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NetBSD 6.1.5 - man page for sigevent (netbsd section 3)

SIGEVENT(3)			   BSD Library Functions Manual 		      SIGEVENT(3)

NAME
     sigevent -- 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 currently 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 expira-
     tion occurs.  The possiblue values are:

       SIGEV_NONE     This constant specifies a ``null'' handler: when a notification 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 speci-
		      fied in sigev_signo.

		      In the signal handler the 'si_value' of siginfo_t is set to the value spec-
		      ified 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 specified 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 creates 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 unspecified 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 mem-
		      ory nor the address of the memory possibly dedicated as thread stack via
		      pthread_attr_setstack() or pthread_attr_setstackaddr().

SEE ALSO
     siginfo(2), timer_create(2), aio(3), mq(3)

HISTORY
     The sigevent structure first appeared in NetBSD 1.6.

BSD					  June 24, 2010 				      BSD


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