root/deadlock.c

DEFINITIONS

1. main

#include<fcntl.h>
#include<unistd.h>
#include<errno.h>
typedef struct uinfo {
        char name[20];
        int accesscount;
} userinfo;

userinfo rec;


int main() {
        struct flock fl;
        int fd,r;

        fd=open("userdb.txt",O_RDWR);

        fl.l_type=F_WRLCK; 
        fl.l_whence=SEEK_SET; 
        fl.l_len=sizeof(userinfo);
        if (fork()) {
                fl.l_start=0;
                r=fcntl(fd,F_SETLK,&fl);
                if (r<0) {
                        perror("parent: lock 0");
                        return (-1);
                } 
                sleep(1);
                fl.l_start=sizeof(userinfo);
                r=fcntl(fd,F_SETLKW,&fl);
                if (r<0) {
                        perror("parent: lock 1");
                        return (-1);
                } 
        } else {
                fl.l_start=sizeof(userinfo);
                r=fcntl(fd,F_SETLK,&fl);
                if (r<0) {
                        perror("child: lock 1");
                        return (-1);
                } 
                sleep(1);
                fl.l_start=0;
                r=fcntl(fd,F_SETLKW,&fl);
                if (r<0) {
                        perror("child: lock 0");
                        return (-1);
                } 
        }

        return 0;
}