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imshow() not working in pthread MacOSX 10.9

asked 2014-03-24 21:12:04 -0500

Marco Leopardi gravatar image

updated 2014-03-24 21:12:49 -0500

Hello guys, here's my problem: on ubuntu 12.04 LTS with OpenCV 2.4.8 the following code works at 100%, in MacOSX (10.9.1), lastest version of Xcode (5.1) and OpenCV 2.4.8 i get a fully blank image and the program hang, if i move the cursor over the blank image i can see it "spinning" and the only way to stop the program is pushing the stop button on the Xcode interface. Another info: imwrite() within a thread works perfectly.

 void* test(void* arg);

 int main( int argc, char **argv )
 {

 Mat I = imread("/Users/Admin/Documents/X-Code/TestOpenCV/coin1.jpg", 1);
 imshow("1", I);
 waitKey();

 Mat I2 = imread("/Users/Admin/Documents/X-Code/TestOpenCV/coin2.jpg", 1);

 pthread_t h;
 pthread_create(&h, NULL, test, (void*)&I2);
 pthread_join(h, NULL);


 return 0;
 }

void* test(void* arg){

    imwrite("/Users/Admin/Documents/debug.jpg", *((Mat*)arg)); // WORKS!
    imshow("2", *((Mat*)arg)); // HANGS ON MACOSX
    waitKey();

    return NULL;
}
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answered 2014-03-24 21:22:46 -0500

updated 2014-03-26 20:32:20 -0500

You might need to initialize the visualization window before creating the thread with

cv::namedWindow("2");

[UPDATE]

Also, inside the thread function you should do:

pthread_exit(NULL);

Instead of

return NULL;

To comply with POSIX threads specifications.

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Thanks for your answer, this help but do not solve the problem, because i'm now able to show the image, but if i call waitKey() it hangs like before, so there is still something wrong...

Marco Leopardi gravatar imageMarco Leopardi ( 2014-03-25 06:50:31 -0500 )edit

I have updated my answer, please check it out

Martin Peris gravatar imageMartin Peris ( 2014-03-26 20:29:19 -0500 )edit
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answered 2014-03-24 21:59:34 -0500

unxnut gravatar image

imshow is not thread safe. You may want to move it to a point after the thread's termination.

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Thanks for your answer, unfortunately i need this for a video stream, i cannot call it after thread termination. Can you propose something that might work? (i repeat in Ubuntu that code work flawlessly)

Marco Leopardi gravatar imageMarco Leopardi ( 2014-03-25 06:23:04 -0500 )edit

Typically, you will synchronize the threads. Perform imshow just after the synchronization.

unxnut gravatar imageunxnut ( 2014-03-25 08:24:45 -0500 )edit
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Asked: 2014-03-24 21:12:04 -0500

Seen: 3,381 times

Last updated: Mar 26 '14