flock c/c++ Sample Code

flock() is to apply or remove an advisory lock on an open file. It is available on most of OS, and I have tried it and it can work on Linux and Android OS. It can resolve the problem which muti-processes access the same file.

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/file.h>
#include <iostream>

void lockUnLock() {
  int fd, i;
  char path[] = "test.txt";
  fd = open(path, O_WRONLY | O_CREAT);
  if (fd != -1) {
    std::cout << "open file " << path << std::endl;
    std::cout << "Please input a number to lock the file" << path << std::endl;
    scanf("%d", &i);
    if (flock(fd, 2) == 0) {
      std::cout << "The file was locked " << std::endl;
    } else {
      std::cout << "The file was not locked " << std::endl;
    }
    std::cout << "please input a number to unlock the file " << std::endl;
    scanf("%d", &i);
    if (flock(fd, 8) == 0) {
      std::cout << "The file was unlocked. " << std::endl;
    } else {
      std::cout << "The file was no unlocked. " << std::endl;
    }
    close(fd);
  } else {
    std::cout << "Cannot open file " << path << std::endl;
  }
}

int main() {
  lockUnLock();
  return 0;
}

Src code: : https://gist.github.com/tzutalin/ad4277e8ee24392b9ea23765452d6528
Note: You can also use semget/semop to do that, but Android Bionic does not support that..