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Rfork is a partial implementation of the Plan 9 system call. It
can be used to manipulate some process state and to create new
processes a la fork(2). It cannot be used to create shared-memory
processes (Plan 9’s RFMEM flag); for that functionality use proccreate
(see thread(3)).
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. 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(3))
for the parent to collect.
RFNOTEG Each process is a member of a group of processes that all
receive notes when a note is sent to the group (see postnote(3)
and signal(2)). 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. In Plan
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9, a process can call rfork(RFNOTEG) and then be sure that it
will no longer receive console interrupts or other notes. Unix
job-control shells put each command in its own process group and
then relay notes to the current foreground command, making the
idiom less useful.
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RFFDG If set, the invoker’s file descriptor table (see intro())
is copied; otherwise the two processes share a single table.
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.
Calling rfork(RFFDG|RFPROC) is equivalent to calling fork(2).
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