sigevent

Structure that describes an event

Synopsis:

#include <sys/siginfo.h>

struct sigevent {
        int                             sigev_notify;
#if defined(__WATCOMC__) && !defined(NO_EXT_KEYS)
        union {
                int                     sigev_signo;
                int                     sigev_coid;
                int                     sigev_id;
                void                    (*sigev_notify_function)(union sigval);
        };
#else
        union {
                int                     __sigev_signo;
                int                     __sigev_coid;
                int                     __sigev_id;
                void                    (*__sigev_notify_function)(union sigval);
        }                               __sigev_un1;
# define sigev_signo                    __sigev_un1.__sigev_signo
# define sigev_coid                     __sigev_un1.__sigev_coid
# define sigev_id                       __sigev_un1.__sigev_id
# define sigev_notify_function          __sigev_un1.__sigev_notify_function
#endif
        union sigval    sigev_value;
#if defined(__WATCOMC__) && !defined(NO_EXT_KEYS)
        union {
                struct {
                        short           sigev_code;
                        short           sigev_priority;
                };
                pthread_attr_t  *sigev_notify_attributes;
        };
#else
        union {
                struct {
                        short           __sigev_code;
                        short           __sigev_priority;
                } __st;
                pthread_attr_t  *__sigev_notify_attributes;
        }                               __sigev_un2;
# define sigev_notify_attributes        __sigev_un2.__sigev_notify_attributes
# define sigev_code                     __sigev_un2.__st.__sigev_code
# define sigev_priority                 __sigev_un2.__st.__sigev_priority
#endif
};

Description:

This structure describes an event. POSIX specifies the basic structure and allows a lot of leeway in extending it. It effectively includes these members (although they aren't all usable at the same time):

The int sigev_notify member indicates how the notification is to occur, as well as which of the other members are used:

• SIGEV_INTR
• SIGEV_NONE
• SIGEV_PULSE
• SIGEV_SIGNAL
• SIGEV_SIGNAL_CODE
• SIGEV_SIGNAL_THREAD
• SIGEV_THREAD
• SIGEV_UNBLOCK

---

The library uses some of the extra bits in sigev_notify for other purposes (see “Critical threads,” below). After initializing an event, don't set sigev_notify directly; instead, use the SIGEV_SET_TYPE() macro. For example: SIGEV_SET_TYPE(&my_event, SIGEV_PULSE) If you want to test the value of this member, use the SIGEV_GET_TYPE() macro. For example, instead of: if( my_event.sigev_notify == SIGEV_PULSE) use: if( SIGEV_GET_TYPE(&my_event) == SIGEV_PULSE)

---

The <sys/siginfo.h> file also defines some macros to make initializing the sigevent structure easier. All the macros take a pointer to a sigevent structure as their event argument and set the sigev_notify member to the appropriate value. These macros are QNX Neutrino extensions and are described below.

SIGEV_INTR (QNX Neutrino extension)

Send an interrupt notification to a specific thread. No other fields in the structure are used.

The initialization macro is:

SIGEV_INTR_INIT( &event )

SIGEV_NONE (POSIX)

Don't send any notification. No other fields in the structure are used.

The initialization macro is:

SIGEV_NONE_INIT( &event )

SIGEV_PULSE (QNX Neutrino extension)

Send a pulse. The following fields are used:

int sigev_coid

The connection ID. This should be attached to the channel with which the pulse will be received.

short sigev_priority

The priority of the pulse, or SIGEV_PULSE_PRIO_INHERIT if you want the thread that receives the pulse to run at the initial priority of the process.

short sigev_code

A code to be interpreted by the pulse handler. Although sigev_code can be any 8-bit signed value, you should avoid sigev_code values less than zero in order to avoid conflict with kernel or pulse codes generated by a QNX Neutrino manager. These codes all start with _PULSE_CODE_ and are defined in <sys/neutrino.h>; for more information, see the documentation for the _pulse structure. A safe range of pulse values is _PULSE_CODE_MINAVAIL to _PULSE_CODE_MAXAVAIL.

int sigev_value.sival_int

A 32-bit value to be interpreted by the pulse handler.

The initialization macro is:

SIGEV_PULSE_INIT( &event, coid, priority, code, value )

SIGEV_SIGNAL (POSIX)

Send a signal to a process. The following fields are used:

int sigev_signo

The signal to raise. This must be in the range from 1 through NSIG − 1.

