Allow user to abort all active requests managed by a LoadingManager.

[gabrielcramer]

I needed this functionality and I think others will find it useful too. The possibility to abort can also be implemented just for a request ( The active request of a Loader). To accomplish this I was thinking about keeping a reference to the current XMLHttpRequest.

Here is an example with React:

class Example extends React.Component {

    constructor(props) {

        super(props);
        this.loadingManager = new THREE.LoadingManager();
        var texloader = new THREE.TextureLoader(this.loadingManager);
        // load textures

    }
    componentWillUnmount(){

        this.loadingManager.abortAllActiveRequests();

    }
}

[gabrielcramer]

There was also an inconsistency inside ImageLoader. It didn't pass its loading manager ( this.manager) to the XHRLoader created inside the load method. So the ImageLoader was calling the itemStart and itemEnd methods of its loading manager and the XHRLoader was calling the itemStart and itemEnd methods of the DefaultLoadingManager for the same call of the load method of the ImageLoader.

[mrdoob]

There was also an inconsistency inside ImageLoader. It didn't pass its loading manager ( this.manager) to the XHRLoader created inside the load method. So the ImageLoader was calling the itemStart and itemEnd methods of its loading manager and the XHRLoader was calling the itemStart and itemEnd methods of the DefaultLoadingManager for the same call of the load method of the ImageLoader.

I suspect this change has side effects. It tends to be better to keep PR simple and on topic.

[gabrielcramer]

I don't see what side effects it can have. The other loaders that use XHRLoader pass the loading manager. They let the XHRLoader call itemStart, itemEnd and itemError methods. Now if the load method of an ImageLoader is called these methods are called twice.

This was on topic. It's not possible to elegantly abort all active requests with two LoadingManagers ( DefaultLoadingManager always used by XHRLoader when created by ImageLoader and the one passed to the ImageLoader).

I think the PR is simple, just a few lines of code were modified.

[makc]

abortAllActiveRequests

within this particular manager, right? not all requests in application?

[gabrielcramer]

Yes, a loading manager can abort its active requests. Usually you don't use many loading managers in one application, but I'm open to suggestions. What do you think about the proposed solution to abort a single request (the current one of a loader)?

[makc]

Usually you don't use many loading managers in one application,

it's the opposite for me, every time when user wants to load another scene, I make new manager to have common onLoad callback for all the stuff. but, if this happens before previous scene was loaded, I had to resort to hacks in order to abort it.

What do you think about the proposed solution

I did not check the code, sorry.

[gabrielcramer]

I don't understand why you don't use the same loading manager. When the user wants to load another scene you just abort all the active requests and the onLoad callbacks won't be called. It seems like a clean solution to me.

I did not check the code, sorry.

I didn't write any code that enables the user to abort only a request. I just proposed to have a reference inside every loader to the current request, but I'm not sure if it is the best way to do it. Another way could be to return the request.

[makc]

to return the request

which was exactly what I did in #8091 and, because I went that easier way, I could not abort from the manager.

[mrdoob]

I think I would implement this in a different way. LoadindManager could have a items = [] array that gets populated when calling itemStart and depopulated when calling itemEnds. We would then just need abortAll() which would go through the current list and about everything.

[gabrielcramer]

Ok, sounds good, but it should be something like scope.manager.itemStart( url, request); with request as an optional parameter. ( when we have the url in Cache we don't pass a request to itemStart )
It would be nice to do this only in FileLoader, to pass the manager from ImageLoader to FileLoader and don't use it inside ImageLoader. Now a loading manager is used twice. ( a default loading manager is used inside FileLoader).

[gabrielcramer]

I created a new commit with your instructions, but I think the name of the method abortAll is not suggestive enough.

[Mugen87]

Um, I'm not sure LoadingManager.abortAll() is a good idea. To implement this method, it's necessary that LoadingManager has access to all active XMLHttpRequest request objects. However, ImageLoader does not load its images via FileLoader. It uses plain HTML image elements. These requests are currently not respected by this PR and thus can't be aborted (I think you can abort the loading of images by setting the src attribute to ""). But even if the requests of ImageLoader are respected in some way, ImageBitmapLoader needs a different processing since it uses fetch. I have the feeling all this makes an implementation quite complex.

[Mugen87]

Closing for now. This feature needs to be implemented differently if it is actually desired.