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man/man3/rfork.3
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man/man3/rfork.3
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.TH RFORK 3
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.SH NAME
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rfork \- manipulate process state
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.nf
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.B
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int rfork(int flags)
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.fi
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.SH DESCRIPTION
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.I Rfork
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is a partial implementation of the Plan 9 system call.
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It can be used to manipulate some process state and to create
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new processes a la
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.IR fork (2).
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It cannot be used to create shared-memory processes
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(Plan 9's
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.B RFMEM
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flag); for that functionality use
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.I proccreate
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(see
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.IR thread (3)).
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.PP
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The
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.I flags
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argument to
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.I rfork
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selects which resources of the
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invoking process (parent) are shared
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by the new process (child) or initialized to
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their default values.
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.I Flags
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is the logical OR of some subset of
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.TF RFCNAMEG
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.TP
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.B RFPROC
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If set a new process is created; otherwise changes affect the
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current process.
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.TP
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.B RFNOWAIT
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If set, the child process will be dissociated from the parent. Upon
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exit the child will leave no
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.B Waitmsg
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(see
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.IR wait (3))
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for the parent to collect.
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.\" .TP
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.\" .B RFNAMEG
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.\" If set, the new process inherits a copy of the parent's name space;
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.\" otherwise the new process shares the parent's name space.
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.\" Is mutually exclusive with
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.\" .BR RFCNAMEG .
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.\" .TP
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.\" .B RFCNAMEG
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.\" If set, the new process starts with a clean name space. A new
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.\" name space must be built from a mount of an open file descriptor.
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.\" Is mutually exclusive with
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.\" .BR RFNAMEG .
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.\" .TP
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.\" .B RFNOMNT
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.\" If set, subsequent mounts into the new name space and dereferencing
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.\" of pathnames starting with
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.\" .B #
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.\" are disallowed.
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.\" .TP
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.\" .B RFENVG
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.\" If set, the environment variables are copied;
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.\" otherwise the two processes share environment variables.
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.\" Is mutually exclusive with
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.\" .BR RFCENVG .
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.\" .TP
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.\" .B RFCENVG
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.\" If set, the new process starts with an empty environment.
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.\" Is mutually exclusive with
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.\" .BR RFENVG .
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.TP
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.B RFNOTEG
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Each process is a member of a group of processes that all
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receive notes when a note is sent to the group
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(see
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.IR postnote (3)
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and
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.IR signal (2)).
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The group of a new process is by default the same as its parent, but if
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.B RFNOTEG
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is set (regardless of
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.BR RFPROC ),
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the process becomes the first in a new group, isolated from
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previous processes.
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In Plan 9, a process can call
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.B rfork(RFNOTEG)
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and then be sure that it will no longer receive console interrupts
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or other notes.
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Unix job-control shells put each command in its own process group
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and then relay notes to the current foreground command, making
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the idiom less useful.
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.TP
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.B RFFDG
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If set, the invoker's file descriptor table (see
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.IR intro ( ))
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is copied; otherwise the two processes share a
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single table.
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.\" .TP
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.\" .B RFCFDG
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.\" If set, the new process starts with a clean file descriptor table.
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.\" Is mutually exclusive with
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.\" .BR RFFDG .
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.\" .TP
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.\" .B RFREND
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.\" If set, the process will be unable to
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.\" .IR rendezvous (3)
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.\" with any of its ancestors; its children will, however, be able to
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.\" .B rendezvous
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.\" with it. In effect,
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.\" .B RFREND
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.\" makes the process the first in a group of processes that share a space for
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.\" .B rendezvous
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.\" tags.
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.\" .TP
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.\" .B RFMEM
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.\" If set, the child and the parent will share
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.\" .B data
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.\" and
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.\" .B bss
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.\" segments.
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.\" Otherwise, the child inherits a copy of those segments.
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.\" Other segment types, in particular stack segments, will be unaffected.
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.\" May be set only with
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.\" .BR RFPROC .
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.PD
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.PP
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File descriptors in a shared file descriptor table are kept
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open until either they are explicitly closed
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or all processes sharing the table exit.
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.PP
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If
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.B RFPROC
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is set, the
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value returned in the parent process
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is the process id
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of the child process; the value returned in the child is zero.
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Without
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.BR RFPROC ,
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the return value is zero.
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Process ids range from 1 to the maximum integer
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.RB ( int )
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value.
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.I Rfork
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will sleep, if necessary, until required process resources are available.
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.PP
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Calling
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.B rfork(RFFDG|RFPROC)
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is equivalent to calling
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.IR fork (2).
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.SH SOURCE
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.B /usr/local/plan9/src/lib9/rfork.c
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.SH DIAGNOSTICS
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.I Rfork
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sets
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.IR errstr .
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