Add batch predictor

[sailist]

It's not very convenient when do batch inference by using original detectron2 api, the solution provided here #282 (comment) is good, and I extended it's code to support more forms.

[facebook-github-bot]

Hi @sailist!

Thank you for your pull request and welcome to our community.

Action Required

In order to merge any pull request (code, docs, etc.), we require contributors to sign our Contributor License Agreement, and we don't seem to have one on file for you.

Process

In order for us to review and merge your suggested changes, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

Once the CLA is signed, our tooling will perform checks and validations. Afterwards, the pull request will be tagged with CLA signed. The tagging process may take up to 1 hour after signing. Please give it that time before contacting us about it.

If you have received this in error or have any questions, please contact us at cla@fb.com. Thanks!

[facebook-github-bot]

Thank you for signing our Contributor License Agreement. We can now accept your code for this (and any) Facebook open source project. Thanks!

[ashnair1]

@sailist Have you tried using this BatchPredictor with AsyncPredictor?

[sailist]

Fine, I'll try it, thanks.

[Sorakuhaku]

Can you add unit test to ensure it is working properly?

[ppwwyyxx]

As the doc of DefaultPredictor mentions, it is only for simple demo purposes and we do not plan to extend it with new capabilities. Users are expected to use the model object following its formats (which supports batch predictions) if more complicated logic is needed.