Document Battery Optimization challenges on Android

* etc/PROBLEMS (Runtime problems specific to Android): Mention
battery optimization, the way it impacts background execution,
and how it might be disabled.

diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index ebecf50d26b176124de39d9d45154b9a0e1ab2a2..72a6639c97808037f33a72000bdcb708cf21cf71 100644 (file)
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -3567,6 +3567,27 @@ port is a large undertaking that we are looking for volunteers to
 perform.  If you are interested in taking responsibility for this
 task, please contact <emacs-devel@gnu.org>.
 
+** Emacs can only execute spasmodically in the background.
+
+Recent Android releases impose "battery optimization" on programs for
+which it is not expressly disabled; such optimization inhibits the
+execution of background services outside brief windows of time
+distributed at intervals of several dozens of minutes.  Such programs
+as ERC which must send "keep-alive" packets at a rate beyond that at
+which these windows arrive consequently lose, yielding connection
+timeouts after Emacs has been in the background long enough that
+battery optimization enters into effect.
+
+This optimization can be disabled through the Settings app: navigate
+to "Apps & notifications", "Emacs", "Battery", "Battery Optimization",
+before clicking the drop-down menu labeled "Not Optimized", selecting
+the option "All Apps", scrolling to "Emacs", clicking on its entry and
+selecting "Don't Optimize" in the dialog box thus displayed.
+
+The organization of the Settings app might disagree with that
+illustrated above, which if true you should consult the documentation
+or any search mechanism for it.
+
 * Build-time problems
 
 ** Configuration