173 lines
4.8 KiB
Groff
173 lines
4.8 KiB
Groff
.\" $NetBSD: _lwp_park.2,v 1.13 2022/12/04 16:17:50 uwe Exp $
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.\"
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.\" Copyright (c) 2003, 2007, 2017 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jason R. Thorpe of Wasabi Systems, Inc, and by Andrew Doran.
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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 July 30, 2019
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.Dt _LWP_PARK 2
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.Os
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.Sh NAME
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.Nm _lwp_park
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.Nd wait interruptably in the kernel
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In lwp.h
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.Ft int
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.Fn _lwp_park "clockid_t clock_id" "int flags" "struct timespec *ts" "lwpid_t unpark" "const void *hint" "const void *unparkhint"
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.Sh DESCRIPTION
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.Fn _lwp_park
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can be used to synchronize access to resources among multiple light-weight
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processes.
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It causes the calling LWP to wait interruptably in the kernel, until one
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of the following conditions is met:
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.Bl -bullet
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.It
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The
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.Fa ts
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argument is
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.Pf non- Dv NULL ,
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and the time it specifies has passed.
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The
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.Fa ts
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time can be a relative interval to wait if the
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.Fa flags
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argument does not contain
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.Dv TIMER_ABSTIME
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or it can be an absolute time.
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The
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.Fa clock_id
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argument contains the clock to be used; it can be:
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.Dv CLOCK_REALTIME
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or
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.Dv CLOCK_MONOTONIC .
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.It
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The LWP receives a directed signal posted using
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.Fn _lwp_kill ,
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or is elected to handle a signal on behalf of its containing process.
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.It
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The LWP is awoken by another LWP in the same process that has made
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a call to
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.Fn _lwp_wakeup .
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.It
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The LWP is awoken by another LWP in the same process that has made
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a call to
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.Fn _lwp_unpark
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or
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.Fn _lwp_unpark_all .
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.El
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.Pp
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If the
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.Fa ts
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argument contains a relative time interval, it will be modified to contain
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the remaining time to sleep when
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.Fn _lwp_park
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returns.
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.Pp
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The preferred method to awaken an LWP sleeping as a result of a call
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to
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.Fn _lwp_park
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is to make a call to
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.Fn _lwp_unpark ,
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or
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.Fn _lwp_unpark_all .
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The
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.Fn _lwp_wakeup
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system call is a more general facility, and requires more resources
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to execute.
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.Pp
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The optional
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.Fa hint
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argument specifies the address of an object upon which the LWP is
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synchronizing.
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When the
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.Fa hint
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value is matched between calls to
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.Fn _lwp_park
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and
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.Fn _lwp_unpark
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or
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.Fn _lwp_unpark_all ,
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it may reduce the time necessary for the system to resume execution
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of waiting LWPs.
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.Pp
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The
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.Fa unpark
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and
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.Fa unparkhint
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arguments can be used to fold a park operation and unpark operation into a
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single system call.
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If
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.Fa unpark
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is non-zero, the system will behave as if the following call had been made
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before the calling thread begins to wait:
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.Pp
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.Dl _lwp_unpark(unpark, unparkhint);
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.Sh RETURN VALUES
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.\" Rv -std _lwp_park
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.\" The "if successful" language in .Rv -std is misleading, but try to
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\" follow its phrasing as close as possible.
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The
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.Fn _lwp_park
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.\" XXX: TODO: when? be more precise
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function may return the value of 0.
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Otherwise the value \-1 is returned and the global variable
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.Va errno
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is set to provide more information.
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.Sh ERRORS
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.Bl -tag -width Er
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.It Bq Er EALREADY
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A request was made to wake the LWP before it began to wait in
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the kernel.
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.It Bq Er EINTR
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The LWP has been awoken by a signal or by a call to one of the
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following functions:
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.Fn _lwp_unpark ,
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.Fn _lwp_unpark_all ,
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.Fn _lwp_wakeup .
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.It Bq Er EINVAL
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The time value specified by
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.Fa ts
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is invalid.
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.It Bq Er ESRCH
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No LWP can be found in the current process corresponding to
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.Fa unpark .
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.It Bq Er ETIMEDOUT
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The UTC time specified by
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.Fa ts
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has passed.
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.El
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.Sh SEE ALSO
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.Xr _lwp_unpark 2 ,
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.Xr _lwp_unpark_all 2 ,
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.Xr _lwp_wakeup 2
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.Sh HISTORY
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The
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.Fn _lwp_park
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system call first appeared in
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.Nx 5.0 .
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