.\"	$OpenBSD: thread_fork.9,v 1.2 2017/02/15 03:33:13 guenther Exp $
.\"	$NetBSD: fork1.9,v 1.3 1999/03/16 00:40:47 garbled Exp $
.\"
.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
.\" NASA Ames Research Center.
.\"
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.\" modification, are permitted provided that the following conditions
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.Dd $Mdocdate: February 12 2017 $
.Dt THREAD_FORK 9
.Os
.Sh NAME
.Nm thread_fork
.Nd create a new thread inside a process
.Sh SYNOPSIS
.In sys/types.h
.In sys/proc.h
.Ft int
.Fo thread_fork
.Fa "struct proc *p1"
.Fa "void *stack"
.Fa "void *tcb"
.Fa "pid_t *tidptr"
.Fa "register_t *retval"
.Fc
.Sh DESCRIPTION
.Fn thread_fork
creates a new thread out of
.Ar p1 ,
which should be the current thread.
This function is used to implement the
.Xr __tfork 3
system call.
.Pp
.Fa stack ,
which must not be
.Dv NULL ,
will be used as the initial value of the new thread's stack pointer.
.Pp
If
.Fa tcb
is not
.Dv NULL ,
it will be used as the initial address of the new thread's TCB
(thread control block).
.Pp
If
.Fa tidptr
is not
.Dv NULL ,
the TID of the new thread will be copied out there on success.
This is guaranteed to be done before the new thread is started.
.Pp
On successful completion the TID of the new thread will be stored in
.Fa *retval .
.Sh RETURN VALUES
Upon successful completion of the operation,
.Fn thread_fork
returns 0.
Otherwise, the following error values are returned:
.Bl -tag -width [EAGAIN]
.It Bq Er EAGAIN
The system limit on the total number of threads would be exceeded.
.It Bq Er ENOMEM
There is insufficient swap space for the new thread.
.It Bq Er EINVAL
The
.Fa stack
argument was
.Dv NULL .
.El
.Sh SEE ALSO
.Xr __get_tcb 2 ,
.Xr fork 2 ,
.Xr __tfork 3 ,
.Xr tfind 9
.Sh HISTORY
The
.Fn thread_fork
function
appeared in
.Ox 6.1 .