COBOL Manual for TNS and TNS/R Programs

Process Initiation, Communication, and
Management
HP COBOL Manual for TNS and TNS/R Programs—522555-006
31-17
At-End Condition
•
SYNCDEPTH
Usually set to 1 for Pathway servers unless they are multithreaded.
•
REPLY CONTAINS
Specifies the length of the reply that the server sends back to the requester. It
specifies the name of the file containing the longest record that is used as a reply
or an explicit number of characters.
At-End Condition
An entry is made in the receive-control table when a requester executes an OPEN for
a file assigned to the server process. A requester can have more than one OPEN
issued to a server process at any given time. The receive-control table has a separate
entry for each of these OPENs.
An entry is deleted from the receive-control table whenever the requester issues a
CLOSE for the file assigned to the server process. A server continues to receive
requester messages through $RECEIVE if there is an entry in the table. When the last
entry is deleted, an at-end condition arises for the server’s READ statement.
This at-end condition is handled as an end of file for $RECEIVE. If a file status code
data item is defined, it is set to “10” (EOF). Control passes to the statement in the AT
END phrase or to a USE procedure if no AT END phrase is present. If the server is a
Pathway server, it must stop itself when it detects an at-end condition.
An attempt to read a file when it is at end of file causes a permanent error, setting the
file status code to “30.” Ordinarily, the program must close and reopen the file before
any further activity is possible on that file. For $RECEIVE, however, the run-time
routines simulate a close/open sequence, relieving the program of this responsibility;
however, such a READ after end of file should include a TIME LIMIT phrase, or the
READ could wait indefinitely. See READ for Sequential or Dynamic Access.
When a server process has just begun execution and no entries are yet in its receive-
control table, an at-end condition will never occur before the first OPEN message is
received.
Summary of $RECEIVE Rules
These rules apply to programs that use $RECEIVE:
•
Files assigned to $RECEIVE must be sequentially organized and not described
with alternate keys or LINAGE clauses.
•
A RECEIVE-CONTROL paragraph in the Input-Output Section of the Environment
Division is necessary to define two internal tables essential to the function of
$RECEIVE. (Although the RECEIVE-CONTROL paragraph is optional, the default
tables permit only the most limited use of $RECEIVE.)