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.\"     @(#)siginterrupt.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: head/lib/libc/gen/siginterrupt.3 207735 2010-05-06 22:49:54Z jilles $
.\"
.Dd June 4, 1993
.Dt SIGINTERRUPT 3
.Os
.Sh NAME
.Nm siginterrupt
.Nd allow signals to interrupt system calls
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.Ft int
.Fn siginterrupt "int sig" "int flag"
.Sh DESCRIPTION
The
.Fn siginterrupt
function
is used to change the system call restart
behavior when a system call is interrupted by the specified signal.
If the flag is false (0), then system calls will be restarted if
they are interrupted by the specified signal
and no data has been transferred yet.
System call restart has been the default behavior since
.Bx 4.2 ,
and is the default behaviour for
.Xr signal 3
on
.Fx .
.Pp
If the flag is true (1),
then restarting of system calls is disabled.
If a system call is interrupted by the specified signal
and no data has been transferred,
the system call will return \-1 with the global variable
.Va errno
set to
.Er EINTR .
Interrupted system calls that have started transferring
data will return the amount of data actually transferred.
System call interrupt is the signal behavior found on
.Bx 4.1
and
.At V
systems.
.Pp
Note that the new
.Bx 4.2
signal handling semantics are not
altered in any other way.
Most notably, signal handlers always remain installed until
explicitly changed by a subsequent
.Xr sigaction 2
call, and the signal mask operates as documented in
.Xr sigaction 2 .
Programs may switch between restartable and interruptible
system call operation as often as desired in the execution of a program.
.Pp
Issuing a
.Fn siginterrupt 3
call during the execution of a signal handler will cause
the new action to take place on the next signal to be caught.
.Sh NOTES
This library routine uses an extension of the
.Xr sigaction 2
system call that is not available in
.Bx 4.2 ,
hence it should not be used if backward compatibility is needed.
.Sh RETURN VALUES
.Rv -std siginterrupt
.Sh ERRORS
The
.Fn siginterrupt
call fails if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa sig
argument
is not a valid signal number.
.El
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr sigprocmask 2 ,
.Xr sigsuspend 2 ,
.Xr signal 3
.Sh HISTORY
The
.Fn siginterrupt
function appeared in
.Bx 4.3 .