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       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 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:

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

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

               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

               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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