181 lines
4.9 KiB
Groff
181 lines
4.9 KiB
Groff
.\" $NetBSD: sigevent.3,v 1.8 2010/06/24 04:21:58 jruoho Exp $
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.\"
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.\" Copyright (c) 2010 Jukka Ruohonen <jruohonen@iki.fi>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd June 24, 2010
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.Dt SIGEVENT 3
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.Os
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.Sh NAME
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.Nm sigevent
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.Nd signal event structure
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.Sh SYNOPSIS
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.In sys/signal.h
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.Sh DESCRIPTION
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The
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.St -p1003.1-2004
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standard extends traditional
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.Tn UNIX
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signal semantics by providing facilities
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for realtime signal generation and delivery.
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.Pp
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.\"
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.\" XXX: Remove once these are fixed.
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.\"
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.Bf -symbolic
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Please note that this manual describes an interface that
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is not yet fully functional in
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.Nx :
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neither realtime signals nor SIGEV_THREAD
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are currently supported.
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.Ef
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.Pp
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Realtime functions that can generate realtime signals include:
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.Bl -enum -offset 3n
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.It
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Completion of asynchronous
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.Tn I/O ;
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see
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.Xr aio 3 .
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.It
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Expiration of per-process timers; see
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.Xr timer_create 2 .
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.It
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Arrival of a message to an empty message queue; see
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.Xr mq_notify 3 .
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.El
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.Pp
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The
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.In sys/signal.h
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header, included by
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.In signal.h ,
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defines a
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.Va sigevent
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structure, which is the cornerstone in
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asynchronous delivery of realtime signals.
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This structure is defined as:
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.Bd -literal -offset indent
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struct sigevent {
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int sigev_notify;
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int sigev_signo;
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union sigval sigev_value;
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void (*sigev_notify_function)(union sigval);
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void *sigev_notify_attributes;
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};
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.Ed
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.Pp
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The included union is further defined in
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.In siginfo.h
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as:
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.Bd -literal -offset indent
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typedef union sigval {
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int sival_int;
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void *sival_ptr;
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} sigval_t;
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.Ed
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.Pp
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The
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.Va sigev_notify
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integer defines the action taken when
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a notification such as timer expiration occurs.
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The possiblue values are:
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.Bl -tag -width "SIGEV_THREAD " -offset 2n
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.It Dv SIGEV_NONE
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This constant specifies a
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.Dq null
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handler: when a notification arrives, nothing happens.
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.It Dv SIGEV_SIGNAL
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The
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.Dv SIGEV_SIGNAL
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constant specifies that notifications are delivered by signals.
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When a notification arrives, the kernel sends the signal specified in
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.Va sigev_signo .
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.Pp
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In the signal handler the
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.Sq si_value
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of
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.Va siginfo_t
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is set to the value specified by the
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.Va sigev_value .
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In another words, the
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.Va sigev_value
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member is an application-defined value to be passed to
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a particular signal handler at the time of signal delivery.
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Depending whether the specified value is an integer or a pointer, the
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delivered value can be either
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.Va sigval_intr
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or
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.Va sigval_ptr .
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.It Dv SIGEV_THREAD
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This constant specifies a thread-driven notification mechanism.
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When a notification occurs, the kernel creates a new thread that starts
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executing the function specified in the function pointer
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.Va sigev_notify_function .
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The single argument passed to the function is specified in
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.Va sigev_value .
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.Pp
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If
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.Va sigev_notify_attributes
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is not
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.Dv NULL ,
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the provided attribute specifies the behavior of the thread; see
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.Xr pthread_attr 3 .
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(Note that although a pointer to void is specified for
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.Va sigev_notify_attributes ,
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the type is
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.Va pthread_attr_t
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in practice.)
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.Pp
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The threads are created as detached,
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or in an unspecified way if
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.Xr pthread_attr_setdetachstate 3
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is used with
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.Va sigev_notify_attributes
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to set
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.Dv PTHREAD_CREATE_JOINABLE .
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It is not valid to call
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.Xr pthread_join 3
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in either case.
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Hence, it is impossible to determine the lifetime of the created thread.
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This in turn means that it is neither possible to recover the memory nor
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the address of the memory possibly dedicated as thread stack via
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.Fn pthread_attr_setstack
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or
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.Fn pthread_attr_setstackaddr .
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.El
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.\"
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.\" .Sh EXAMPLES
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.\"
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.\" XXX: Add one.
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.\"
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.Sh SEE ALSO
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.Xr siginfo 2 ,
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.Xr timer_create 2 ,
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.Xr aio 3 ,
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.Xr mq 3
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.Sh HISTORY
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The
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.Va sigevent
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structure first appeared in
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.Nx 1.6 .
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