SIGEVENT(7)                                                             Linux Programmer's Manual                                                            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, expi‐
       ration 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 sig‐
              info_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  at‐
              tributes 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)

GNU                                                                            2021-03-22                                                                    SIGEVENT(7)