[Unit]
Description=Ekklesia Classroom presentation import
Documentation=file:///usr/local/bin/classroom-presentation-import
# Nothing graphical: it copies, converts and renders files. It is a user
# service rather than a system one because the downloads it watches and
# the library it fills both belong to the classroom account, and a root
# service writing into a teacher's home would have to be told about every
# one of those permissions.
PartOf=graphical-session.target

[Service]
ExecStart=/usr/local/bin/classroom-presentation-import
# It exits 0 immediately on a device with PRESENTATIONS_ENABLED=false, and
# on-failure means such a device is left alone rather than restarted in a
# loop forever. A device that does have Presentations gets the watcher
# back if it ever dies, because a teacher whose download never appears has
# no way at all to find out why.
Restart=on-failure
RestartSec=10
Slice=session.slice
# LibreOffice converting a large deck must never be what a teacher notices
# about the machine. The room's own applications come first; this is the
# only thing here that is allowed to take a while.
Nice=10
IOSchedulingClass=idle

# MEMORY. Measured in the lab, LibreOffice converting one deck: 203 MB
# for ten slides of text, 738 MB for thirty slides sharing twelve photos,
# 1.4 GB for thirty different photos and 2.1 GB for twenty very large
# ones, for twenty seconds or so. A 4 GB classroom running Plasma and
# Wonder Ink does not have 2 GB spare, and in testing the kernel killed
# the whole service mid-conversion — which then restarted and tried the
# same deck again, while the library said "Getting this ready" for ever.
#
# At most 40% of this machine's memory: 1.6 GB on 4 GB, 3.2 GB on 8 GB.
# A deck that needs more is stopped HERE, inside this service, rather
# than pushing the teacher's own windows out of memory.
MemoryMax=40%
# If memory runs short everywhere, this is what goes first: never the
# lesson on the screen, the browser or the panel.
OOMScoreAdjust=800
# And a killed LibreOffice is a failed import, not a dead service. The
# watcher records it — "needed more memory", with Try again — and carries
# on. systemd's default stops the whole unit when any one process in it
# is killed for memory.
OOMPolicy=continue

[Install]
WantedBy=plasma-workspace.target