/APC subsystem;
instead, applications communicate with the SCP. To send commands to and receive
responses from the SNAX/APC subsystem, applications use the file system to open
and send requests to the SCP.
The following steps outline how a DSM application communicates with SCP; the
SNAX/APC process must have been created before these steps can be performed.
1. The DSM application opens the SCP process, $ZNET, with the qualifier #ZSPI
($ZNET.#ZSPI).
2. The application sends an SPI-formatted request (a SNAX/APC programmatic
command) to the SCP, and uses either the manager token, ZSPI-TKN-MANAGER,
or the object-name token, ZCOM-TKN-OBJNAME, to determine the destination
subsystem. The manager token is not required if an application specifies an object-
name token; however, an application must specify one or the other.
In most cases, SCP uses ZCOM-TKN-OBJNAME to determine the SNAX/APC
destination process; however, when a command addresses the NULL object type,
ZSPI-TKN-MANAGER is used to provide the SNAX/APC process name. The SPI
Programming Manual describes SPI and SPI-formatted requests.
3. The SCP checks whether it has the appropriate SNAX/APC process open; if not,
the SCP opens the process with the #ZSPI qualifier ($snax/apc-process.#ZSPI).
4. The SCP checks whether or not the versions of the SNAX/APC process and the
DSM application are compatible, and it performs security validation on the
request.
5. If all is well, the SCP forwards the request to the SNAX/APC process.
6. The SNAX/APC process returns its responses to the SCP; the SCP then returns
the responses to the DSM application.
7. Before terminating, the application closes the $ZNET process.
Usually, the SNAX/APC process remains in the OPEN state after being opened by the
SCP. It will be closed if any file-system error occurs or at the expiration of any timeout
value. The SPI Common Extensions Manual describes communications with the SCP in
detail.