TS/MP Pathsend and Server Programming Manual (G06.24+, H06.03+)

Writing Pathsend Requesters
NonStop TS/MP Pathsend and Server Programming Manual–132500
3-2
Interprocess Communication in the Pathsend
Environment
Interprocess Communication in the Pathsend
Environment
Communication between requesters and servers in the Pathsend environment differs
from communication between Guardian requesters and servers. Rather than directly
opening a particular server process, the requester opens the LINKMON process, which
in turn opens a server process selected by the PATHMON process. The LINKMON
process’s open of the server process is shared among all requesters running in the same
processor as the LINKMON process.
The communication begins as follows:
1. The requester calls a Pathsend procedure (for example, SERVERCLASS_SEND_)
to request a server-class send operation.
2. The request goes to the LINKMON process running in the same processor as the
Pathsend requester process.
3. The LINKMON process checks for a link to a server process in the server class
specified in the request. If the LINKMON process has no available link to the server
class, the actions performed depend on the settings of the PATHMON configuration
parameters NUMSTATIC and MAXLINKS. The following steps might occur:
a. The LINKMON process sends a “get-link” request to the PATHMON process
that manages the server class specified in the procedure call.
b. The PATHMON process selects a server process in the specified server class. If
necessary, it starts and initializes a new server process in the server class.
c. The PATHMON process sends back to the LINKMON process the Guardian
process name of a server process within the specified server class.
d. The LINKMON process opens the server process of that name. This open is
shared among all the Pathsend requester processes running in the same
processor as that LINKMON process; therefore, a close operation does not
necessarily occur when the communication with a particular requester process is
finished.
For more information about the NUMSTATIC and MAXLINKS parameters and
their effects on get-link requests, refer to the NonStop TS/MP System Management
Manual.
4. The LINKMON process forwards the send request to the server process.
5. When the server process replies, the LINKMON process replies to the requester
process, and the server-class send operation is complete.
The action of the PATHMON process in step 3 is called granting a link. The LINKMON
process, which requests links and provides access to the server process after the link is
granted, is called the link manager. (For SCREEN COBOL requesters, the terminal
control process (TCP) serves as the link manager.)