ptg10805159Appendix C Chapter 14 Solutions 931
exit(0);
}else { /* parent */
sleep(2);
}/*
*Parent continues ... read-lock the file again.
*/
if ((pid2 = fork()) < 0) {
err_sys("fork failed");
}else if (pid2 == 0) { /* child */
if (lock_reg(fd, F_SETLK, F_RDLCK, 0, SEEK_SET, 0) < 0)
err_sys("child 2: can’t read-lock file");
printf("child 2: obtained read lock on file\n");
pause();
printf("child 2: exit after pause\n");
exit(0);
}else { /* parent */
sleep(2);
}/*
*Parent continues ... block while trying to write-lock
*the file.
*/
if ((pid3 = fork()) < 0) {
err_sys("fork failed");
}else if (pid3 == 0) { /* child */
if (lock_reg(fd, F_SETLK, F_WRLCK, 0, SEEK_SET, 0) < 0)
printf("child 3: can’t set write lock: %s\n",
strerror(errno));
printf("child 3 about to block in write-lock...\n");
if (lock_reg(fd, F_SETLKW, F_WRLCK, 0, SEEK_SET, 0) < 0)
err_sys("child 3: can’t write-lock file");
printf("child 3 returned and got write lock????\n");
pause();
printf("child 3: exit after pause\n");
exit(0);
}else { /* parent */
sleep(2);
}/*
*See if a pending write lock will block the next
*read-lock attempt.
*/
if (lock_reg(fd, F_SETLK, F_RDLCK, 0, SEEK_SET, 0) < 0)
printf("parent: can’t set read lock: %s\n",
strerror(errno));
else
printf("parent: obtained additional read lock while"