mirror of https://github.com/mkerrisk/man-pages
sigevent.7: New page to centralize description of sigevent structure
Several interfaces use this structure. Best to centralize the common details in one place. Content taken from the existing timerfd_create.2 and mq_open.3 pages, with additions by Petr Baudis and Michael Kerrisk. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Copyright (C) 2006, 2010 Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Copyright (C) 2009 Petr Baudis <pasky@suse.cz>
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.\"
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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.\" manual page may be incorrect or out-of-date.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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.\"
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.TH SIGEVENT 7 2010-09-19 "GNU" "Linux Programmer's Manual"
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.SH NAME
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struct sigevent \- structure for notification from asynchronous routines
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.SH SYNOPSIS
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.nf
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union sigval { /* Data passed with notification */
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int sival_int; /* Integer value */
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void *sival_ptr; /* Pointer value */
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};
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struct sigevent {
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int sigev_notify; /* Notification method */
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int sigev_signo; /* Notification signal */
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union sigval sigev_value; /* Data passed with
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notification */
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void (*sigev_notify_function) (union sigval);
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/* Function used for thread
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notification (SIGEV_THREAD) */
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void *sigev_notify_attributes;
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/* Attributes for notification thread
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(SIGEV_THREAD) */
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pid_t sigev_notify_thread_id;
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/* ID of thread to signal (SIGEV_THREAD_ID) */
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};
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.fi
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.SH DESCRIPTION
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.PP
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The
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.I sigevent
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structure is used by various APIs
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to describe the way a process is to be notified about an event
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(e.g., completion of an asynchronous request, expiration of a timer,
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or the arrival of a message).
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.PP
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The definition shown in the SYNOPSIS is approximate:
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some of the fields in the
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.I sigevent
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structure may be defined as part of a union.
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Programs should only employ those fields relevant
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to the value specified in
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.IR sigev_notify .
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.PP
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The
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.I sigev_notify
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field specifies how notification is to be performed.
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This field can have one of the following values:
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.TP 8
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.BR SIGEV_NONE
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A "null" notification: don't do anything when the event occurs.
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.TP
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.BR SIGEV_SIGNAL
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Notify the process by sending the signal specified in
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.IR sigev_signo .
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.IP
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If the signal is caught with a signal handler that was registered using the
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.BR sigaction (2)
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.B SA_SIGINFO
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flag, then the following fields are set in the
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.I siginfo_t
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structure that is passed as the second argument of the handler:
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.RS 8
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.TP 10
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.I si_code
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This field is set to a value that depends on the API
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delivering the notification.
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.TP
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.I si_signo
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This field is set to the signal number (i.e., the same value as in
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.IR sigev_signo ).
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.TP
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.I si_value
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This field is set to the value specified in
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.IR sigev_value .
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.RE
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.IP
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Depending on the API, other fields may also be set in the
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.I siginfo_t
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structure.
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.IP
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The same information is also available if the signal is accepted using
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.BR sigwaitinfo (2).
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.TP
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.BR SIGEV_THREAD
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Notify the process by invoking
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.I sigev_notify_function
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"as if" it were the start function of a new thread.
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(Among the implementation possibilities here are that
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each timer notification could result in the creation of a new thread,
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or that a single thread is created to receive all notifications.)
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The function is invoked with
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.I sigev_value
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as its sole argument.
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If
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.I sigev_notify_attributes
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is not NULL, it should point to a
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.I pthread_attr_t
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structure that defines attributes for the new thread (see
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.BR pthread_attr_init (3)).
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.TP
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.BR SIGEV_THREAD_ID " (Linux-specific)"
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.\" | SIGEV_SIGNAL vs not?
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Currently used only by POSIX timers; see
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.BR timer_create (2).
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.SH CONFORMING TO
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POSIX.1-2001.
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.SH "SEE ALSO"
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.BR timer_create (2),
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.BR aio_fsync (3),
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.\" .BR lio_listio (3),
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.\" FIXME This page will be added later .BR getaddrinfo_a (3),
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.BR mq_notify (3),
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.BR pthreads (7)
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