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sigevent(3type) sigevent(3type)

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 */
    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 */
};

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:

A "null" notification: don't do anything when the event occurs.
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:
This field is set to a value that depends on the API delivering the notification.
This field is set to the signal number (i.e., the same value as in sigev_signo).
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).
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)).
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>.

SEE ALSO

timer_create(2), getaddrinfo_a(3), lio_listio(3), mq_notify(3), pthread_sigqueue(3), sigqueue(3), aiocb(3type), siginfo_t(3type)

2025-05-17 Linux man-pages (unreleased)