NullReferenceException in LargeArrayPool.cs line 36

[bastiankayser]

Describe the bug

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=Microsoft.Azure.Kinect.Sensor
  StackTrace:
   at Microsoft.Azure.Kinect.Sensor.LargeArrayPool.Rent(Int32 minimumLength) in D:\a\1\s\extern\Azure-Kinect-Sensor-SDK\src\csharp\SDK\LargeArrayPool.cs:line 36
   at Microsoft.Azure.Kinect.Sensor.Allocator.AllocateFunction(Int32 size, IntPtr& context) in D:\a\1\s\extern\Azure-Kinect-Sensor-SDK\src\csharp\SDK\Allocator.cs:line 317

To Reproduce
I get depth images from the sensor and use a transform to create the point cloud from the depth image. The code looks like the following:

using (Capture capture = AzureKinect.GetCapture())
{
	var targetArray = new Int16[depthImage.HeightPixels * depthImage.WidthPixels*3];
	var pointCloudImage = transform.DepthImageToPointCloud(capture.Depth, CalibrationDeviceType.Depth);
	
	unsafe
	{
		using (var pin = pointCloudImage.Memory.Pin())
		{
			fixed (void* targetArrayPointer = &targetArray[0])
			{
				Buffer.MemoryCopy(pin.Pointer, targetArrayPointer, targetArray.Length*2,
					pointCloudImage.Size);
				
	
			}
	
		}
	
	}
	captureDepth.Dispose();
}

This works for some time but eventually throws the NullReferenceException.

Expected behavior
No NullReferenceException

Desktop (please complete the following information):

• OS with Version: Windows 10 Pro Build 18363
• SDK Version: 1.2.0 (nuget package
• Firmware version:
  Current Firmware Versions:
  RGB camera firmware: 1.6.102
  Depth camera firmware: 1.6.75
  Depth config file: 6109.7
  Audio firmware: 1.6.14
  Build Config: Production
  Certificate Type: Microsoft

[ahoink]

Happens to me too, but only on rare occasions. I'm using SDK version 1.3.0 from the nuget package. Camera firmware is all the same as the original post.

[CameronVetter]

Same here, on rare occassion I end up in this code:

                if (x.IsAlive)
                {
                    buffer = (byte[])x.Target;
                    if (buffer.Length >= minimumLength)
                    {
                        _ = this.pool.Remove(x);
                        return buffer;
                    }
                }

x.isAlive will be true for the if condition but by the time the buffer assignment happens isAlive is false and Target is null. Seems like there is a thread safety issue here.

[robharrisonuk]

I've just had this problem and it was due to the garbage collector being called on another thread after the x.IsAlive test and before buffer is assigned. My fix was to test if buffer is null before using it (which according to the WeakReference docs is a valid test - also see https://stackoverflow.com/questions/1687045/thread-safety-of-weakreference)