* 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
127 lines
3.9 KiB
Groff
127 lines
3.9 KiB
Groff
.\" $NetBSD: flockfile.3,v 1.6 2011/10/15 21:43:19 wiz Exp $
|
|
.\"
|
|
.\" Copyright (c) 2003 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Klaus Klein.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
|
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
|
|
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
|
|
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
|
|
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
|
|
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
|
|
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
|
|
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
|
|
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
|
|
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
|
|
.\" POSSIBILITY OF SUCH DAMAGE.
|
|
.\"
|
|
.Dd October 15, 2011
|
|
.Dt FLOCKFILE 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm flockfile ,
|
|
.Nm ftrylockfile ,
|
|
.Nm funlockfile
|
|
.Nd stdio stream locking functions
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In stdio.h
|
|
.Ft void
|
|
.Fn flockfile "FILE *file"
|
|
.Ft int
|
|
.Fn ftrylockfile "FILE *file"
|
|
.Ft void
|
|
.Fn funlockfile "FILE *file"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Fn flockfile ,
|
|
.Fn ftrylockfile ,
|
|
and
|
|
.Fn funlockfile
|
|
functions provide applications with explicit control of locking of
|
|
stdio stream objects.
|
|
They can be used by a thread to execute a sequence of I/O operations
|
|
as a unit, without interference from another thread.
|
|
.Pp
|
|
Locks on stdio streams are recursive, and a lock count is maintained.
|
|
stdio streams are created unlocked, with a lock count of zero.
|
|
After successful acquisition of the lock, its count is incremented
|
|
to one, indicating locked state of the stdio stream.
|
|
Each subsequent relock operation performed by the owner thread
|
|
increments the lock count by one, and each subsequent unlock
|
|
operation performed by the owner thread decrements the lock count by one,
|
|
allowing matching lock and unlock operations to be nested.
|
|
After its lock count is decremented to zero, the stdio stream returns
|
|
to unlocked state, and ownership of the stdio stream is relinquished.
|
|
.Pp
|
|
The
|
|
.Fn flockfile
|
|
function acquires the ownership of
|
|
.Fa file
|
|
for the calling thread.
|
|
If
|
|
.Fa file
|
|
is already owned by another thread, the calling thread is suspended
|
|
until the acquisition is possible (i.e.,
|
|
.Fa file
|
|
is relinquished again and the calling thread is scheduled to acquire it).
|
|
.Pp
|
|
The
|
|
.Fn ftrylockfile
|
|
function acquires the ownership of
|
|
.Fa file
|
|
for the calling thread only if
|
|
.Fa file
|
|
is available.
|
|
.Pp
|
|
The
|
|
.Fn funlockfile
|
|
function relinquishes the ownership of
|
|
.Fa file
|
|
previously granted to the calling thread.
|
|
Only the current owner of
|
|
.Fa file
|
|
may
|
|
.Fn funlockfile
|
|
it.
|
|
.Sh RETURN VALUES
|
|
If successful, the
|
|
.Fn ftrylockfile
|
|
function returns 0.
|
|
Otherwise, it returns non-zero to indicate that the lock cannot be acquired.
|
|
.Sh SEE ALSO
|
|
.Xr flock 2 ,
|
|
.Xr getc_unlocked 3 ,
|
|
.Xr getchar_unlocked 3 ,
|
|
.Xr lockf 3 ,
|
|
.Xr putc_unlocked 3 ,
|
|
.Xr putchar_unlocked 3
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn flockfile ,
|
|
.Fn ftrylockfile
|
|
and
|
|
.Fn funlockfile
|
|
functions conform to
|
|
.St -p1003.1-2001 .
|
|
.Sh HISTORY
|
|
The
|
|
.Fn flockfile
|
|
function first appeared in
|
|
.Fx 2.0 .
|
|
.Sh BUGS
|
|
The design of these interfaces does not allow for addressing the
|
|
problem of priority inversion.
|