Reference Guide

ZCOM C I/F Library Routines
ZOPEN (3X)
Chapter 4270
ZOPEN (3X)
NAME zopen – Create ZLU program input queue
SYNOPSIS
#include <zcom/zcomsys.h>
#include <zcom/zcomcall.h> /* if compiled with ANSI C (recommended) */
int32 zopen (zap, pflag, name, limit)
zaddr_type *zap;
uint32 pflag;
char *name;
uint32 limit;
DESCRIPTION Routine zopen allocates a free ZLU as a program input queue. This must
be done before a program may receive any messages from terminals or
other programs. The calling program’s PID is put into the zowner field of
the zlu_type structure.
If a calling program (or thread) terminates without doing a zclos(3X) of a
ZLU, that ZLU and its resources will remain allocated in the ZCOM
system. When the program (or thread) is restarted later on, that ZLU
can be re-opened (using the same name parameter) without losing its
queue contents. The program (or thread) can re-use the ZLU and resume
its processing from where it left off. To flush the contents of a re-opened
ZLU, use the zqmve(3X) routine after the ZLU is opened.
If it is not desirable to re-use an existing ZLU, the ZCOM_ZOPEN_NEW
bit of pflag can be set. In this case, if the ZLU name already exists, the
ZLU is not re-opened and error ZENAME (-11) is returned.
A ZLU can be defined either as a primary or an auxiliary ZLU. Auxiliary
ZLUs are used, for example, when a program is receiving messages from
multiple sources, so that the messages can be read in a different order
from which they were received. All programs must have a primary ZLU
defined, because all status messages are returned to the primary ZLU.
In addition, a program’s primary ZLU is used as the source ZLU for
messages sent by that program (unless overridden by a different ZLU
specified in the message header). Refer to the zsend(3X) routine for
details.