#include <iostream>
#include <fcntl.h>
#include <unistd.h>

using std::cout;

int lock(const char * name) {
  char * namedotlck = new char[strlen(name)+4];
  strcpy(namedotlck, name);
  strcpy(namedotlck+strlen(name), ".lck");
  int status=link(name, namedotlck);
  delete[] namedotlck;
  return status+1;
}
 
int unlock(const char * name) {
  char * namedotlck = new char[strlen(name)+4];
  strcpy(namedotlck, name);
  strcpy(namedotlck+strlen(name), ".lck");
  int status=unlink(namedotlck);
  delete[] namedotlck;
  return status+1;
}

int main() {
  while (true) {
    //wait to obtain a lock
    while (!lock("somefile")); 
    int fd=open("somefile", O_WRONLY | O_APPEND);
    write(fd, "hello", 6);
    write(fd, "bye", 4);
    close(fd);
    //release lock
    unlock("somefile");
  }
}