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       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
                                    (SIGEV_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:

              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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