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SIGEVENT

Linux Programmer's Manual (7)
2011-09-09
 

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 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).
 

CONFORMING TO

POSIX.1-2001.  

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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Index

NAME
SYNOPSIS
DESCRIPTION
CONFORMING TO
SEE ALSO
COLOPHON

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Time: 21:43:05 GMT, July 12, 2014