.\" Copyright (c) 2007 The DragonFly Project.  All rights reserved.
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.\" This code is derived from software contributed to The DragonFly Project
.\" by Simon 'corecode' Schubert <corecode@fs.ei.tum.de>
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.\" $DragonFly: src/lib/libc/sys/lwp_create.2,v 1.1 2007/03/12 21:06:18 corecode Exp $
.\"
.Dd March 12, 2007
.Dt LWP_CREATE 2
.Os
.Sh NAME
.Nm lwp_create
.Nd spawn a new lwp
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn lwp_create "struct lwp_params *params"
.Sh DESCRIPTION
The
.Fn lwp_create
function is used to spawn a new lwp in the current process.
In some way, this is like
.Xr fork 2 ,
however
.Fn lwp_create
does not return twice as parent and child.
Instead, the new lwp will start running a function which
is provided with the parameters
.Fa params ,
as outlined below.
.Bd -literal
struct lwp_params {
	void (*func)(void *);	/* Function to start execution */
	void *arg;		/* Parameter to this function */
	void *stack;		/* Stack address to use */
	lwpid_t *tid1;		/* Address to copy out new tid */
	lwpid_t *tid2;		/* Same */
};
.Ed
.Pp
The
.Fa params
passed to
.Fn lwp_create
are as follows.
Set
.Fa func
to specify the function to be executed in the new lwp.
It is the duty of
.Fa func
to terminate
execution of the lwp correctly, either by calling
.Xr extexit 2
or
.Xr exit 3 .
If the
.Fa func
simply returns, behavior is unspecified.
The only function argument passed to
.Fa func
is
.Fa arg .
.Pp
The new lwp starts out with its stack frame set to
.Fa stack .
This parameter, like
.Fa func
is mandatory.  If any of these is invalid, behavior is
unspecified.
.Pp
The fields
.Fa tid1
and
.Fa tid2
point to variables where the tid of the new lwp should be stored.
There are two parameters so that storage for both parent
and child can be specified separately.  Set any of these fields to
NULL in case you don't need the tid to be copied out.
.Sh RETURN VALUES
Upon successful completion, the value 0 is returned;
otherwise the value -1 is returned and
.Va errno
will be set to
.Er EINVAL .
.Sh SEE ALSO
.Xr extexit 2 ,
.Xr rfork 2 ,
.Xr exit 3
.Sh HISTORY
The
.Fn lwp_create
function first appeared in
.Dx 1.9 .