使用以下方法从串行端口读取数据时遇到问题，该方法由访问同一串行端口的两个线程组成。
虽然 tx 线程工作可靠，但始终有数据要发送，如果应用程序启动后不久数据不存在（RX/接收），则 rx 不起作用
两个线程具有相似的结构来使用“选择”来传输或接收数据。任何进一步调试的建议，为什么选择不能随着时间的推移接收数据。
void SerialEngine:: thread_rx()
{
struct timeval tv;
tv.tv_sec = 0;
tv.tv_usec = 0;
int count_tmp=0;
uint8_t read_serial_byte[1];
uint8_t data;
int serial_index = 0, rx_state = 0, gps_index = 0, hmi_index = 0 , GPS_HMI = 0;
uint8_t read_serial[2500]={0};
rfd = open(portname, O_RDWR | O_NOCTTY | O_SYNC | O_NDELAY | O_NONBLOCK);
if (rfd < 0) {
printf("Error opening read %s: %s\n", portname, strerror(errno));}
while(!signaled)
{
//printf("Recval1 is %d \n", recval1);
FD_ZERO(&readfds);
FD_SET(rfd, &readfds);
//printf("Xbee Rx trying again \n");
recval1 = select(rfd + 1, &readfds, NULL, NULL, &tv); //Reading Data from Xbee
if ((recval1 != -1) && (recval1 != 0))
{
if (FD_ISSET(rfd, &readfds))
{
int read_index = read(rfd, read_serial_byte,1);
//printf("Read Index is %d \n", read_index);
}
}
else if (recval1== -1)
{
}
else if (recval1 == 0)
{
}
}
}
void SerialEngine:: thread_serial_tx()
{
struct timeval tv;
tv.tv_sec = 5;
tv.tv_usec = 0;
wfd = open(portname, O_RDWR | O_NOCTTY | O_SYNC | O_NDELAY | O_NONBLOCK);
if (wfd < 0) {
printf("Error opening write %s: %s\n", portname, strerror(errno));}
Set_Serial_Atributes.set_interface_attribs(wfd, B115200);
FD_ZERO(&writefds);
FD_SET(wfd, &writefds);
recval2 = select(wfd + 1, NULL, &writefds, NULL, &tv); //Writing Data to Xbee
while(!signaled)
{
if ((recval2 != -1) && (recval2 != 0))
{
if((!tx_queue.empty()))
{
tx_string_check = tx_queue.front();
int tx_str_len = tx_string_check.size();
int bytes_written = write(wfd,hmi_serial_check, tx_str_len);
tx_queue.pop(); 486,2 57%
}
}
else if (recval1== -1)
{
}
else if (recval1 == 0)
{
}
}
}