93 lines
2.3 KiB
C++
93 lines
2.3 KiB
C++
// include/atomic_ofstream.hh
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// This file is part of libpbe; see http://svn.chezphil.org/libpbe/
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// (C) 2008 Philip Endecott
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// This program is free software; you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 2 of the License, or
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// any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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#ifndef libpbe_atomic_ofstream_hh
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#define libpbe_atomic_ofstream_hh
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#include "Exception.hh"
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#include <unistd.h>
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#include <stdio.h>
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#include <fstream>
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#include <string>
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namespace pbe {
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// atomic_ofstream is like std::ofstream except that the stream writes to
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// a temporary file. When the file has been completely written the client
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// code should call commit() which removes any existing file and moves the
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// new one into its place; this should happen somewhat atomically. If
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// commit() has not been called by the time the destructor is reached
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// the temporary file is removed and the original file is left unchanged.
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struct atomic_ofstream_base {
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const std::string orig_fn;
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const std::string tmp_fn;
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atomic_ofstream_base(std::string orig_fn_):
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orig_fn(orig_fn_),
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tmp_fn(orig_fn+".tmp")
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{}
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};
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class atomic_ofstream:
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private atomic_ofstream_base,
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public std::ofstream {
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bool committed;
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public:
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atomic_ofstream(std::string orig_fn_):
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atomic_ofstream_base(orig_fn_),
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std::ofstream(tmp_fn.c_str()),
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committed(false)
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{}
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void commit() {
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if (!committed) {
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std::ofstream::close();
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// We don't need to remove the old file; rename() does this.
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int r = ::rename(tmp_fn.c_str(),orig_fn.c_str());
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if (r==-1) {
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throw_ErrnoException("rename()");
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}
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committed = true;
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}
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}
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~atomic_ofstream() {
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if (!committed) {
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std::ofstream::close();
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::unlink(tmp_fn.c_str());
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}
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}
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};
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};
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#endif
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