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	1	.\" Copyright (c) 1985, 1991, 1993
	2	.\" The Regents of the University of California. All rights reserved.
	3	.\"
	4	.\" Redistribution and use in source and binary forms, with or without
	5	.\" modification, are permitted provided that the following conditions
	6	.\" are met:
	7	.\" 1. Redistributions of source code must retain the above copyright
	8	.\" notice, this list of conditions and the following disclaimer.
	9	.\" 2. Redistributions in binary form must reproduce the above copyright
	10	.\" notice, this list of conditions and the following disclaimer in the
	11	.\" documentation and/or other materials provided with the distribution.
	12	.\" 4. Neither the name of the University nor the names of its contributors
	13	.\" may be used to endorse or promote products derived from this software
	14	.\" without specific prior written permission.
	15	.\"
	16	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	17	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	18	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	19	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	20	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	21	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	22	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	23	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	24	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	25	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	26	.\" SUCH DAMAGE.
	27	.\"
	28	.\" @(#)siginterrupt.3 8.1 (Berkeley) 6/4/93
	29	.\" $FreeBSD: src/lib/libc/gen/siginterrupt.3,v 1.15 2007/01/09 00:27:55 imp Exp $
	30	.\"
	31	.Dd June 4, 1993
	32	.Dt SIGINTERRUPT 3
	33	.Os
	34	.Sh NAME
	35	.Nm siginterrupt
	36	.Nd allow signals to interrupt system calls
	37	.Sh LIBRARY
	38	.Lb libc
	39	.Sh SYNOPSIS
	40	.In signal.h
	41	.Ft int
	42	.Fn siginterrupt "int sig" "int flag"
	43	.Sh DESCRIPTION
	44	The
	45	.Fn siginterrupt
	46	function
	47	is used to change the system call restart
	48	behavior when a system call is interrupted by the specified signal.
	49	If the flag is false (0), then system calls will be restarted if
	50	they are interrupted by the specified signal
	51	and no data has been transferred yet.
	52	System call restart has been the default behavior since
	53	.Bx 4.2 ,
	54	and is the default behaviour for
	55	.Xr signal 3
	56	on
	57	.Fx .
	58	.Pp
	59	If the flag is true (1),
	60	then restarting of system calls is disabled.
	61	If a system call is interrupted by the specified signal
	62	and no data has been transferred,
	63	the system call will return \-1 with the global variable
	64	.Va errno
	65	set to
	66	.Er EINTR .
	67	Interrupted system calls that have started transferring
	68	data will return the amount of data actually transferred.
	69	System call interrupt is the signal behavior found on
	70	.Bx 4.1
	71	and
	72	.At V
	73	systems.
	74	.Pp
	75	Note that the new
	76	.Bx 4.2
	77	signal handling semantics are not
	78	altered in any other way.
	79	Most notably, signal handlers always remain installed until
	80	explicitly changed by a subsequent
	81	.Xr sigaction 2
	82	call, and the signal mask operates as documented in
	83	.Xr sigaction 2 .
	84	Programs may switch between restartable and interruptible
	85	system call operation as often as desired in the execution of a program.
	86	.Pp
	87	Issuing a
	88	.Fn siginterrupt 3
	89	call during the execution of a signal handler will cause
	90	the new action to take place on the next signal to be caught.
	91	.Sh NOTES
	92	This library routine uses an extension of the
	93	.Xr sigaction 2
	94	system call that is not available in
	95	.Bx 4.2 ;
	96	hence, it should not be used if backward compatibility is needed.
	97	.Sh RETURN VALUES
	98	.Rv -std siginterrupt
	99	.Sh ERRORS
	100	The
	101	.Fn siginterrupt
	102	call fails if:
	103	.Bl -tag -width Er
	104	.It Bq Er EINVAL
	105	The
	106	.Fa sig
	107	argument
	108	is not a valid signal number.
	109	.El
	110	.Sh SEE ALSO
	111	.Xr sigaction 2 ,
	112	.Xr sigblock 2 ,
	113	.Xr sigpause 2 ,
	114	.Xr sigsetmask 2 ,
	115	.Xr signal 3
	116	.Sh HISTORY
	117	The
	118	.Fn siginterrupt
	119	function appeared in
	120	.Bx 4.3 .