Use nfd.revents to indicates which event(s) may occur or have occurred.

[zhangyue-hashdata]

Use nfd.revents to indicates which event(s) may occur or have occurred.

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Change logs

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Does this PR introduce any user-facing change?

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Contributor's Checklist

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• [ ] Make sure your Pull Request has a clear title and commit message. You can take git-commit template as a reference.
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• [ ] List your communication in the GitHub Issues or Discussions (if has or needed).
• [ ] Document changes.
• [ ] Add tests for the change
• [ ] Pass make installcheck
• [ ] Pass make -C src/test installcheck-cbdb-parallel
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