.\" Copyright (c) 2005 Michael Kerrisk
.\" based on earlier work by faith@cs.unc.edu and
.\" Mike Battersby <mib@deakin.edu.au>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" 2005-09-15, mtk, Created new page by splitting off from sigaction.2
.\"
.TH sigsuspend 2 2023-03-30 "Linux man-pages 6.04"
.SH NAME
sigsuspend, rt_sigsuspend \- wait for a signal
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <signal.h>
.PP
.BI "int sigsuspend(const sigset_t *" mask );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR sigsuspend ():
.nf
    _POSIX_C_SOURCE
.fi
.SH DESCRIPTION
.BR sigsuspend ()
temporarily replaces the signal mask of the calling thread with the
mask given by
.I mask
and then suspends the thread until delivery of a signal whose
action is to invoke a signal handler or to terminate a process.
.PP
If the signal terminates the process, then
.BR sigsuspend ()
does not return.
If the signal is caught, then
.BR sigsuspend ()
returns after the signal handler returns,
and the signal mask is restored to the state before the call to
.BR sigsuspend ().
.PP
It is not possible to block
.B SIGKILL
or
.BR SIGSTOP ;
specifying these signals in
.IR mask ,
has no effect on the thread's signal mask.
.SH RETURN VALUE
.BR sigsuspend ()
always returns \-1, with
.I errno
set to indicate the error (normally,
.BR EINTR ).
.SH ERRORS
.TP
.B EFAULT
.I mask
points to memory which is not a valid part of the process address space.
.TP
.B EINTR
The call was interrupted by a signal;
.BR signal (7).
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.SS C library/kernel differences
The original Linux system call was named
.BR sigsuspend ().
However, with the addition of real-time signals in Linux 2.2,
the fixed-size, 32-bit
.I sigset_t
type supported by that system call was no longer fit for purpose.
Consequently, a new system call,
.BR rt_sigsuspend (),
was added to support an enlarged
.I sigset_t
type.
The new system call takes a second argument,
.IR "size_t sigsetsize" ,
which specifies the size in bytes of the signal set in
.IR mask .
This argument is currently required to have the value
.I sizeof(sigset_t)
(or the error
.B EINVAL
results).
The glibc
.BR sigsuspend ()
wrapper function hides these details from us, transparently calling
.BR rt_sigsuspend ()
when the kernel provides it.
.\"
.SH NOTES
Normally,
.BR sigsuspend ()
is used in conjunction with
.BR sigprocmask (2)
in order to prevent delivery of a signal during the execution of a
critical code section.
The caller first blocks the signals with
.BR sigprocmask (2).
When the critical code has completed, the caller then waits for the
signals by calling
.BR sigsuspend ()
with the signal mask that was returned by
.BR sigprocmask (2)
(in the
.I oldset
argument).
.PP
See
.BR sigsetops (3)
for details on manipulating signal sets.
.SH SEE ALSO
.BR kill (2),
.BR pause (2),
.BR sigaction (2),
.BR signal (2),
.BR sigprocmask (2),
.BR sigwaitinfo (2),
.BR sigsetops (3),
.BR sigwait (3),
.BR signal (7)