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NAME

       struct 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 only employ 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), mq_notify(3), pthreads(7)

COLOPHON

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