APUE.zip_apue

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> int lock_reg(int fd, int cmd, int type, off_t offset, int whence, off_t len) { struct flock lock; lock.l_type = type; lock.l_start = offset; lock.l_whence = whence; lock.l_len = len; return (fcntl(fd, cmd, &flock)); } pid_t lock_test(int fd, int type, off_t offset, int whence, off_t len) { struct flock lock; lock.l_type = type; lock.l_start = offset; lock.l_whence = whence; lock.l_len = len; if (fcntl(fd, F_GETLK, &lock) < 0) { printf("fcntl error\n"); return -1; } if (lock.l_type == F_UNLCK) return 0; else return lock.l_pid; } #define read_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLK, F_RDLCK, (offset), (whence), (len)) #define readw_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLKW, F_RDLCK, (offset), (whence), (len)) #define write_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLK, F_WRLCK, (offset), (whence), (len)) #define writew_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLKW, F_WRLCK, (offset), (whence), (len)) #define un_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLK, F_UNLCK, (offset), (whence), (len)) #define is_read_lockable(fd, offset, whence, len) \ (lock_test((fd), F_RDLCK, (offset), (whence), (len)) == 0) #define is_write_lockable(fd, offset, whence, len) \ (lock_test((fd), F_WRLCK, (offset), (whence), (len)) == 0) void lockabyte(const char* name, int fd, off_t offset) { if (writew_lock(fd, offset, SEEK_SET, 1) < 0) { printf("lock error, %s\n", strerror(errno)); return; } printf("%s: get lock at byte %ld\n", name, offset); } int main() { int fd; pid_t pid; fd = creat("templock", S_IWUSR|S_IRUSR|S_IWGRP|S_IRGRP|S_IWOTH|S_IROTH); write(fd, "ab", 2); if ((pid=fork()) < 0) { printf("fork error\n"); return -1; } else if (pid > 0) { lockabyte("main", fd, 1); sleep(2); lockabyte("main", fd, 0); } else { lockabyte("chld", fd, 0); sleep(2); lockabyte("chld", fd, 1); } }