通过文件独占的方式,我们打开指定的文件后,用 lockf 对文件加锁,结束程序时解锁文件。
下面代码中我们将当前程序的 PID 写入文件。
int writePidFile(const char *pidFile) {
char str[32];
int fd = open(pidFile, O_WRONLY | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
if (fd < 0) {
printf("Can't open pidFile %s.
", pidFile);
exit(1);
}
// Lock pidFile.
if (lockf(fd, F_TLOCK, 0)) {
printf("Can't lock pidFile %s.
", pidFile);
exit(0);
}
sprintf(str, "%d
", getpid());
// Write pid to pidFile.
ssize_t len = strlen(str);
if (write(fd, str, len) != len) {
printf("Can't write pidFile %s.
", pidFile);
exit(0);
}
printf("Wrote pid file %s.
", pidFile);
return fd;
}
int main(){
int pid_fd = writePidFile("server.pid");
...
lockf(pid_fd, F_ULOCK, 0);
close(pid_fd);
}