Share opencv image data in Linux

client.cc

#include "opencv2/opencv.hpp"

// For IPC
#include <sys/ipc.h>
#include <sys/shm.h>

#include <string.h>

using namespace std;
using namespace cv;

// 640*480 RGB image
const int buf_sz = 640*480*3;

key_t shmid;
int key = 3345678;
char *shm = NULL;
void init_shm() {

  if((shmid = shmget(key, buf_sz + 1, IPC_CREAT | 0666 )) < 0 ) {
    cout << "shmget failed" << endl;
    exit(1);
  }
  if((shm = (char*)shmat(shmid, NULL, 0) ) == (char *)-1) {
    cout << "shmat failed" << endl;
    exit(1);
  }
}

int main(int, char**)
{

    init_shm();
    for(;;)
    {
        Mat frame(480, 640, CV_8UC3);
        if(*shm == 1) {
          memcpy(frame.data, shm + 1, buf_sz);
          imshow("frame", frame);
          if(waitKey(30) >= 0) break;
          *shm = 0;
        }
    }
    // the camera will be deinitialized automatically in VideoCapture destructor
    return 0;
}
                       

Makefile

all:
	g++ server.cc -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_videoio -o server
	g++ client.cc -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_videoio -o client

server.cc

#include "opencv2/opencv.hpp"

// For IPC
#include <sys/ipc.h>
#include <sys/shm.h>
#include <string.h>

using namespace std;
using namespace cv;

// 640*480 RGB image
const int buf_sz = 640*480*3;

key_t shmid;
int key = 3345678;
char *shm = NULL;
void init_shm() {

  if((shmid = shmget(key, buf_sz + 1, IPC_CREAT | 0666 )) < 0 ) {
    cout << "shmget failed" << endl;
    exit(1);
  }

  if((shm = (char*)shmat(shmid, NULL, 0) ) == (char *)-1) {
    cout << "shmat failed" << endl;
    exit(1);
  }
}

int main(int, char**)
{

    VideoCapture cap(0); // open the default camera
    if(!cap.isOpened())  // check if we succeeded
        return -1;

    cout << "width=" << cap.get(CAP_PROP_FRAME_WIDTH) <<
            ", height=" << cap.get(CAP_PROP_FRAME_HEIGHT) << endl;

    init_shm();
    // Initialize buffer
    // Buffer = [header][data]
    memset(shm, 0, buf_sz + 1);


    // *shm == 0, accept
    // *shm == 1, pending    
    for(;;)
    {
        Mat frame;
        cap >> frame;
        if(*shm == 0) {
          memcpy(shm + 1, frame.data, buf_sz);
          *shm = 1;
        }
    }

    return 0;
}