UART Interrupt problem while performing real-time image processing with camera by using opencv in c++ (I worked on Ubuntu 18.04, Linux Kernel 5x) - image-processing

Question

I write a code to process real time video by using camera. I can run this code within any error by itself but I want to implement a UART interrupt. Basically I aim that when I take a data from UART, other processes will be interrupted and after reading data, processes will be continue.
Here my UART interrupt implemented code.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <errno.h>
#include <termios.h>
#include <opencv2/opencv.hpp>
#include <iostream>
using namespace std;
using namespace cv;
void signal_handler_IO(int status);
VideoCapture vid("/dev/video0", CAP_V4L2);
int n;
int fd;
int connected;
struct termios termAttr;
struct sigaction saio;
const int fps = 20;
int main(int argc, char *argv[])
{
fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NDELAY);
Mat frame;
if (fd == -1)
{
perror("open_port: Unable to open /dev/ttyO1\n");
exit(1);
}
saio.sa_handler = signal_handler_IO;
saio.sa_flags = 0;
saio.sa_restorer = NULL; //
sigaction(SIGIO,&saio,NULL);
fcntl(fd, F_SETFL, FNDELAY|FASYNC);
fcntl(fd, F_SETOWN, getpid());
tcgetattr(fd,&termAttr);
cfsetispeed(&termAttr,B9600);
cfsetospeed(&termAttr,B9600);
termAttr.c_cflag &= ~PARENB; // --> Parity Enable
termAttr.c_cflag &= ~CSTOPB; // -->two stop bit else one
termAttr.c_cflag &= ~CSIZE; // Character Size (C5, C6...)
termAttr.c_cflag |= CS8; // Charachter size 8 bit
termAttr.c_cflag |= (CLOCAL | CREAD);
//CLOCAL --> Ignore modem status lines. ¦ CREAD --> Enable receiver.
termAttr.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
termAttr.c_iflag &= ~(IXON | IXOFF | IXANY);
termAttr.c_oflag &= ~OPOST; // OPOST --> Post-process output
tcsetattr(fd, TCSANOW, &termAttr);
printf("UART1 configured....\n");
connected = 1;
if (!vid.isOpened())
{
return -1;
}
vid.set(CAP_PROP_FRAME_WIDTH, 1280);
vid.set(CAP_PROP_FRAME_HEIGHT, 720);
while (vid.read(frame))
{
imshow("webcam", frame);
if (waitKey(1000/fps) >= 0)
break;
}
destroyAllWindows();
vid.release();
close(fd);
exit(0);
}
void signal_handler_IO (int status)
{
printf("received data from UART.\n");
}
Now let's get to the main problem:
When I implement UART interrupt to this code, my captured video was stopped by the core (I takes Core Dumped Error). I guess that after process interrupted and when it will continue again, compiler is try to set again the video properties which I defined as
(vid.set(CAP_PROP_FRAME_WIDTH, 1280);)
(vid.set(CAP_PROP_FRAME_HEIGHT, 720);)
so I think I got such an error.
I think as I mentioned because when I deleted these size setting commands, code run very well with UART interrupt.
I try to define these commands globally but I cant do this. I take "vid does not name a type." error.
Thus, I can't solve this problem. I am not sure about why this problem occur and I don't know how it will be solved.

Answer 1

First, you cannot invoke printf(3) in a signal handler. Printf interacts with stdio, which in turn interacts with malloc(3); neither of these frameworks are signal safe. So, change your printf() to a write(2), which is safe.
That is unlikely to be your problem.
You didn't post the source to the implementation of vid, and in particular, how does vid.read deal with signals (ie EINTR)? Does it handle them correctly? Well? Perhaps return 0 if it is interrupted?
You will likely need to vet vid., so you should have a test candidate that gets a timer based signal over random intervals to gain confidence that it works.