The initialization macro is:

SIGEV_SIGNAL_INIT( &event, signal )

If you need to set the sigev_value for a SIGEV_SIGNAL event (for example if SA_SIGINFO is set), you can use this macro:

SIGEV_SIGNAL_VALUE_INIT( &event, signal, value )

SIGEV_SIGNAL_CODE (QNX Neutrino extension)

This is similar to SIGEV_SIGNAL, except that SIGEV_SIGNAL_CODE also includes a value and a code. The following fields are used:

int sigev_signo

The signal to raise. This must be in the range from 1 through NSIG − 1.

short sigev_code

A code to be interpreted by the signal handler. This must be in the range from SI_MINAVAIL through SI_MAXAVAIL.

int sigev_value.sival_int

A 32-bit value to be interpreted by the signal handler.

The initialization macro is:

SIGEV_SIGNAL_CODE_INIT( &event, signal, value, code )

SIGEV_SIGNAL_THREAD (QNX Neutrino extension)

Send a signal to a specific thread, depending on the situation:

• If used with MsgSend*(), MsgReceive*(), and MsgDeliverEvent(), the thread is the one identified by the rcvid that MsgReceive*() returns.
• For timers, it's the thread that called timer_settime().
• For InterruptAttach() and InterruptAttachEvent(), it's the thread attaching to the interrupt.
• For asyncmsg_channel_create(), it's a random thread in the process.
• For SyncMutexEvent(), it's the thread that called the function.

In the case of timers, SyncMutexEvent(), and interrupts, if the thread dies before the event gets delivered, the kernel sends the signal to a random thread in the same process.

The following fields are used:

int sigev_signo

The signal to raise. This must be in the range from 1 through NSIG − 1.

short sigev_code

A code to be interpreted by the signal handler. This must be in the range from SI_MINAVAIL through SI_MAXAVAIL.

int sigev_value.sival_int

A 32-bit value to be interpreted by the signal handler.

The initialization macro is:

SIGEV_SIGNAL_THREAD_INIT( &event, signal, value, code )

SIGEV_THREAD (POSIX)

Create a new thread.

---

We don't recommend using this type of event. Pulses are more efficient.

---

The following fields are used:

void (*sigev_notify_function) (union sigval)

A pointer to the function to be notified.

pthread_attr *sigev_notify_attributes

A pointer to thread attributes. This must be NULL, or point to a structure initialized by pthread_attr_init() at the time of delivery.

void *sigev_value.sival_ptr

A value that's to be passed to the notification function.

The initialization macro is:

SIGEV_THREAD_INIT( &event, fn, value, attr )

The sigval union is defined as follows:

union sigval {
    int        sival_int;
    void     * sival_ptr;
};

SIGEV_UNBLOCK (QNX Neutrino extension)

Force a thread to become unblocked. No other fields in the structure are used.

The initialization macro is:

SIGEV_UNBLOCK_INIT( &event )

Critical threads (QNX Neutrino extension)

If you're using adaptive partitioning, you can use a sigevent to make a thread run as critical or not.

---

This feature was added in the QNX Neutrino Core OS 6.3.2. For more information, see the Adaptive Partitioning User's Guide.

---

After setting up the sigevent structure as appropriate, use these macros to set or clear the hidden bit that makes a thread run as critical or not:

SIGEV_MAKE_CRITICAL( &event )

Make the targeted thread run as critical.

SIGEV_CLEAR_CRITICAL( &event )

Make the targeted thread not run as critical.

The receiving thread doesn't have to do anything to make itself critical or noncritical; the adaptive partitioning scheduler does this automatically.

---

These macros use hidden bits in the sigev_notify member of the sigevent structure. Don't set or compare this member directly to a value; use the SIGEV_SET_TYPE() or SIGEV_GET_TYPE() macro instead, as described above.

---

Classification:

POSIX, with QNX Neutrino extensions

See also:

ds_create(), InterruptAttach(), InterruptAttachEvent(), iofunc_notify(), iofunc_notify_trigger(), ionotify(), lio_listio(), mq_notify(), MsgDeliverEvent(), procmgr_event_notify(), _pulse, SyncMutexEvent(), TimerCreate(), timer_create(), TimerInfo(), TimerTimeout(), timer_timeout()

Interprocess Communication (IPC) chapter of the System Architecture guide

Adaptive Partitioning User's Guide