It's possible to get chickenpox more than once, but it is very unusual.
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The primary signal is desiredSize on the controller. It can be positive (wants data), zero (at capacity), negative (over capacity), or null (closed). Producers are supposed to check this value and stop enqueueing when it's not positive. But there's nothing enforcing this: controller.enqueue() always succeeds, even when desiredSize is deeply negative.，更多细节参见同城约会
I profiled the code with and without the type hint. The encoding time dropped from 31µs to 4µs.