sigval(3type)

Usage

#include <signal.h>

struct sigevent { int sigev_notify; /* Notification type */ int sigev_signo; /* Signal number */ union sigval sigev_value; /* Data passed with notification */ typeof(void (union sigval)) *sigev_notify_function; /* 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 */ };

Overview

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.

Notes

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

Releases

3 releases since Debian 12 (Bookworm); the text changed 2 times.