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.\"	$NetBSD: _lwp_create.2,v 1.7 2017/04/23 11:38:53 wiz Exp $
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.\" Copyright (c) 2003 The NetBSD Foundation, Inc.
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe of Wasabi Systems, Inc.
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.Dd April 21, 2017
.Dt _LWP_CREATE 2
.Os
.Sh NAME
.Nm _lwp_create
.Nd create a new light-weight process
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In lwp.h
.Ft int
.Fn _lwp_create "ucontext_t *context" "unsigned long flags" "lwpid_t *new_lwp"
.Sh DESCRIPTION
.Fn _lwp_create
causes creation of a new light-weight process, or LWP, and adds it to the
current process.
The
.Fa context
argument specifies the initial execution context for the new LWP including
signal mask, stack, and machine registers.
The signal stack of the newly created light-weight process is reset to
disabled.
If this context specifies invalid register values (for example priviledge
escalation by setting machine dependend bits forbidden for user processes),
or does not specify cpu register values (uc_flags does not have the
_UC_CPU bit set), the call will fail and errno will be set to EINVAL.
.Pp
The following flags affect the creation of the new LWP:
.Bl -tag -width LWP_SUSPENDED
.It LWP_DETACHED
The LWP is created detached.
The resources associated with a detached LWP will be automatically
reclaimed by the system when the LWP exits.
Otherwise, a terminated LWP's resources will not be reclaimed until
its status is reported to another LWP via
.Xr _lwp_wait 2 .
.It LWP_SUSPENDED
The LWP is created suspended, and will not begin execution until
it is resumed by another LWP via
.Xr _lwp_continue 2 .
.\" __LWP_ASLWP is not yet implemented by the NetBSD kernel.
.El
.Pp
The LWP ID of the new LWP is stored in the location pointed to by
.Fa new_lwp .
.Sh RETURN VALUES
Upon successful completion,
.Fn _lwp_create
returns a value of 0.
Otherwise, a value of -1 is returned and errno is set to one of the values
documented below.
.Sh ERRORS
.Fn _lwp_create
will fail and no LWP will be created if:
.Bl -tag -width 10n
.It Bq Er EAGAIN
The system-imposed limit on the total
number of LWPs under execution would be exceeded.
This limit is configuration-dependent.
.It Bq Er EFAULT
The address pointed to by
.Fa context
or
.Fa new_lwp
is outside the process's allocated address space.
.It Bq Er EINVAL
The ucontext_t passed is invalid.
.It Bq Er ENOMEM
There is insufficient swap space for the new LWP.
.El
.Sh SEE ALSO
.Xr _lwp_continue 2 ,
.Xr _lwp_exit 2 ,
.Xr _lwp_wait 2 ,
.Xr _lwp_makecontext 3
.Sh HISTORY
The
.Fn _lwp_create
system call first appeared in
.Nx 2.0 .