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Dd June 24, 2010
Dt SIGEVENT 3
Os
Sh NAME
Nm sigevent
Nd signal event structure
Sh SYNOPSIS
In sys/signal.h
Sh DESCRIPTION
The
St -p1003.1-2004
standard extends traditional
Tn UNIX
signal semantics by providing facilities
for realtime signal generation and delivery.
Pp
\"
\" XXX: Remove once these are fixed.
\"
Bf -symbolic
Please note that this manual describes an interface that
is not yet fully functional in
Nx :
neither realtime signals nor SIGEV_THREAD
are currently supported.
Ef
Pp
Realtime functions that can generate realtime signals include:
Bl -enum -offset 3n
It
Completion of asynchronous
Tn I/O ;
see
Xr aio 3 .
It
Expiration of per-process timers; see
Xr timer_create 2 .
It
Arrival of a message to an empty message queue; see
Xr mq_notify 3 .
El
Pp
The
In sys/signal.h
header, included by
In signal.h ,
defines a
Va sigevent
structure, which is the cornerstone in
asynchronous delivery of realtime signals.
This structure is defined as:
Bd -literal -offset indent
struct sigevent {
       int               sigev_notify;
       int               sigev_signo;
       union sigval      sigev_value;
       void            (*sigev_notify_function)(union sigval);
       void             *sigev_notify_attributes;
};
Ed
Pp
The included union is further defined in
In siginfo.h
as:
Bd -literal -offset indent
typedef union sigval {
       int      sival_int;
       void    *sival_ptr;
} sigval_t;
Ed
Pp
The
Va sigev_notify
integer defines the action taken when
a notification such as timer expiration occurs.
The possiblue values are:
Bl -tag -width "SIGEV_THREAD " -offset 2n
It Dv SIGEV_NONE
This constant specifies a
Dq null
handler: when a notification arrives, nothing happens.
It Dv SIGEV_SIGNAL
The
Dv SIGEV_SIGNAL
constant specifies that notifications are delivered by signals.
When a notification arrives, the kernel sends the signal specified in
Va sigev_signo .
Pp
In the signal handler the
Sq si_value
of
Va siginfo_t
is set to the value specified by the
Va sigev_value .
In another words, the
Va 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
Va sigval_intr
or
Va sigval_ptr .
It Dv 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
Va sigev_notify_function .
The single argument passed to the function is specified in
Va sigev_value .
Pp
If
Va sigev_notify_attributes
is not
Dv NULL ,
the provided attribute specifies the behavior of the thread; see
Xr pthread_attr 3 .
(Note that although a pointer to void is specified for
Va sigev_notify_attributes ,
the type is
Va pthread_attr_t
in practice.)
Pp
The threads are created as detached,
or in an unspecified way if
Xr pthread_attr_setdetachstate 3
is used with
Va sigev_notify_attributes
to set
Dv PTHREAD_CREATE_JOINABLE .
It is not valid to call
Xr 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
Fn pthread_attr_setstack
or
Fn pthread_attr_setstackaddr .
El
\"
\" .Sh EXAMPLES
\"
\" XXX: Add one.
\"
Sh SEE ALSO
Xr siginfo 2 ,
Xr timer_create 2 ,
Xr aio 3 ,
Xr mq 3
Sh HISTORY
The
Va sigevent
structure first appeared in
Nx 1.6 .

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