Use optimistic locking where possible in ResponseBodyEmitter

[lucky8987]

1. Use CAS instead of synchronized to set the complete state.
2. Reduce the synchronized range added by the callback function.

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[simonbasle]

Thanks for the PR @lucky8987, this looks like a good performance improvement. That close to the release, I'll review it a bit more in depth and discuss it with other team members, but I expect this should make the cut 👍

[lucky8987]

Thanks for the PR @lucky8987, this looks like a good performance improvement. That close to the release, I'll review it a bit more in depth and discuss it with other team members, but I expect this should make the cut 👍

OK，this is my first PR and I'm really looking forward to it being accepted.

[simonbasle]

@lucky8987 good news, then: it's been merged 😉