sigevent(7)
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_SIGINFOflag, 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). - If the signal is caught with a signal handler that was registered using the
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)
Colophon
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