/// <summary>
/// Retrieves a native image handle from the native API.
/// </summary>
/// <param name="nativeMethod">Native method to retrieve the image.</param>
/// <param name="cachedImage">A cached instance of the Image that we return to callers. (Callers may dispose this image, although they shouldn't).</param>
/// <remarks>
/// 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, we construct a new wrapper and dispose the old one.
/// If existing wrapper has been disposed, we throw an exception.
/// </remarks>
private void UpdateImageWrapperAndDisposePrevious(
Func <NativeMethods.k4a_capture_t, NativeMethods.k4a_image_t> nativeMethod,
ref Image cachedImage)
{
// 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));
}
// Get the image object from the native SDK
// We now own a reference on this image and must eventually release it.
NativeMethods.k4a_image_t nativeImageHandle = nativeMethod(this.handle);
// This try block ensures that we close image (and release our reference) if we fail
// to create a new Image.
try
{
// If this Capture previously had an image
if (cachedImage != null)
{
// Get the native pointer
IntPtr imageHandleValue = nativeImageHandle.DangerousGetHandle();
// Get the handle value from the cached image. If it has been disposed, this
// will throw an exception, which will be passed to the caller.
// Take an extra reference on the cachedImage to ensure it doesn't get disposed
// after getting the IntPtr from the handle.
using (Image reference = cachedImage.Reference())
{
if (reference.DangerousGetHandle().DangerousGetHandle() != imageHandleValue)
{
// The image has changed, invalidate the current image and construct new wrappers
cachedImage.Dispose();
cachedImage = null;
}
}
}
if (cachedImage == null && !nativeImageHandle.IsInvalid)
{
// Construct a new wrapper and return it
// The native function may have returned
#pragma warning disable CA2000 // Dispose objects before losing scope
cachedImage = new Image(nativeImageHandle);
#pragma warning restore CA2000 // Dispose objects before losing scope
// Since we have wrapped image, it is now owned by Image and we should no longer close it
nativeImageHandle = null;
}
}
finally
{
// Ensure the native handle is closed if we have a failure creating the Image object
if (nativeImageHandle != null)
{
nativeImageHandle.Close();
}
}
}
}
// 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 <NativeMethods.k4a_capture_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);
}
}