.help zmain May84 "System Interface"
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NAME
zmain -- process main
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SYNOPSIS
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not applicable
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DESCRIPTION
The process main is the procedure or code segment which first gains control
when a process is executed by the host system.  The process main must determine
whether the process was called as a connected subprocess, as a detached process,
or by the host system.  If spawned as a connected subprocess the standard input
and output of the process are connected to IPC channels leading to the parent
process, otherwise the devices to which the process channels are connected are
machine dependent.

After connecting the process standard input, standard output, and standard
error output \fBzmain\fR calls the IRAF Main, an SPP procedure.
The calling sequence of the IRAF Main is as follows:

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	main (inchan, outchan, driver, prtype, bkgfile, jobcode)

	int	inchan		# standard input channel
	int	outchan		# standard output channel
	int	driver		# EPA of device driver for channels
	int	prtype		# process type code
	packed	char bkgfile[]	# name of bkgfile, if detached process
	int	jobcode		# bkg jobcode, if detached process
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The IPC driver, text file driver, and binary file driver are resident in
every process.  The \fBdriver\fR argument is the entry point address of
the read primitive of the appropriate driver, as returned by \fBzlocpr\fR.
The process type code is selected from the following:

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	PR_CONNECTED	1	# connected subprocess
	PR_DETACHED	2	# detached subprocess
	PR_HOST		3	# process run from host
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The process type determines the type of protocol to be used by the IRAF Main.
The background file and jobcode are used only if the process was spawned as
a detached process.
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RETURN VALUE
None.
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NOTES
Currently only the CL may be run as a detached process, and only ordinary
SPP processes may be run as connected subprocesses.  Either may be run directly
by the host system.  The CL uses a nonstandard Main.  Error recovery is
handled entirely by the IRAF Main.
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SEE ALSO
zfiopr, zfiotx, and the discussion of the process and IRAF mains in the
reference manual.
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