-.\" Copyright (c) 2002 Michael kerrisk <mtk16@ext.canterbury.ac.nz>
+.\" Copyright (c) 2002 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
+.\" %%%LICENSE_START(VERBATIM)
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.\" preserved on all copies.
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein.
+.\" the use of the information contained herein. The author(s) may not
+.\" have taken the same level of care in the production of this manual,
+.\" which is licensed free of charge, as they might when working
+.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
-.TH SIGWAITINFO 2 2002-06-07 "Linux 2.4.18" "Linux Programmer's Manual"
+.TH SIGWAITINFO 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
-sigwaitinfo, sigtimedwait \- synchronously wait for queued signals
+sigwaitinfo, sigtimedwait, rt_sigtimedwait \- synchronously wait
+for queued signals
.SH SYNOPSIS
+.nf
.B #include <signal.h>
-.sp
+.PP
.BI "int sigwaitinfo(const sigset_t *" set ", siginfo_t *" info ");"
-.sp
+.PP
.BI "int sigtimedwait(const sigset_t *" set ", siginfo_t *" info ", "
-.BI "const struct timespec " timeout ");"
+.BI " const struct timespec *" timeout ");"
+.fi
+.PP
+.in -4n
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.in
+.PP
+.BR sigwaitinfo (),
+.BR sigtimedwait ():
+_POSIX_C_SOURCE\ >=\ 199309L
.SH DESCRIPTION
.BR sigwaitinfo ()
-suspends execution of the calling process until one of the signals in
+suspends execution of the calling thread until one of the signals in
.I set
-is delivered.
+is pending
(If one of the signals in
.I set
-is already pending for the calling process,
+is already pending for the calling thread,
.BR sigwaitinfo ()
-will return immediately with information about that signal.)
-
+will return immediately.)
+.PP
.BR sigwaitinfo ()
-removes the delivered signal from the calling process's list of pending
+removes the signal from the set of pending
signals and returns the signal number as its function result.
If the
.I info
-argument is not
-.BR NULL ,
-then it returns a structure of type
+argument is not NULL,
+then the buffer that it points to is used to return a structure of type
.I siginfo_t
(see
.BR sigaction (2))
containing information about the signal.
.PP
-Signals returned via
+If multiple signals in
+.I set
+are pending for the caller, the signal that is retrieved by
.BR sigwaitinfo ()
-are delivered in the usual order; see
+is determined according to the usual ordering rules; see
.BR signal (7)
for further details.
.PP
.BR sigwaitinfo ()
except that it has an additional argument,
.IR timeout ,
-which enables an upper bound to be placed on the time for which
-the process is suspended.
+which specifies the interval for which
+the thread is suspended waiting for a signal.
+(This interval will be rounded up to the system clock granularity,
+and kernel scheduling delays mean that the interval
+may overrun by a small amount.)
This argument is of the following type:
-.sp
-.in +2n
-.nf
+.PP
+.in +4n
+.EX
struct timespec {
long tv_sec; /* seconds */
long tv_nsec; /* nanoseconds */
}
-.fi
-.in -2n
-.sp
+.EE
+.in
+.PP
If both fields of this structure are specified as 0, a poll is performed:
.BR sigtimedwait ()
returns immediately, either with information about a signal that
if none of the signals in
.I set
was pending.
-.SH "RETURN VALUE"
+.SH RETURN VALUE
On success, both
.BR sigwaitinfo ()
and
.B EAGAIN
No signal in
.I set
-was delivered within the
+was became pending within the
.I timeout
period specified to
.BR sigtimedwait ().
.TP
.B EINTR
-The wait was interrupted by a signal handler.
+The wait was interrupted by a signal handler; see
+.BR signal (7).
(This handler was for a signal other than one of those in
.IR set .)
.TP
.B EINVAL
.I timeout
was invalid.
+.SH CONFORMING TO
+POSIX.1-2001, POSIX.1-2008.
.SH NOTES
-In normal usage, the caller blocks the signals in
+In normal usage, the calling program blocks the signals in
.I set
via a prior call to
-.BR sigprocmask ()
+.BR sigprocmask (2)
(so that the default disposition for these signals does not occur if they
-are delivered between successive calls to
-.BR sigwaitinfo () or
-.BR sigtimedwait())
+become pending between successive calls to
+.BR sigwaitinfo ()
+or
+.BR sigtimedwait ())
and does not establish handlers for these signals.
+In a multithreaded program,
+the signal should be blocked in all threads, in order to prevent
+the signal being treated according to its default disposition in
+a thread other than the one calling
+.BR sigwaitinfo ()
+or
+.BR sigtimedwait ()).
+.PP
+The set of signals that is pending for a given thread is the
+union of the set of signals that is pending specifically for that thread
+and the set of signals that is pending for the process as a whole (see
+.BR signal (7)).
+.PP
+Attempts to wait for
+.B SIGKILL
+and
+.B SIGSTOP
+are silently ignored.
.PP
-POSIX leaves the meaning of a
-.B NULL
-value for the
+If multiple threads of a process are blocked
+waiting for the same signal(s) in
+.BR sigwaitinfo ()
+or
+.BR sigtimedwait (),
+then exactly one of the threads will actually receive the
+signal if it becomes pending for the process as a whole;
+which of the threads receives the signal is indeterminate.
+.PP
+.BR sigwaitinfo ()
+or
+.BR sigtimedwait (),
+can't be used to receive signals that
+are synchronously generated, such as the
+.BR SIGSEGV
+signal that results from accessing an invalid memory address
+or the
+.BR SIGFPE
+signal that results from an arithmetic error.
+Such signals can be caught only via signal handler.
+.PP
+POSIX leaves the meaning of a NULL value for the
.I timeout
argument of
.BR sigtimedwait ()
as a call to
.BR sigwaitinfo (),
and indeed this is what is done on Linux.
-.SH "CONFORMING TO"
-POSIX 1003.1-2001
-.SH "SEE ALSO"
+.\"
+.SS C library/kernel differences
+On Linux,
+.BR sigwaitinfo ()
+is a library function implemented on top of
+.BR sigtimedwait ().
+.PP
+The glibc wrapper functions for
+.BR sigwaitinfo ()
+and
+.BR sigtimedwait ()
+silently ignore attempts to wait for the two real-time signals that
+are used internally by the NPTL threading implementation.
+See
+.BR nptl (7)
+for details.
+.PP
+The original Linux system call was named
+.BR sigtimedwait ().
+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_sigtimedwait (),
+was added to support an enlarged
+.IR sigset_t
+type.
+The new system call takes a fourth argument,
+.IR "size_t sigsetsize" ,
+which specifies the size in bytes of the signal set in
+.IR set .
+This argument is currently required to have the value
+.IR sizeof(sigset_t)
+(or the error
+.B EINVAL
+results).
+The glibc
+.BR sigtimedwait ()
+wrapper function hides these details from us, transparently calling
+.BR rt_sigtimedwait ()
+when the kernel provides it.
+.\"
+.SH SEE ALSO
.BR kill (2),
.BR sigaction (2),
.BR signal (2),
+.BR signalfd (2),
.BR sigpending (2),
.BR sigprocmask (2),
-.BR sigqueue (2),
+.BR sigqueue (3),
.BR sigsetops (3),
-.BR signal (7)
+.BR sigwait (3),
+.BR signal (7),
+.BR time (7)
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