// This function retrieves a native image handle from the native API.
//
// If this is the first time calling the property, we construct a new wrapper
// If the handle is for an Image we have already constructed a wrapper for, we return the existing wrapper
// If the handle is for a different Image, or if the wrapper has already been disposed, we construct a new wrapper and dispose the old one
private Image GetImageWrapperAndDisposePrevious(Func <BodyTrackingNativeMethods.k4abt_frame_t, NativeMethods.k4a_image_t> nativeMethod,
ref Image cache)
{
// Lock must be held to ensure the Image in cache is not replaced while we are inspecting it
// It is still possible for that Image to be accessed or Disposed while this lock is held
lock (this)
{
if (this.disposedValue)
{
throw new ObjectDisposedException(nameof(Capture));
}
NativeMethods.k4a_image_t image = nativeMethod(this.handle);
// This try block ensures that we close image
try
{
if (cache != null)
{
IntPtr imageHandle = image.DangerousGetHandle();
// Only attempt to access cache in this try block
try
{
// If cache was disposed before we called the native accessor (by the caller or another thread),
// the handle could have been reused and the values would incorrectly match. However, cache.DangerousGetHandle()
// will throw an exception, and we will correctly construct a new image wrapper.
if (cache.DangerousGetHandle().DangerousGetHandle() != imageHandle)
{
// The image has changed, invalidate the current image and construct a new wrapper
cache.Dispose();
cache = null;
}
}
catch (ObjectDisposedException)
{
// If cache has been disposed by the caller or another thread we will discard
// it and construct a new wrapper
cache = null;
}
}
if (cache == null && !image.IsInvalid)
{
// Construct a new wrapper and return it
// The native function may have returned
cache = new Image(image);
// Since we have wrapped image, it is now owned by the UnsafeImage object and we should no longer close it
image = null;
}
}
finally
{
// Ensure the native handle is closed if we have a failure creating the Image object
if (image != null)
{
image.Close();
}
}
return(cache);
}
}
internal Image(NativeMethods.k4a_image_t handle)
{
this.handle = handle;
}
