file_lock.h

#ifndef FILE_LOCK_H_INCLUDE_
#define FILE_LOCK_H_INCLUDE_

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

class FileLock {
    public:

        explicit FileLock(int file_des) {
            m_file_des = file_des;
        }

        FileLock() {
            m_file_des = -1;
        }

        void attach(int fd) {
            m_file_des = fd;
        }

        bool open(char const *file_name) {
            if(m_file_des >=0) {
                ::close(m_file_des);
            }

            m_file_des = ::open(file_name, O_CREAT|O_RDWR, 0664);
            return m_file_des >=0;
        }

        bool lock() {
            return lock_reg(m_file_des, F_SETLKW, F_WRLCK, 0, SEEK_SET, 0) >= 0;

        }

        bool try_lock(){
            return lock_reg(m_file_des, F_SETLK, F_WRLCK, 0, SEEK_SET, 0) >= 0;
        }

        bool unlock() {
            return lock_reg(m_file_des, F_SETLK, F_UNLCK, 0, SEEK_SET, 0) >= 0;
        }

        bool close() {
            if (m_file_des >=0) ::close(m_file_des);
            m_file_des = -1;
        return true;
        }

        ~FileLock() {
        }

        int m_file_des;
    private:
        FileLock(FileLock const &);
        FileLock & operator=(FileLock const &);

        int lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len) {
            if(fd < 0) {
                return -1;
            }

            struct flock lock;
            lock.l_type = type;
            lock.l_start = offset;
            lock.l_whence = whence;
            lock.l_len = len;
            return fcntl(fd, cmd, &lock);
        }
};

#endif //FILE_LOCK_H_INCLUDE_