System Grab Bag

Name

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 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

1. timer_create(2),
2. aio_fsync(3),
3. aio_read(3),
4. aio_write(3),
5. getaddrinfo_a(3),
6. lio_listio(3),
7. mq_notify(3),
8. aio(7),
9. pthreads(7)