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	1	.\" Copyright (c) 2002 Packet Design, LLC.
	2	.\" All rights reserved.
	3	.\"
	4	.\" Subject to the following obligations and disclaimer of warranty,
	5	.\" use and redistribution of this software, in source or object code
	6	.\" forms, with or without modifications are expressly permitted by
	7	.\" Packet Design; provided, however, that:
	8	.\"
	9	.\" (i) Any and all reproductions of the source or object code
	10	.\" must include the copyright notice above and the following
	11	.\" disclaimer of warranties; and
	12	.\" (ii) No rights are granted, in any manner or form, to use
	13	.\" Packet Design trademarks, including the mark "PACKET DESIGN"
	14	.\" on advertising, endorsements, or otherwise except as such
	15	.\" appears in the above copyright notice or in the software.
	16	.\"
	17	.\" THIS SOFTWARE IS BEING PROVIDED BY PACKET DESIGN "AS IS", AND
	18	.\" TO THE MAXIMUM EXTENT PERMITTED BY LAW, PACKET DESIGN MAKES NO
	19	.\" REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING
	20	.\" THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED
	21	.\" WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE,
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	23	.\" OR MAKE ANY REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS
	24	.\" OF THE USE OF THIS SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY,
	25	.\" RELIABILITY OR OTHERWISE. IN NO EVENT SHALL PACKET DESIGN BE
	26	.\" LIABLE FOR ANY DAMAGES RESULTING FROM OR ARISING OUT OF ANY USE
	27	.\" OF THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY DIRECT,
	28	.\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR CONSEQUENTIAL
	29	.\" DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, LOSS OF
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	31	.\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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	35	.\"
	36	.\" $FreeBSD: src/lib/libc/gen/getcontext.3,v 1.3 2004/12/03 14:10:04 rse Exp $
	37	.\"
	38	.Dd September 10, 2002
	39	.Dt GETCONTEXT 3
	40	.Os
	41	.Sh NAME
	42	.Nm getcontext , setcontext
	43	.Nd get and set user thread context
	44	.Sh LIBRARY
	45	.Lb libc
	46	.Sh SYNOPSIS
	47	.In ucontext.h
	48	.Ft int
	49	.Fn getcontext "ucontext_t *ucp"
	50	.Ft int
	51	.Fn setcontext "const ucontext_t *ucp"
	52	.Sh DESCRIPTION
	53	The
	54	.Fn getcontext
	55	function
	56	saves the current thread's execution context in the structure pointed to by
	57	.Fa ucp .
	58	This saved context may then later be restored by calling
	59	.Fn setcontext .
	60	.Pp
	61	The
	62	.Fn setcontext
	63	function
	64	makes a previously saved thread context the current thread context, i.e.,
	65	the current context is lost and
	66	.Fn setcontext
	67	does not return.
	68	Instead, execution continues in the context specified by
	69	.Fa ucp ,
	70	which must have been previously initialized by a call to
	71	.Fn getcontext ,
	72	.Xr makecontext 3 ,
	73	or by being passed as an argument to a signal handler (see
	74	.Xr sigaction 2 ) .
	75	.Pp
	76	If
	77	.Fa ucp
	78	was initialized by
	79	.Fn getcontext ,
	80	then execution continues as if the original
	81	.Fn getcontext
	82	call had just returned (again).
	83	.Pp
	84	If
	85	.Fa ucp
	86	was initialized by
	87	.Xr makecontext 3 ,
	88	execution continues with the invocation of the function specified to
	89	.Xr makecontext 3 .
	90	When that function returns,
	91	.Fa "ucp->uc_link"
	92	determines what happens next:
	93	if
	94	.Fa "ucp->uc_link"
	95	is
	96	.Dv NULL ,
	97	the process exits;
	98	otherwise,
	99	.Fn setcontext "ucp->uc_link"
	100	is implicitly invoked.
	101	.Pp
	102	If
	103	.Fa ucp
	104	was initialized by the invocation of a signal handler, execution continues
	105	at the point the thread was interrupted by the signal.
	106	.Sh RETURN VALUES
	107	If successful,
	108	.Fn getcontext
	109	returns zero and
	110	.Fn setcontext
	111	does not return; otherwise \-1 is returned.
	112	.Sh ERRORS
	113	No errors are defined for
	114	.Fn getcontext
	115	or
	116	.Fn setcontext .
	117	.Sh SEE ALSO
	118	.Xr sigaction 2 ,
	119	.Xr sigaltstack 2 ,
	120	.Xr makecontext 3 ,
	121	.Xr ucontext 3