SIGEVENT(7)               (2020-11-01)                SIGEVENT(7)

     NAME
          sigevent - structure for notification from asynchronous
          routines

     SYNOPSIS
          #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 */
          };

     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 employ only those fields rele-
          vant 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.

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     SIGEVENT(7)               (2020-11-01)                SIGEVENT(7)

               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).

     SEE ALSO
          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)

     COLOPHON
          This page is part of release 5.10 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 https://www.kernel.org/doc/man-pages/.

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