2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
120 lines
3.8 KiB
Groff
120 lines
3.8 KiB
Groff
.\" $NetBSD: flockfile.3,v 1.4 2008/04/30 13:10:51 martin Exp $
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.\"
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.\" Copyright (c) 2003 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 Klaus Klein.
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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 January 28, 2003
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.Dt FLOCKFILE 3
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.Os
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.Sh NAME
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.Nm flockfile ,
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.Nm ftrylockfile ,
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.Nm funlockfile
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.Nd stdio stream locking functions
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdio.h
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.Ft void
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.Fn flockfile "FILE *file"
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.Ft int
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.Fn ftrylockfile "FILE *file"
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.Ft void
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.Fn funlockfile "FILE *file"
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.Sh DESCRIPTION
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The
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.Fn flockfile ,
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.Fn ftrylockfile ,
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and
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.Fn funlockfile
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functions provide applications with explicit control of locking of
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stdio stream objects.
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They can be used by a thread to execute a sequence of I/O operations
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as a unit, without interference from another thread.
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.Pp
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Locks on stdio streams are recursive, and a lock count is maintained.
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stdio streams are created unlocked, with a lock count of zero.
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After successful acquisition of the lock, its count is incremented
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to one, indicating locked state of the stdio stream.
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Each subsequent relock operation performed by the owner thread
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increments the lock count by one, and each subsequent unlock
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operation performed by the owner thread decrements the lock count by one,
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allowing matching lock and unlock operations to be nested.
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After its lock count is decremented to zero, the stdio stream returns
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to unlocked state, and ownership of the stdio stream is relinquished.
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.Pp
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The
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.Fn flockfile
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function acquires the ownership of
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.Fa file
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for the calling thread.
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If
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.Fa file
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is already owned by another thread, the calling thread is suspended
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until the acquisition is possible (i.e.,
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.Fa file
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is relinquished again and the calling thread is scheduled to acquire it).
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.Pp
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The
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.Fn ftrylockfile
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function acquires the ownership of
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.Fa file
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for the calling thread only if
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.Fa file
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is available.
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.Pp
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The
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.Fn funlockfile
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function relinquishes the ownership of
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.Fa file
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previously granted to the calling thread.
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Only the current owner of
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.Fa file
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may
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.Fn funlockfile
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it.
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.Sh RETURN VALUES
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If successful, the
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.Fn ftrylockfile
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function returns 0.
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Otherwise, it returns non-zero to indicate that the lock cannot be acquired.
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.Sh SEE ALSO
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.Xr getc_unlocked 3 ,
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.Xr getchar_unlocked 3 ,
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.Xr putc_unlocked 3 ,
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.Xr putchar_unlocked 3
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.Sh STANDARDS
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The
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.Fn flockfile ,
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.Fn ftrylockfile
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and
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.Fn funlockfile
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functions conform to
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.St -p1003.1-2001 .
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.Sh BUGS
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The design of these interfaces does not allow for addressing the
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problem of priority inversion.
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