2003-01-10 05:34:11 +00:00
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.\" Copyright (c) 2003 Tim J. Robbins
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.\" All rights reserved.
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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 AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd January 10, 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 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 *stream"
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.Ft int
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.Fn ftrylockfile "FILE *stream"
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.Ft void
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.Fn funlockfile "FILE *stream"
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.Sh DESCRIPTION
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These functions provide explicit application-level locking of stdio streams.
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They can be used to avoid output from multiple threads being interspersed,
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2003-01-10 06:52:19 +00:00
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input being dispersed among multiple readers, and to avoid the overhead
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2003-01-10 05:34:11 +00:00
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of locking the stream for each operation.
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.Pp
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The
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.Fn flockfile
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function acquires an exclusive lock on the specified stream.
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If another thread has already locked the stream,
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.Fn flockfile
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will block until the lock is released.
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.Pp
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The
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.Fn ftrylockfile
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function is a non-blocking version of
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.Fn flockfile ;
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if the lock cannot be acquired immediately,
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.Fn ftrylockfile
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returns non-zero instead of blocking.
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.Pp
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The
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.Fn funlockfile
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function releases the lock on a stream acquired by an earlier call to
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.Fn flockfile
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or
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.Fn ftrylockfile .
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.Pp
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These functions behave as if there is a lock count associated
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with each stream.
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Each time
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.Fn flockfile
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is called on the stream, the count is incremented,
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and each time
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.Fn funlockfile
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is called on the stream, the count is decremented.
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The lock is only actually released when the count reaches zero.
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.Sh RETURN VALUES
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The
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.Fn flockfile
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and
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.Fn funlockfile
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functions return no value.
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.Pp
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The
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.Fn ftrylockfile
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2003-01-13 01:29:14 +00:00
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function
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2003-01-10 05:34:11 +00:00
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returns zero if the stream was successfully locked,
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non-zero otherwise.
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.Sh SEE ALSO
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.Xr getc_unlocked 3 ,
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.Xr putc_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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