source: testjes/testdirlock.cpp

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

int main()
{
  int f;
  f = open(".",O_RDWR);
  if (f < 0)
  {
    perror("open error:");
    return 1;
  }
  int rc;
  struct flock lock;
  lock.l_type = F_RDLCK|F_WRLCK;
  lock.l_whence = SEEK_SET;
  lock.l_start  = 0;
  lock.l_len    = 0;

  std::cout << "getting lock ... \n";
  rc = fcntl(f,F_SETLKW,&lock);

  std::cout << " got it, sleeping\n";
  sleep(5);
  lock.l_type = F_UNLCK;
  lock.l_whence = SEEK_SET;
  lock.l_start  = 0;
  lock.l_len    = 0;
  rc  = fcntl(f,F_SETLKW,&lock);

  sleep(5);
  std::cout << "done\n";

  return 0;
}