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.TH BSD_SIGNAL 3 2019-03-06 "" "Linux Programmer's Manual"
.SH NAME
bsd_signal \- signal handling with BSD semantics
.SH SYNOPSIS
.B #include <signal.h>
.PP
.B typedef void (*sighandler_t)(int);
.PP
.BI "sighandler_t bsd_signal(int " signum ", sighandler_t " handler );
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.ad l
.BR bsd_signal ():
.RS 4
Since glibc 2.26:
    _XOPEN_SOURCE >= 500
.\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
        && ! (_POSIX_C_SOURCE\ >=\ 200809L)
.br
Glibc 2.25 and earlier:
    _XOPEN_SOURCE
.RE
.ad b
.SH DESCRIPTION
The
.BR bsd_signal ()
function takes the same arguments, and performs the same task, as
.BR signal (2).
.PP
The difference between the two is that
.BR bsd_signal ()
is guaranteed to provide reliable signal semantics, that is:
a) the disposition of the signal is not reset to the default
when the handler is invoked;
b) delivery of further instances of the signal is blocked while
the signal handler is executing; and
c) if the handler interrupts a blocking system call,
then the system call is automatically restarted.
A portable application cannot rely on
.BR signal (2)
to provide these guarantees.
.SH RETURN VALUE
The
.BR bsd_signal ()
function returns the previous value of the signal handler, or
.B SIG_ERR
on error.
.SH ERRORS
As for
.BR signal (2).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR bsd_signal ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
4.2BSD, POSIX.1-2001.
POSIX.1-2008 removes the specification of
.BR bsd_signal (),
recommending the use of
.BR sigaction (2)
instead.
.SH NOTES
Use of
.BR bsd_signal ()
should be avoided; use
.BR sigaction (2)
instead.
.PP
On modern Linux systems,
.BR bsd_signal ()
and
.BR signal (2)
are equivalent.
But on older systems,
.BR signal (2)
provided unreliable signal semantics; see
.BR signal (2)
for details.
.PP
The use of
.I sighandler_t
is a GNU extension;
this type is defined only if the
.B _GNU_SOURCE
feature test macro is defined.
.SH SEE ALSO
.BR sigaction (2),
.BR signal (2),
.BR sysv_signal (3),
.BR signal (7)
.SH COLOPHON
This page is part of release 5.04 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.