prt-get/src/lockfile.cpp

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////////////////////////////////////////////////////////////////////////
// FILE: lockfile.cpp
// AUTHOR: Johannes Winkelmann, jw@tks6.net
// COPYRIGHT: (c) 2002 by Johannes Winkelmann
// ---------------------------------------------------------------------
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
////////////////////////////////////////////////////////////////////////
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <cstdio>
#include "lockfile.h"
using namespace std;
string LockFile::LOCK_SUFFIX = ".lock";
string LockFile::WRITE_LOCK_STRING = "write_lock";
string LockFile::READ_LOCK_STRING = "read_lock";
string LockFile::READ_WRITE_LOCK_STRING = "read_write_lock";
/*!
\brief a file locking class
*/
LockFile::LockFile()
: m_readLock( false ),
m_writeLock( false )
{
}
bool LockFile::lockRead()
{
if ( m_readLock ) {
// we already lock it, so it's a good lock
return true;
}
if ( m_writeLock ) {
// can't lock for read and write separatedly
return false;
}
struct stat buf;
if ( stat( m_fileName.c_str(), &buf) == 0 ) {
FILE* fp = fopen( m_fileName.c_str(), "w" );
if ( fp ) {
// file did not exist, could be created
m_writeLock = true;
fprintf( fp, "%s", READ_LOCK_STRING.c_str() );
fclose( fp );
return true;
}
} else {
// file exists, but it could be a read lock
// TODO: allow locking, increment lock count
}
// couldn't lock
return false;
}
/*!
lock the file
\return true if we have a lock
*/
bool LockFile::lockWrite()
{
if ( m_writeLock ) {
// we already lock it, so it's a good lock
return true;
}
if ( m_readLock ) {
// can't lock for read and write separatedly
return false;
}
struct stat buf;
if ( stat( m_fileName.c_str(), &buf) == -1 ) {
// file can not be stat'ed
FILE* fp = fopen( m_fileName.c_str(), "w" );
if ( fp ) {
// file did not exist, could be created
m_writeLock = true;
fprintf( fp, "%s", WRITE_LOCK_STRING.c_str() );
fclose( fp );
return true;
}
}
// couldn't lock
return false;
}
bool LockFile::lockReadWrite()
{
if ( m_readWriteLock ) {
// we already lock it, so it's a good lock
return true;
}
if ( m_writeLock || m_readLock ) {
// can't lock for read and write separatedly
return false;
}
struct stat buf;
if ( stat( m_fileName.c_str(), &buf) == 0 ) {
FILE* fp = fopen( m_fileName.c_str(), "w" );
if ( fp ) {
// file did not exist, could be created
m_writeLock = true;
fprintf( fp, "%s", READ_WRITE_LOCK_STRING.c_str() );
fclose( fp );
return true;
}
}
// couldn't lock
return false;
}
bool LockFile::unlock()
{
if ( m_readLock || m_writeLock || m_readWriteLock ) {
// TODO: check whether lock count is 0
if ( unlink( m_fileName.c_str() ) == 0 ) {
m_readLock = m_writeLock = m_readWriteLock = false;
return true;
}
}
return false;
}
void LockFile::setFile( const string& fileName )
{
m_fileName = fileName + LOCK_SUFFIX;
}