sigevent - structure for notification from asynchronous routines


   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

   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

   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

           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

           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)


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at


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