.\"	$NetBSD: _lwp_create.2,v 1.11 2022/12/04 16:17:50 uwe Exp $
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.\" 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 privilege
escalation by setting machine dependent bits forbidden for user processes),
or does not specify cpu register values
.Fa ( uc_flags
does not have the
.Dv _UC_CPU
bit set), the call will fail and errno will be set to
.Er EINVAL .
.Pp
The following flags affect the creation of the new LWP:
.Bl -tag -width Dv
.It Dv 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 Dv 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
.Rv -std _lwp_create
.Sh ERRORS
.Fn _lwp_create
will fail and no LWP will be created if:
.Bl -tag -width Er
.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
.Vt 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 .