man-pages/man3/sigset.3

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.\" Copyright (c) 2005 by Michael Kerrisk <mtk-manpages@gmx.net>
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.TH SIGSET 3 2005-12-01 "Linux 2.6.14" "Linux Programmer's Manual"
.SH NAME
sigset, sighold, sigrelse, sigignore \- System V signal API
.SH SYNOPSIS
.B #define _XOPEN_SOURCE 500
.br
.B #include <signal.h>
.sp
.B typedef void (*sighandler_t)(int);
.sp
.BI "sighandler_t sigset(int " sig ", sighandler_t " disp );
.sp
.BI "int sighold(int " sig );
.sp
.BI "int sigrelse(int " sig );
.sp
.BI "int sigignore(int " sig );
.SH DESCRIPTION
These functions are provided in glibc as a compatibility interface
for programs that make use of the historical System V signal API.
This API is obsolete: new applications should use the POSIX signal API
.RB ( sigaction (2),
.BR sigprocmask (2),
etc.)

The
.BR sigset ()
function modifies the disposition of the signal
.IR sig .
The
.I disp
argument can be the address of a signal handler function,
or one of the following constants:
.TP
.BR SIG_DFL
Reset the disposition of
.I sig
to the default.
.TP
.BR SIG_IGN
Ignore
.IR sig .
.TP
.BR SIG_HOLD
Add
.I sig
to the process's signal mask, but leave the disposition of
.I sig
unchanged.
.PP
If
.I disp
specifies the address of a signal handler, then
.I sig
is added to the process's signal mask during execution of the handler.
.PP
If
.I disp
was specified as a value other than
.BR SIG_HOLD ,
then
.I sig
is removed from the process's signal mask.
.PP
The dispositions for
.B SIGKILL
and
.B SIGSTOP
cannot be changed.
.PP
The
.BR sighold ()
function adds
.I sig
to the calling process's signal mask.

The
.BR sigrelse ()
function removes
.I sig
from the calling process's signal mask.

The
.BR sigignore ()
function sets the disposition of
.I sig
to
.BR SIG_IGN .
.SH RETURN VALUE
On success,
.BR sigset ()
returns
.B SIG_HOLD
if
.I sig
was blocked before the call,
or the signal's previous disposition
if it was not blocked before the call.
On error,
.BR sigset ()
returns \-1, with
.I errno
set to indicate the error.
.\" FIXME But as at 2.3.5, glibc's sigset() is broken for the
.\" SIG_HOLD case: it will only return SIG_HOLD if 'disp' is
.\" SIG_HOLD; if the signal is blocked, then sigset() should return
.\" SIG_HOLD even if 'disp' is specified as something other than
.\" SIG_HOLD (I have tested this on Solaris 8 and HP-UX 11).
.\" -- mtk, 29 Nov 05
.\" See http://sourceware.org/bugzilla/show_bug.cgi?id=1951
.\" 24 Apr 06: According to Ulrich Drepper the problem is now fixed.
.\" 4 Jul 06: Looking at the 20060626 glibc tree, the problem is fixed,
.\" but the fix is not yet in a 2.4.x release.

The
.BR sighold (),
.BR sigrelse (),
and
.BR sigignore ()
functions return 0 on success; on error, these functions return \-1 and set
.I errno
to indicate the error.
.SH ERRORS
For
.BR sigset ()
see the ERRORS under
.BR sigaction (2)
and
.BR sigprocmask (2).

For
.BR sighold ()
and
.BR sigrelse ()
see the ERRORS under
.BR sigprocmask (2).

For
.BR sigignore (),
see the errors under
.BR sigaction (2).
.SH NOTES
These functions appeared in glibc version 2.1.

The
.I sighandler_t
type is a GNU extension; it is only used on this page to make the
.BR sigset ()
prototype more easily readable.

The
.BR sigset ()
function provides reliable signal handling semantics (as when calling
.BR sigaction (2)
with
.I sa_mask
equal to 0).

On System V, the
.BR signal ()
function provides unreliable semantics (as when calling
.BR sigaction (2)
with
.I sa_mask
equal to
.IR "SA_RESETHAND | SA_NODEFER" ).
On BSD,
.BR signal ()
provides reliable semantics.
POSIX.1-2001 leaves these aspects of
.BR signal ()
unspecified.
See
.BR signal (2)
for further details.

In order to wait for a signal,
BSD and System V both provided a function named
.BR sigpause (),
but this function has a different argument on the two systems.
See
.BR sigpause (3)
for details.
.SH BUGS
In versions of glibc before 2.2,
.BR sigset ()
did not unblock
.I sig
if
.I disp
was specified as a value other than
.BR SIG_HOLD .

In all versions of glibc up to and including 2.3.5,
.BR sigset ()
does not correctly return the previous disposition of the signal
in two cases.
First, if
.I disp
is specified as
.BR SIG_HOLD ,
then a successful
.BR sigset ()
always returns
.BR SIG_HOLD .
Instead, it should return the previous disposition of the signal
(unless the signal was blocked, in which case
.BR SIG_HOLD
should be returned).
Second, if the signal is currently blocked, then
the return value of a successful
.BR sigset ()
should be
.BR SIG_HOLD .
Instead, the previous disposition of the signal is returned.
.\"FIXME This has been reported on 30 Nov 05 -- mtk
.\" See http://sourceware.org/bugzilla/show_bug.cgi?id=1951
.\"
.\" The POSIX.1-2001 disposition of sigset() says:
.\"     Upon successful completion, sigset() shall return
.\"     SIG_HOLD if the signal had been blocked and the signal's
.\"     previous disposition if it had not been blocked.
.\"     Otherwise, SIG_ERR shall be returned and errno set to
.\"     indicate the error.
.SH "CONFORMING TO"
SVr4, POSIX.1-2001.
These functions are obsolete: do not use them in new programs.
.SH "SEE ALSO"
.BR kill (2),
.BR pause (2),
.BR sigaction (2),
.BR signal (2),
.BR sigprocmask (2),
.BR raise (3),
.BR sigpause (3),
.BR sigvec (3),
.BR feature_test_macros (7),
.BR signal (7)