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
  pid_t   sigev_notify_thread_id;
/* ID of thread to signal
(SIGEV_THREAD_ID); Linux-specific */


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:


A "null" notification: don't do anything when the event occurs.


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:


This field is set to a value that depends on the API delivering the notification.


This field is set to the signal number (i.e., the same value as in sigev_signo).


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).


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)


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  Copyright (C) 2006, 2010 Michael Kerrisk <>
Copyright (C) 2009 Petr Baudis <>

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