sigevent, sigval - structure for notification from asynchronous routines

sigevent
       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:

       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).

   sigval
       Data passed with a signal.

       POSIX.1-2001.

       <aio.h> and <time.h> define sigevent since POSIX.1-2008.

       sigevent, sigval - structure for notification from asynchronous routines

       The following headers also provide sigevent: <aio.h>, <mqueue.h>, and <time.h>.

timer_create(2),  getaddrinfo_a(3),  lio_listio(3),   mq_notify(3),   pthread_sigqueue(3),   sigqueue(3),
       aiocb(3type), siginfo_t(3type)

Linux man-pages 6.9.1                              2024-05-02                                    sigevent(3type)

       POSIX.1-2008.

#include<signal.h>structsigevent{intsigev_notify;  /* Notification type */
           intsigev_signo;   /* Signal number */
           unionsigvalsigev_value;   /* Data passed with notification */

           void(*sigev_notify_function)(unionsigval);
                                          /* Notification function
                                             (SIGEV_THREAD) */
           pthread_attr_t*sigev_notify_attributes;
                                          /* Notification attributes */

           /* Linux only: */
           pid_tsigev_notify_thread_id;
                                          /* ID of thread to signal
                                             (SIGEV_THREAD_ID) */
       };unionsigval{                     /* Data passed with notification */
           intsival_int;     /* Integer value */
           void*sival_ptr;     /* Pointer value */
       };