mirror of https://github.com/mkerrisk/man-pages
250 lines
6.7 KiB
Groff
250 lines
6.7 KiB
Groff
.\" Copyright (c) 2002 Michael Kerrisk <mtk.manpages@gmail.com>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.TH SIGWAITINFO 2 2017-09-15 "Linux" "Linux Programmer's Manual"
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.SH NAME
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sigwaitinfo, sigtimedwait, rt_sigtimedwait \- synchronously wait
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for queued signals
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.SH SYNOPSIS
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.nf
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.B #include <signal.h>
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.PP
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.BI "int sigwaitinfo(const sigset_t *" set ", siginfo_t *" info ");"
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.PP
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.BI "int sigtimedwait(const sigset_t *" set ", siginfo_t *" info ,
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.BI " const struct timespec *" timeout ");"
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.fi
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.PP
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.RS -4
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.RE
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.PP
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.BR sigwaitinfo (),
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.BR sigtimedwait ():
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_POSIX_C_SOURCE\ >=\ 199309L
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.SH DESCRIPTION
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.BR sigwaitinfo ()
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suspends execution of the calling thread until one of the signals in
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.I set
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is pending
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(If one of the signals in
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.I set
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is already pending for the calling thread,
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.BR sigwaitinfo ()
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will return immediately.)
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.PP
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.BR sigwaitinfo ()
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removes the signal from the set of pending
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signals and returns the signal number as its function result.
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If the
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.I info
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argument is not NULL,
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then the buffer that it points to is used to return a structure of type
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.I siginfo_t
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(see
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.BR sigaction (2))
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containing information about the signal.
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.PP
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If multiple signals in
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.I set
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are pending for the caller, the signal that is retrieved by
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.BR sigwaitinfo ()
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is determined according to the usual ordering rules; see
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.BR signal (7)
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for further details.
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.PP
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.BR sigtimedwait ()
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operates in exactly the same way as
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.BR sigwaitinfo ()
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except that it has an additional argument,
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.IR timeout ,
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which specifies the interval for which
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the thread is suspended waiting for a signal.
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(This interval will be rounded up to the system clock granularity,
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and kernel scheduling delays mean that the interval
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may overrun by a small amount.)
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This argument is of the following type:
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.PP
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.in +4n
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.EX
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struct timespec {
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long tv_sec; /* seconds */
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long tv_nsec; /* nanoseconds */
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}
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.EE
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.in
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.PP
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If both fields of this structure are specified as 0, a poll is performed:
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.BR sigtimedwait ()
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returns immediately, either with information about a signal that
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was pending for the caller, or with an error
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if none of the signals in
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.I set
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was pending.
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.SH RETURN VALUE
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On success, both
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.BR sigwaitinfo ()
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and
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.BR sigtimedwait ()
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return a signal number (i.e., a value greater than zero).
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On failure both calls return \-1, with
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.I errno
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set to indicate the error.
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.SH ERRORS
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.TP
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.B EAGAIN
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No signal in
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.I set
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was became pending within the
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.I timeout
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period specified to
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.BR sigtimedwait ().
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.TP
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.B EINTR
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The wait was interrupted by a signal handler; see
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.BR signal (7).
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(This handler was for a signal other than one of those in
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.IR set .)
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.TP
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.B EINVAL
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.I timeout
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was invalid.
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008.
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.SH NOTES
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In normal usage, the calling program blocks the signals in
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.I set
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via a prior call to
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.BR sigprocmask (2)
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(so that the default disposition for these signals does not occur if they
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become pending between successive calls to
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.BR sigwaitinfo ()
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or
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.BR sigtimedwait ())
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and does not establish handlers for these signals.
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In a multithreaded program,
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the signal should be blocked in all threads, in order to prevent
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the signal being treated according to its default disposition in
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a thread other than the one calling
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.BR sigwaitinfo ()
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or
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.BR sigtimedwait ()).
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.PP
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The set of signals that is pending for a given thread is the
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union of the set of signals that is pending specifically for that thread
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and the set of signals that is pending for the process as a whole (see
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.BR signal (7)).
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.PP
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Attempts to wait for
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.B SIGKILL
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and
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.B SIGSTOP
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are silently ignored.
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.PP
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If multiple threads of a process are blocked
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waiting for the same signal(s) in
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.BR sigwaitinfo ()
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or
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.BR sigtimedwait (),
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then exactly one of the threads will actually receive the
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signal if it becomes pending for the process as a whole;
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which of the threads receives the signal is indeterminate.
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.PP
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.BR sigwaitinfo ()
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or
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.BR sigtimedwait (),
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can't be used to receive signals that
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are synchronously generated, such as the
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.BR SIGSEGV
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signal that results from accessing an invalid memory address
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or the
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.BR SIGFPE
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signal that results from an arithmetic error.
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Such signals can be caught only via signal handler.
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.PP
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POSIX leaves the meaning of a NULL value for the
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.I timeout
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argument of
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.BR sigtimedwait ()
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unspecified, permitting the possibility that this has the same meaning
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as a call to
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.BR sigwaitinfo (),
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and indeed this is what is done on Linux.
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.\"
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.SS C library/kernel differences
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On Linux,
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.BR sigwaitinfo ()
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is a library function implemented on top of
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.BR sigtimedwait ().
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.PP
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The glibc wrapper functions for
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.BR sigwaitinfo ()
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and
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.BR sigtimedwait ()
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silently ignore attempts to wait for the two real-time signals that
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are used internally by the NPTL threading implementation.
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See
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.BR nptl (7)
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for details.
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.PP
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The original Linux system call was named
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.BR sigtimedwait ().
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However, with the addition of real-time signals in Linux 2.2,
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the fixed-size, 32-bit
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.I sigset_t
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type supported by that system call was no longer fit for purpose.
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Consequently, a new system call,
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.BR rt_sigtimedwait (),
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was added to support an enlarged
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.IR sigset_t
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type.
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The new system call takes a fourth argument,
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.IR "size_t sigsetsize" ,
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which specifies the size in bytes of the signal set in
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.IR set .
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This argument is currently required to have the value
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.IR sizeof(sigset_t)
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(or the error
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.B EINVAL
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results).
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The glibc
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.BR sigtimedwait ()
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wrapper function hides these details from us, transparently calling
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.BR rt_sigtimedwait ()
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when the kernel provides it.
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.\"
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.SH SEE ALSO
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.BR kill (2),
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.BR sigaction (2),
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.BR signal (2),
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.BR signalfd (2),
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.BR sigpending (2),
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.BR sigprocmask (2),
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.BR sigqueue (3),
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.BR sigsetops (3),
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.BR sigwait (3),
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.BR signal (7),
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.BR time (7)
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