sigval(3type)

NAME#

sigevent, sigval - structure for notification from asynchronous routines

SYNOPSIS#

#include <signal.h>

struct sigevent {\n
\n    int             sigev_notify;\n  /* Notification type */
\n    int             sigev_signo;\n   /* Signal number */
\n    union sigval    sigev_value;\n   /* Data passed with notification */
\n    void          (*sigev_notify_function)(union sigval);\n
\n                                \n   /* Notification function
\n                                \n      (SIGEV_THREAD) */
\n    pthread_attr_t *sigev_notify_attributes;\n
\n                                \n   /* Notification attributes */
\n    \n/* Linux only: */
\n    pid_t           sigev_notify_thread_id;\n
\n                                \n   /* ID of thread to signal
\n                                \n      (SIGEV_THREAD_ID) */
\n};

union sigval {\n                     /* Data passed with notification */
\n    int             sival_int;\n     /* Integer value */
\n    void           *sival_ptr;\n     /* Pointer value */
\n};\n

DESCRIPTION#

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.

STANDARDS#

POSIX.1-2008.

HISTORY#

POSIX.1-2001.

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

NOTES#

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

SEE ALSO#

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