Don't poll auto-revert files that use notification (bug#35418)
It is a waste to periodically poll files that use change notification in auto-revert mode; stop doing that. If no files need polling, turn off the periodic execution entirely to further avoid wasting power. Use a timer to inhibit immediate reversion for some time after a notification, for throttling. This change does not apply to files in global-auto-revert-mode, where polling is still necessary. It is disabled by default, and enabled by setting `auto-revert-avoid-polling' to non-nil. * lisp/autorevert.el (toplevel): Require cl-lib. (auto-revert-avoid-polling, auto-revert--polled-buffers) (auto-revert--need-polling-p, auto-revert--lockout-interval) (auto-revert--lockout-timer, auto-revert--end-lockout): New. (global-auto-revert-mode): Keep notifiers for buffers in auto-revert mode. (auto-revert-set-timer): Use auto-revert--need-polling-p. (auto-revert-notify-handler): Restart polling if notification stopped. Use new lockout timer. (auto-revert-buffers): Use auto-revert--polled-buffers and auto-revert--need-polling-p. (auto-revert-buffers-counter, auto-revert-buffers-counter-lockedout): Remove. * etc/NEWS (Changes in Specialized Modes and Packages): Describe the new auto-revert-avoid-polling variable. * doc/emacs/files.texi (Reverting): Add paragraph describing auto-revert-avoid-polling.
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