Linux man pages

Section (7) sigevent

Linux manual pages	Section 7

Name

sigevent — structure for notification from asynchronous routines

Synopsis

#include <signal.h>

union	sigval {			/* Data passed with notification */
	int		`sival_int`;	/* Integer value */
	void	*	`sival_ptr`;	/* Pointer value */
};

struct	sigevent {
	int		`sigev_notify`;	/* Notification method */
	int		`sigev_signo`;	/* Notification signal */
	union sigval		`sigev_value`;	/* Data passed with notification */
	void	(*	`sigev_notify_function`)(union sigval);	/* Function used for thread notification (SIGEV_THREAD) */
	void	*	`sigev_notify_attributes`;	/* Attributes for notification thread (SIGEV_THREAD) */
	pid_t		`sigev_notify_thread_id`;	/* ID of thread to signal (SIGEV_THREAD_ID) */
};

DESCRIPTION

The sigevent structure is used by various APIs to describe the way a process is to be notified about an event (e.g., completion of an asynchronous request, expiration of a timer, or the arrival of a message).

The definition shown in the SYNOPSIS is approximate: some of the fields in the sigevent structure may be defined as part of a union. Programs should employ only those fields relevant to the value specified in sigev_notify.

The sigev_notify field specifies how notification is to be performed. This field can have one of the following values:

SIGEV_NONE

A null notification: don_zsingle_quotesz_t do anything when the event occurs.

SIGEV_SIGNAL

Notify the process by sending the signal specified in sigev_signo.

If the signal is caught with a signal handler that was registered using the sigaction(2) SA_SIGINFO flag, then the following fields are set in the siginfo_t structure that is passed as the second argument of the handler:

si_code

This field is set to a value that depends on the API delivering the notification.

si_signo

This field is set to the signal number (i.e., the same value as in sigev_signo).

si_value

This field is set to the value specified in sigev_value.

Depending on the API, other fields may also be set in the siginfo_t structure.

The same information is also available if the signal is accepted using sigwaitinfo(2).

SIGEV_THREAD

Notify the process by invoking sigev_notify_function as if it were the start function of a new thread. (Among the implementation possibilities here are that each timer notification could result in the creation of a new thread, or that a single thread is created to receive all notifications.) The function is invoked with sigev_value as its sole argument. If sigev_notify_attributes is not NULL, it should point to a pthread_attr_t structure that defines attributes for the new thread (see pthread_attr_init(3)).

SIGEV_THREAD_ID (Linux-specific)

Currently used only by POSIX timers; see timer_create(2).

COLOPHON

This page is part of release 4.16 of the Linux 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/.

  Copyright (C) 2006, 2010 Michael Kerrisk <mtk.manpagesgmail.com>
Copyright (C) 2009 Petr Baudis <paskysuse.cz>

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