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The last two handlers on the loop. Both were synchronous, so a member creating a
folder on a root that had spun down held the node for the spin-up, exactly as a
chunk read did.
Where a check and an act belong together they are now one call rather than two
awaits, and the single disk thread is what makes that atomic: `_mkdir_if_absent`
so two members creating the same name cannot both find nothing there and have
the second `mkdir` raise where a refusal was meant, and `_rmdir_if_empty` for
the reason the caller already re-tested emptiness — the first test happened
before a round trip to the operator's browser, and a file can land in between.
Two awaits would reopen that window one size smaller.
The guard is now the whole class rather than the calls that were fixed. It walks
the module's syntax tree and fails on any filesystem call outside the handful of
functions written to be run through `off_disk` — a new handler that stats a root
inline would pass every measured test, because those exercise the handlers that
exist today. Checked by putting a call back: it names the function and the line.
It leaves ffmpeg's own scratch files out, listed rather than silently allowed:
they are under `tempfile.mkstemp` on the system disk, not on a group root, so
they are not what spins down — but they do read a whole transcode into memory
from the loop, and the day that matters it is a different measurement from this
one.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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The rest of AV9's disk half. Serving a file left the loop in the commit before
this one; two paths were still on it.
**The availability poll.** `RootSet.refresh_availability` stats every root, and
eleven call sites reached it from `async def` — the reconcile loop among them, on
a timer. On a sleeping disk that is a stall once per tick, and the stat is also
what keeps the disk awake, so a node paid spin-up for a library nobody was
reading. All eleven now go through `off_disk`, `Root.is_live` included.
**The upload write.** `open`/`write`, and the resolve, the stat, the free-name
search, the rename and the unlink around it. This one could not simply be
awaited: the handler was synchronous, so nothing could come between the
`chunk_index != state.next_index` check and the `advance` that answers it, and
that is the whole of the chunk-ordering rule. Awaiting the write opens the gap —
chunk 1 arriving while chunk 0 is in the disk thread reads a position that has
not moved and is refused as out of order, so an upload would fail on a slow disk
and nowhere else. Verified, not assumed: without the lock the new ordering test
refuses three chunks of four.
So the check, the write and the advance are one critical section again, under a
lock held **per group**. Not per session: `partial_uploads` lives in the group
context so a reconnecting client finds its upload where it left it, which means
two sessions of one member share the position of one `.part` file. Arrival order
is preserved by construction — the dispatcher creates one task per message as it
arrives, tasks start in creation order, and the lock is the first thing each one
waits on, so its waiters queue in arrival order too.
`_do_file_upload` is a coroutine now, which is why forty-two test call sites gain
an `await`. Their outcomes are unchanged, file by file, against the run before
the change.
`test_ops.py` asked which public coroutines `ops` exposes and got `off_disk`,
imported rather than defined there. It now asks for the ones written in the
module, which is what its own docstring means; all forty-three operations are
still checked.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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A root that has spun down, or that lives on a network mount, answers its first
syscall in seconds rather than microseconds. Made from the event loop, that
stalls the whole node: no other group is served, no stream is fed, no chat
message is delivered and the hub socket is not read, for as long as the platter
takes to come back. It was found from the other end — a client's connection
attempt timing out on a node with one member, while the disk woke up — and it is
AV9's lesson with the disk in the place of the mail server.
Every filesystem call on a group's content now goes through `off_disk`, onto a
thread that belongs to that group's root set. The stat goes with the read: a stat
is what *wakes* a sleeping disk, so offloading only the read would move the stall
rather than remove it, and the read would then find the disk already awake.
`_locate` is the one place allowed to call `entry_abs_path`, which is
`Path.resolve()` and therefore syscalls too.
Five handlers touched: a chunk request, an audio transcode, a subtitle request, a
video stream and a delete. The delete became a coroutine, which its one caller
already was.
One worker per root set, not a pool and not one for the node. One worker for the
same reason the indexer's executor has one — two interleaved reads of a spinning
drive seek-thrash rather than go faster — and it keeps two threads from being
inside the same file at once, which is what makes the `seek`/`read` pair safe
without a lock. Per root set, because a node serves several groups and their
roots are not all on the same volume: a single worker would put one group's
sleeping USB drive in front of another's SSD, which is this symptom one level
down. The thread is created on the first read, so a group nobody downloads from
never starts one, and the daemon stops them all on the way out.
The tests measure rather than read: a ticker counts its own wake-ups beside a
request made slow on purpose, and a handler that blocks the loop takes every one
of them with it. Put either call back inline and both tests report zero wake-ups,
which was checked before they were trusted.
QUIC still reads on its loop. Its handler is synchronous by construction, no
client speaks it, and its distance from parity is already recorded in the design
document (§15.3, L3); moving it is part of bringing it to parity, not of this.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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