Section 3 · Library functions

sigval.3type

Package: man-pages

sigevent

NAME
SYNOPSIS
DESCRIPTION
STANDARDS
HISTORY
NOTES
SEE ALSO

NAME

sigevent, sigval − structure for notification from asynchronous routines

SYNOPSIS

#include <signal.h>

struct sigevent {
int sigev_notify; /* Notification type */ **
int sigev_signo;** /* Signal number */ **
union sigval sigev_value;** /* Data passed with notification */ **
void (*sigev_notify_function)(union sigval);**
/* Notification function
(SIGEV_THREAD) */ **
pthread_attr_t *sigev_notify_attributes;**
/* Notification attributes */
/* Linux only: */ **
pid_t sigev_notify_thread_id;**
/* ID of thread to signal
(SIGEV_THREAD_ID) */ **
};**

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

DESCRIPTION

sigevent

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’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).

sigval

Data passed with a signal.

STANDARDS

POSIX.1-2008.

HISTORY

POSIX.1-2001.

<aio.h> and <time.h> define sigevent since POSIX.1-2008.

NOTES

The following headers also provide sigevent: <aio.h>, <mqueue.h>, and <time.h>.