RFR: 8372344: QUIC transfer may deadlock if pacing rate is too high

[Volkan Yazici]

On Fri, 21 Nov 2025 21:41:29 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

> Modify the PacketTransmissionTask to update the current deadline (`now`) between loop iterations.
> 
> This fixes the deadlock issue which happened when the next deadline was equal to the current one, but no progress could be made because the pacer quota only increases as time passes.
> 
> No new test; the issue was extremely rare. Existing tests continue to pass.

@djelinski, amazing catch! :exploding_head:

I'd really appreciate it if you can share a bit about how you troubleshoot it. Which diagnostics knobs did you turn? Which log patterns made you suspect the `congestionController.updatePacer(now)` line?

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Marked as reviewed by vyazici (Committer).

PR Review: https://git.openjdk.org/jdk/pull/28462#pullrequestreview-3502128029