参考文章: http://blog.csdn.net/rl529014/article/details/51336161
http://blog.csdn.net/lin_fs/article/details/7804494
http://blog.csdn.net/querdaizhi/article/details/7478169
以flock函数打开设备文件打开,是独占整个文件
int fd;
char com_name[]={};
sprintf(com_name,"/dev/ttyS100%d",com_port);
// sprintf(com_name,"/dev/ttyS%d",1);
// printf("before first open\n");
fd = open(com_name, O_RDWR|O_NOCTTY|O_NDELAY);
// fd = open(com_name, O_RDWR|O_EXCL,0444);
if (fd < )
{
perror("open serial port");
return(-);
} if(flock(fd,LOCK_EX|LOCK_NB)==)
{
printf("the file was not locked.\n");
}
else
{
printf("the file was locked.\n");
close(fd);
return -;
} if (fcntl(fd, F_SETFL, ) < )
{
perror("fcntl F_SETFL\n");
} if (isatty(STDIN_FILENO) == )
{
perror("standard input is not a terminal device");
} return fd;
以fcntl方式打开设备文件:
int fd; char com_name[]={};
sprintf(com_name,"/dev/ttyS100%d",com_port);
// sprintf(com_name,"/dev/ttyS%d",1);
// printf("before first open\n");
fd = open(com_name, O_RDWR|O_NOCTTY|O_NDELAY);
// fd = open(com_name, O_RDWR|O_EXCL,0444);
if (fd < )
{
perror("open serial port");
return(-);
}
// printf("first open\n"); struct flock lock;
lock.l_type=F_WRLCK;
lock.l_pid=getpid();
lock.l_whence=SEEK_SET;
lock.l_start=;
lock.l_len=; fcntl(fd,F_GETLK,&lock); if(lock.l_type != F_UNLCK){
// printf("%d\n", lock.l_type);
return -;
} lock.l_type=F_WRLCK;
lock.l_pid=getpid();
lock.l_whence=SEEK_SET;
lock.l_start=;
lock.l_len=; if(fcntl(fd, F_SETLKW,&lock) < ){
perror("fcntl F_SETLKW\n");
} if (isatty(STDIN_FILENO) == )
{
perror("standard input is not a terminal device");
} return fd;
F_SETLKW 与 F_SETFL的区别是如果有其他锁阻止该锁被建立,则调用进程进入睡眠状态,等待该锁释放。一旦这个调用开始了等待,就只有在能够进行加锁或者收到信号时才会返回。
而且F_SETFL设置方式为fcntl(STDOUT_FILENO,F_SETFL,flags),而非fcntl(fd, F_SETLKW,&lock),无法建立锁机制。 F_SETFL 与 F_SETLKW 使用差别比较大