The following is current flow when classifying tracker: 1. [Main Thread]AsyncUrlChannelClassifier prepares the features for blacklist and invoke AsyncClassifyLocalWithFeatures(). The classify task is then handed over to the URL classifier worker thread. 2. [Worker Thread]url classifier worker thread checks if the URL is in the tables and calls back the result to the main thread. 3. [Main Thread] If the URL is found in the blacklist, prepare the features for whitelist and invokes AsyncClassifyLocalWithFeatures again. 4. [Worker Thread]url classifier worker thread checks if the URL is in the tables and calls back. 5. [Main Thread]AsyncUrlChannelClassifier process the result. Baku may have an idea about how to avoid the extra step 3.

This is not related to the recent changes of AsyncClassifyLocalWithFeatures API. The behavior has existed for a long time and maybe we could optimize it with recent changes. But I did want to not rush to fix this because we have changed a lot of stuff recently and it will be safer to make sure everything is stable before optimization.

ah, I just realized that this should be the same one as Bug 1516133