sigevent(7) - Linux man page

Name

sigevent - structure for notification from asynchronous routines

Synopsis

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) */
};

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 only employ 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).

Conforming to

POSIX.1-2001.

Referenced By