sigevent - structure for notification from asynchronous routines
#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) */
};
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).
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)