Fundamentals, Object Lifetime should mention non-parent–child relationships object destruction order

[zopsicle]

Fundamentals, Object Lifetime reads:

Applications can free or destroy objects in any order, except that parent objects must be freed only after all child objects are freed. An object is the parent of another child object if the parent was used as the first object parameter in the creation of the child.

A reader may now conclude that they do not need to worry about destruction order, except for the parent–child relationship. For example, they may conclude that they may destroy an image before destroying an image view created from the image, as the parent–child relationships are device–image and device–image-view.

But there is another exception to the "any order" permission, through Fundamentals, Valid Usage for Object Handles:

Any input parameter to a command that is an object handle must be a valid object handle, unless otherwise specified. An object handle is valid if:

• Any objects used by that object, either as part of creation or execution, must also be valid.

together with VUID-vkDestroyFooBar-fooBar-parameter, such as for image views:

VUID-vkDestroyImageView-imageView-parameter
If imageView is not VK_NULL_HANDLE, imageView must be a valid VkImageView handle

As such, Fundamentals, Object Lifetime should not suggest any order is allowed, because it is not.

[spencer-lunarg]

I was under the impression that you can destroy in any order... it is very valid to call vkDestoryImage and now any VkImageView is "invalid" and if you try to use it other than destroying it, the Validation Layers will yell at you

I guess what is core issue/example of where you are seeing problems

[zopsicle]

Thanks for the response.

I was under the impression that you can destroy in any order

That's interesting! In that case I'd say the handle validity requirements in certain destroy functions need to be relaxed.

Consider the following:

1. Create imageView from image.
2. Destroy image.

   • image is no longer a valid handle:

     An object handle is valid if: It has not been deleted or freed by a previous call to the API.

   • imageView is also no longer a valid handle:

     An object handle is valid if: Any objects used by that object, either as part of creation or execution, must also be valid.

     assuming that image is considered used by imageView as part of creation.

3. Destroy imageView.
   • This is invalid usage:

     If imageView is not VK_NULL_HANDLE, imageView must be a valid VkImageView handle

I guess what is core issue/example of where you are seeing problems

I'm just trying to understand if I have to worry about destruction order, and find that the spec is inconsistent.

[Tobski]

The fundamentals chapter already states that this is supposed to be fine, we just need to change how the destroy VUs are written I think.

I think we just need to change these two VUs:

VUID-vkDestroyImageView-imageView-parameter
If imageView is not VK_NULL_HANDLE, imageView must be a valid VkImageView handle

VUID-vkDestroyImageView-imageView-parent
If imageView is a valid handle, it must have been created, allocated, or retrieved from device

to a single VU:

VUID-vkDestroyImageView-imageView-parent
If imageView is not VK_NULL_HANDLE, it must have been created, allocated, or retrieved from device

(And replicate for all destroy commands)