174 lines
3.8 KiB
Plaintext
174 lines
3.8 KiB
Plaintext
.TH FORK 2
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.SH NAME
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fork, rfork \- manipulate process resources
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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 fork(void)
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.PP
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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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Forking is the only way new processes are created.
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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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The resources include
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the file name space,
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the open file descriptor table (which, when shared, permits processes
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to open and close files for other processes),
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the set of environment variables
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(see
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.IR env (3)),
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the note group
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(the set of processes that receive notes written to a member's
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.B notepg
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file;
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see
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.IR proc (3)),
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the set of rendezvous tags
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(see
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.IR rendezvous (2));
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and open files.
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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 (2))
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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 are disallowed.
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All pathnames starting with
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.B #
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besides those used to access
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.IR pipe (3) ,
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.IR dup (3) ,
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.IR env (3) ,
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.IR cons (3) ,
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and
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.IR proc (3)
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can not be walked.
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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 written to any of their
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.B notepg
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files (see
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.IR proc (3)).
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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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.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 (2))
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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 (2)
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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 positive integer
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.RB ( int )
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value.
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.I Rfork
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may also return -1 if process resources are exhausted.
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.PP
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.I Fork
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is just a call of
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.BR rfork(RFFDG|RFREND|RFPROC) .
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.SH SOURCE
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.B /sys/src/libc/9syscall
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.br
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.B /sys/src/libc/9sys/fork.c
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.SH SEE ALSO
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.IR intro (2),
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.IR proc (3),
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.SH DIAGNOSTICS
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These functions set
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.IR errstr .
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