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/*
Copyright (C) 2011 Laszlo Kajan, Technical University of Munich, Germany
This file is part of librostlab.
librostlab is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef ROSTLAB_FLOCK_RESOURCE
#define ROSTLAB_FLOCK_RESOURCE
#include <errno.h>
#include <fcntl.h>
#include <iostream>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include "rostlab/rostlab_stdexcept.h"
namespace rostlab {
/** File locking resource implemented with fcntl()/POSIX locking API
**
** fcntl()/POSIX locking also works with NFS.
*/
class file_lock_resource
{
private:
std::string _filename;
FILE* _fh;
// this is a resource - disable copy contructor and copy assignment
file_lock_resource( const file_lock_resource& ){};
file_lock_resource&
operator=(const file_lock_resource&){return *this;};
public:
bool dbg;
class wouldblock : public exception {};
public:
file_lock_resource() : _fh(NULL), dbg(false) {};
/** __mode: "r", "r+", "w", "w+", "a", "a+"; __cmd: F_SETLK, F_SETLKW; __type: F_RDLCK, F_WRLCK
*/
file_lock_resource( const std::string& __file, const std::string& __mode = "r", int __cmd = F_SETLKW, short __type = F_RDLCK, bool __dbg = false ) : _fh(NULL), dbg(__dbg)
{
acquire( __file, __mode, __cmd, __type, __dbg );
}
inline void acquire( const std::string& __file, const std::string& __mode = "r", int __cmd = F_SETLKW, short __type = F_RDLCK, bool __dbg = false ) throw ( runtime_error, wouldblock )
{
dbg = __dbg;
release();
//
_filename = __file;
_fh = fopen( _filename.c_str(), __mode.c_str() );
if( !_fh ) throw runtime_error( strerror( errno ) );
// instead of flock us fcntl()/POSIX locking so that it works with NFS as well
flock lock;
lock.l_type = __type;
lock.l_whence = SEEK_SET;
lock.l_start = 0;
lock.l_len = 0;
if( fcntl( fileno(_fh), __cmd, &lock ) )
{
int fcntl_errno = errno;
fclose(_fh); _fh = NULL;
if( fcntl_errno == EACCES || fcntl_errno == EAGAIN ) throw wouldblock();
else throw runtime_error( strerror( fcntl_errno ) );
}
else if(dbg) std::cerr << "LOCK_" << __mode << " " << __cmd << " " << __type << " '" << _filename << "'\n";
}
inline void release() throw (runtime_error)
{
if( _fh )
{
// lkajan: no need to explicitly release the lock: it is released when the file is closed
if( fclose(_fh) ) throw runtime_error( strerror( errno ) );
if(dbg) std::cerr << "LOCK_UN '" << _filename << "'\n";
_fh = NULL;
}
}
virtual ~file_lock_resource()
{
release();
}
operator FILE* () { return _fh; }
inline const std::string&
filename() const { return _filename; }
};
};
#endif // ROSTLAB_FLOCK_RESOURCE
// vim:et:ts=2:ai:
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