Forking is the only way new processes are created.
The
flags
argument to
rfork
selects which resources of the
invoking process (parent) are shared
by the new process (child) or initialized to
their default values.
The resources include
the file name space,
the open file descriptor table (which, when shared, permits processes
to open and close files for other processes),
the set of environment variables
(see
env(3)),
the note group
(the set of processes that receive notes written to a member's
notepg
file;
see
proc(3)),
the set of rendezvous tags
(see
rendezvous(2));
and open files.
Flags
is the logical OR of some subset of
- RFPROC
- If set a new process is created; otherwise changes affect the
current process.
- RFNOWAIT
- If set, the child process will be dissociated from the parent. Upon
exit the child will leave no
Waitmsg
(see
wait(2))
for the parent to collect.
- RFNAMEG
- If set, the new process inherits a copy of the parent's name space;
otherwise the new process shares the parent's name space.
Is mutually exclusive with
RFCNAMEG.
- RFCNAMEG
- If set, the new process starts with a clean name space. A new
name space must be built from a mount of an open file descriptor.
Is mutually exclusive with
RFNAMEG.
- RFNOMNT
- If set, subsequent mounts into the new name space and dereferencing
of pathnames starting with
#
are disallowed.
- RFENVG
- If set, the environment variables are copied;
otherwise the two processes share environment variables.
Is mutually exclusive with
RFCENVG.
- RFCENVG
- If set, the new process starts with an empty environment.
Is mutually exclusive with
RFENVG.
- RFNOTEG
- Each process is a member of a group of processes that all
receive notes when a note is written to any of their
notepg
files (see
proc(3)).
The group of a new process is by default the same as its parent, but if
RFNOTEG
is set (regardless of
RFPROC),
the process becomes the first in a new group, isolated from
previous processes.
- RFFDG
- If set, the invoker's file descriptor table (see
intro(2))
is copied; otherwise the two processes share a
single table.
- RFCFDG
- If set, the new process starts with a clean file descriptor table.
Is mutually exclusive with
RFFDG.
- RFREND
- If set, the process will be unable to
rendezvous(2)
with any of its ancestors; its children will, however, be able to
rendezvous
with it. In effect,
RFREND
makes the process the first in a group of processes that share a space for
rendezvous
tags.
- RFMEM
- If set, the child and the parent will share
data
and
bss
segments.
Otherwise, the child inherits a copy of those segments.
Other segment types, in particular stack segments, will be unaffected.
May be set only with
RFPROC.
File descriptors in a shared file descriptor table are kept
open until either they are explicitly closed
or all processes sharing the table exit.
If
RFPROC
is set, the
value returned in the parent process
is the process id
of the child process; the value returned in the child is zero.
Without
RFPROC,
the return value is zero.
Process ids range from 1 to the maximum integer
(int)
value.
Rfork
will sleep, if necessary, until required process resources are available.
Fork
is just a call of
rfork(RFFDG|RFREND|RFPROC).