sigevent(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); Linux-specific */
};

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'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).

SEE ALSO
timer_create(2), aio_fsync(3), aio_read(3), aio_write(3), getaddrinfo_a(3), lio_listio(3), mq_notify(3), aio(7), pthreads(7)