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  asyn-
       chronous 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

       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  regis-
               tered  using the sigaction(2) SA_SIGINFO flag, then the follow-
               ing 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

               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),   getad-
       drinfo_a(3), lio_listio(3), mq_notify(3), aio(7), pthreads(7)

       This  page  is  part of release 4.04 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

GNU                               2015-08-08                       SIGEVENT(7)
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