Can we use pthread library for opencv C++ programming? - c++

Question

I have implemented a openCV program which can capture frames from video file and process it and create a new file. That is doing for single in file . Now I want for multiple files . then I have an idea about POSIX thread pthread library . Is that is a good or bad idea . Actually when I implement pthreads in opencv program I got some errors like following :
OpenCV Error: Assertion failed (_src.sameSize(_dst) && dcn == scn) in
accumulate, file
/home/satinder/opencv_installation/OpenCV/opencv/modules/imgproc/src/accum.cpp,
line 915
what():
/home/satinder/opencv_installation/OpenCV/opencv/modules/imgproc/src/accum.cpp:915:
error: (-215) _src.sameSize(_dst) && dcn == scn in function accumulate
Aborted (core dumped)
corrupted double-linked list: 0x00007fcd048f73d0 ***
Aborted (core dumped)
seg fault also some time .
Is there any possible way how I can implement multi-threading or equivalent my goal make a program which can get more that one input files for same processing.
FOllowing is my code snapshot :
#include "opencv2/highgui/highgui.hpp"
#include <sys/types.h>
#include <pthread.h>
#include <iostream>
using namespace cv;
using namespace std;
void * VideoCap(void *);
void * VideoCap(void *arg)
{
VideoCapture cap((char *)arg); // open the video file for reading
if ( !cap.isOpened() ) // if not success, exit program
{
cout << "Cannot open the video file" << endl;
exit(1);
}
//cap.set(CV_CAP_PROP_POS_MSEC, 300); //start the video at 300ms
double fps = cap.get(CV_CAP_PROP_FPS); //get the frames per seconds of the video
cout << "Frame per seconds : " << fps << endl;
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
while(1)
{
Mat frame;
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "Cannot read the frame from video file" << endl;
break;
}
imshow("MyVideo", frame); //show the frame in "MyVideo" window
if(waitKey(30) == 27) //wait for 'esc' key press for 30 ms. If 'esc' key is pressed, break loop
{
cout << "esc key is pressed by user" << endl;
break;
}
}
}
int main(int argc, char* argv[])
{
int ret ;
pthread_t th[2];
ret = pthread_create(&th[0] , NULL , VideoCap , (void *)"cctv3.mp4");
if(0 == ret)
{
cout << "Thread 1 is created successfull" << endl;
}
ret = pthread_create(&th[1] , NULL , VideoCap , (void *)"cctv10.mp4");
if(0 == ret)
{
cout << "Thread 2 is created successfull" << endl;
}
pthread_join(th[0] , NULL);
pthread_join(th[1] , NULL);
return 0;
}

Answer 1

There are some problems with your code
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
You are creating two threads, so the windows should have different identifiers.
namedWindow((char *)arg, CV_WINDOW_AUTOSIZE);
...
imshow((char *)arg, frame);
Since this question was posted with linux tag, I'm guessing that gtk is relevant. After inserting the directives
#include <gdk/gdk.h>
#include <gtk/gtkmain.h>
at the beginning of the file and then in the main()
pthread_t th[2];
gtk_disable_setlocale();
gtk_init(&argc, &argv);
gdk_threads_init();
New linker / compiler flags are probably needed,
g++ -O -Wall test.cpp -lopencv_highgui -lopencv_core `pkg-config --libs --cflags gdk-2.0 gtk+-2.0`
After these changes there was still an occasional crash, so I added gdk_threads_enter() and gdk_threads_leave(); calls to test if they would help:
gdk_threads_enter();
namedWindow ((char *) arg, CV_WINDOW_AUTOSIZE);
gdk_threads_leave();
Since the crashing was not reproducible, it is hard to tell if those lines have any effect.