Ubuntu Manpage: sigevent, sigval - structure for notification from asynchronous routines

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:

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