A Warning: OpenCV Memory Leaks

Technical Java
1

Hopefully this isn’t old news to everyone…
Our code was running fine at SFR but once we got the robot unbagged at SVR it kept crashing every ~30 seconds after code start with an OpenCV memory allocation error. Thanks to the wonderful CSAs here, we figured out that we had a memory leak in our custom camera streaming/ switching code (cscore’s UsbCameras, etc…). If you’re doing anything with Mats for camera streaming or vision, make sure you use

mat.release();

once you’re done with it. You can check your free roboRIO RAM in the second tab of driver station.

2

Better yet, avoid allocating Mat objects in a loop if at all possible. Pre-allocate and reuse.

3

As far as know you can’t do that with cscore’s CvSink/Sources… Am I wrong?

4

You will see in my previous post to the java-2-lifecams thread that it is feasible to resuse a mat. Not certain, perhaps because I avoided ever calling .setSource() ?

5

Here’s a fragment of our Java code where we create a Mat before entering the loop, then use imageSink.grabFrame to populate the Mat on each iteration:

    CvSink imageSink = new CvSink("CV Image Grabber");
    imageSink.setSource(camera);

    // All Mats and Lists should be stored outside the loop to avoid allocations
    // as they are expensive to create
    Mat inputImage = new Mat();

    GripPipeline pipe = new GripPipeline();

    // Infinitely process image
    while (true) {
	// Grab a frame. If it has a frame time of 0, there was an error.
	// Just skip and continue
	long frameTime = imageSink.grabFrame(inputImage);
6

Doh! Thanks, I missed that.

7