“User initiated user” means that the user has requested this operation directly and is likely to wait, but the user interface itself does not depart from the result. "Get new tweets because the user has done a pull-to-refresh or recounted hint. These things should happen quickly, but not right away. Once the calculation is complete, you probably won't request it again right away.
“User interactive” means that the user interacts directly with the result of this operation in real time. The user interface should get the result right now, or there will be a lag. You will probably request this operation quickly and repeatedly. This is the highest priority.
. " GCD" .