SIGEVENT(3) BSD Library Functions Manual SIGEVENT(3)NAMEsigevent — signal event structure
SYNOPSIS
#include <sys/signal.h>
DESCRIPTION
The IEEE Std 1003.1-2004 (“POSIX.1”) standard extends traditional UNIX
signal semantics by providing facilities for realtime signal generation
and delivery.
Please note that this manual describes an interface that is not yet fully
functional in NetBSD: neither realtime signals nor SIGEV_THREAD are cur‐
rently supported.
Realtime functions that can generate realtime signals include:
1. Completion of asynchronous I/O; see aio(3).
2. Expiration of per-process timers; see timer_create(2).
3. Arrival of a message to an empty message queue; see mq_notify(3).
The <sys/signal.h> header, included by <signal.h>, defines a sigevent
structure, which is the cornerstone in asynchronous delivery of realtime
signals. This structure is defined as:
struct sigevent {
int sigev_notify;
int sigev_signo;
union sigval sigev_value;
void (*sigev_notify_function)(union sigval);
void *sigev_notify_attributes;
};
The included union is further defined in <siginfo.h> as:
typedef union sigval {
int sival_int;
void *sival_ptr;
} sigval_t;
The sigev_notify integer defines the action taken when a notification
such as timer expiration occurs. The possiblue values are:
SIGEV_NONE This constant specifies a “null” handler: when a notifi‐
cation arrives, nothing happens.
SIGEV_SIGNAL The SIGEV_SIGNAL constant specifies that notifications
are delivered by signals. When a notification arrives,
the kernel sends the signal specified in sigev_signo.
In the signal handler the ‘si_value’ of siginfo_t is set
to the value specified by the sigev_value. In another
words, the sigev_value member is an application-defined
value to be passed to a particular signal handler at the
time of signal delivery. Depending whether the speci‐
fied value is an integer or a pointer, the delivered
value can be either sigval_intr or sigval_ptr.
SIGEV_THREAD This constant specifies a thread-driven notification
mechanism. When a notification occurs, the kernel cre‐
ates a new thread that starts executing the function
specified in the function pointer sigev_notify_function.
The single argument passed to the function is specified
in sigev_value.
If sigev_notify_attributes is not NULL, the provided
attribute specifies the behavior of the thread; see
pthread_attr(3). (Note that although a pointer to void
is specified for sigev_notify_attributes, the type is
pthread_attr_t in practice.)
The threads are created as detached, or in an unspeci‐
fied way if pthread_attr_setdetachstate(3) is used with
sigev_notify_attributes to set PTHREAD_CREATE_JOINABLE.
It is not valid to call pthread_join(3) in either case.
Hence, it is impossible to determine the lifetime of the
created thread. This in turn means that it is neither
possible to recover the memory nor the address of the
memory possibly dedicated as thread stack via
pthread_attr_setstack() or pthread_attr_setstackaddr().
SEE ALSOsiginfo(2), timer_create(2), aio(3), mq(3)HISTORY
The sigevent structure first appeared in NetBSD 1.6.
BSD June 24, 2010 BSD
