sigval - structure for notification from asynchronous routines

NAME SYNOPSIS DESCRIPTION sigevent sigval STANDARDS HISTORY NOTES SEE ALSO

NAME

sigevent, sigval − structure for notification from asynchronous routines

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.