f14fb60209
* Updating common/lib * Updating lib/csu * Updating lib/libc * Updating libexec/ld.elf_so * Corrected test on __minix in featuretest to actually follow the meaning of the comment. * Cleaned up _REENTRANT-related defintions. * Disabled -D_REENTRANT for libfetch * Removing some unneeded __NBSD_LIBC defines and tests Change-Id: Ic1394baef74d11b9f86b312f5ff4bbc3cbf72ce2
128 lines
3.9 KiB
Groff
128 lines
3.9 KiB
Groff
.\" $NetBSD: flockfile.3,v 1.6 2011/10/15 21:43:19 wiz 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 October 15, 2011
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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 flock 2 ,
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.Xr getc_unlocked 3 ,
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.Xr getchar_unlocked 3 ,
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.Xr lockf 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 HISTORY
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The
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.Fn flockfile
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function first appeared in
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.Fx 2.0 .
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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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