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feat(ipc): control socket stage 2 - wake the render thread, brightness.set, plugin.reload (#720)

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Control socket stage 2: the render thread wakes for queued commands (static screens ~1 ms, Vegas within one frame), brightness.set, and plugin.reload after a store update, with mailbox/restart fallbacks. Rig checks listed in the PR body are still to run.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Chuck
2026-10-01 20:37:54 -04:00
committed by GitHub
co-authored by Claude Opus 5.5
parent f72d69c2b0
commit 746dcfcadb
22 changed files with 1998 additions and 119 deletions
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docs/IPC_CONTROL_SOCKET.md
+168 -35
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@@ -2,14 +2,16 @@
The display process serves a Unix socket that the web interface uses to send
it commands and get an answer back. It replaces the cache-file "mailboxes" on
the SD card one command at a time. Stage 1, described here, carries on-demand
start/stop/status. The file mailbox stays as a fallback for one release.
the SD card one command at a time. Stage 1 carries on-demand start, stop and
status. Stage 2 makes those commands land within a frame on every kind of
screen, and adds `brightness.set` and `plugin.reload`. The file mailbox stays
as a fallback for one release.
| | |
|---|---|
| Socket | `/run/ledmatrix/control.sock` (tmpfs) |
| Served by | the display process ([`src/ipc/server.py`](../src/ipc/server.py)), started by `DisplayController.run()` |
| Used by | the web interface ([`src/ipc/client.py`](../src/ipc/client.py)): `POST /api/v3/display/on-demand/start` and `/stop` |
| Used by | the web interface ([`src/ipc/client.py`](../src/ipc/client.py)): `POST /api/v3/display/on-demand/start` and `/stop`, `POST /api/v3/plugins/update` (reload), `POST /api/v3/config/main` (brightness) |
| Contract | [`src/ipc/contract.py`](../src/ipc/contract.py): messages, versions, framing and the socket path; both sides import it |
| Override | `LEDMATRIX_CONTROL_SOCKET=/some/path.sock` for both processes, or `=off` to disable it |
@@ -71,6 +73,8 @@ one. Clients branch on `error.code`, never on the message text.
| `on_demand.start` | `{plugin_id?, mode?, duration?, pinned?}` (at least one of `plugin_id` and `mode`) | ack | queued |
| `on_demand.stop` | — | ack | queued |
| `on_demand.status` | — | `{on_demand: {...}, current_mode, display_active}` | answered directly |
| `brightness.set` | `{brightness: int 0-100}` | `{brightness, panel_brightness, dimmed, display_active}` | queued, awaited (2 s) |
| `plugin.reload` | `{plugin_id}` | `{plugin_id, reloaded: true, version, modes}` | queued, awaited (10 s) |
`duration` is a number of seconds, or a numeric string. `0`, `null` or `""`
mean "until stopped". `pinned` must be a real boolean: the REST route has
@@ -78,28 +82,59 @@ already converted strings like `"false"` before it sends the command. The
`on_demand` object in `on_demand.status` is the same dict the display
publishes to `display_on_demand_state`.
**Acknowledgements.** A queued command is *accepted*, not *done*.
`brightness.set` sets the panel's normal brightness. It is transient: it
writes nothing to `config.json`, and the next config the display's watcher
loads (or a restart) puts the configured value back. The web interface
sends it after it has saved the setting, so the two agree. The dim schedule
still applies on top, so `panel_brightness` is the dim level while the
schedule dims. While the schedule has the display off, the new level is
kept for when it comes back on.
`plugin.reload` loads a plugin the display is running again from disk,
manifest included: the steps of disabling it live and enabling it again,
with its modes kept in their place in the rotation. Only a running plugin
can be reloaded (`not_loaded` otherwise), so the id never makes the display
import anything new. A plugin loaded only for an on-demand session gets
`busy`. A new version that fails to load gets `failed` and stays out of the
rotation, as it would after a restart.
**Acknowledgements.** A queued on-demand command is *accepted*, not *done*.
`{"accepted": true, "request_id": …}` means the command is waiting in the
render thread's queue, and the render thread will apply it at its next
on-demand check. That is within one frame on a scrolling screen, 0.25 s
during a dwell, and up to 1 s on a static screen, whose frame loop sleeps a
second between frames. Except on a scrolling screen, where the mailbox waits
up to 0.25 s, these are the mailbox's delays too: stage 1 adds
acknowledgements, not speed. Any outcome is published as before
render thread's queue. Since stage 2 the render thread waits on that queue
instead of sleeping, so it applies the command within one frame on every
kind of screen (see below). Any outcome is published as before
(`display_on_demand_state`, and `status`/`error` for a bad plugin or mode),
and it can be read with `on_demand.status`.
**Awaited commands.** `brightness.set` and `plugin.reload` are answered only
once the render thread has applied them, with their result or their error.
The connection thread waits for that (2 s and 10 s, `AWAIT_SECONDS` in the
contract); the render thread never waits for a client. When the render thread
has not got to the command in time, the answer is `pending`: the command
stays queued and is still applied, so a client treats `pending` as "not known
to be done", not as a refusal. The client's own timeout is one second longer
than the display's wait, so `pending` arrives before the client gives up.
**Versions.** Every request carries `v`. For any command except `hello`, a
`v` the display does not speak gets `unsupported_version`. `hello` is checked
by its `versions` list instead, and its result names the highest version both
sides share, so a client can find out what a display supports before it
relies on anything newer. Stage 1's client sends `v: 1` and falls back to the
relies on anything newer. The client sends `v: 1` and falls back to the
mailbox when the display refuses it. It does not send `hello` first, which
saves a round trip.
New commands are added within a version, so stage 2 is still version 1. A
display that does not know a command answers `unknown_command`, which the
web interface treats like any other socket failure and falls back from, and
`hello` lists the commands a display knows. The version changes only when the
envelope or the meaning of an existing command changes.
**Error codes:** `bad_json`, `bad_request`, `message_too_large`,
`unsupported_version`, `unknown_command`, `invalid_args`, `busy` (queue full,
or too many connections), `forbidden` (peer credentials refused), `internal`.
Stage 2 adds `pending` (accepted, not applied in time, still queued),
`not_loaded` (`plugin.reload` of a plugin the display is not running) and
`failed` (the render thread tried, and it did not work).
Try it on a device:
@@ -107,6 +142,7 @@ Try it on a device:
python3 - <<'EOF'
from src.ipc import client # run from the project directory
print(client.on_demand_status())
print(client.brightness_set(60))
EOF
```
@@ -116,19 +152,71 @@ The server's threads never touch rendering. A connection thread parses the
request, validates it against the contract, and then does one of two things:
- For a command that changes the panel, it puts a `QueuedCommand` on a
bounded queue (16 entries) and answers with the ack.
bounded queue (16 entries) and answers with the ack, or, for an awaited
command, with the outcome the render thread reports back through the
command's `CommandOutcome`.
- For a query, it answers from a status snapshot the display provides
(`DisplayController._control_status`). The snapshot only reads attributes.
The render thread drains the queue in `_poll_on_demand_requests()`, the same
place it reads the mailbox, and hands each command to
`_handle_on_demand_request()`, which is the mailbox's own handler. The two
paths share all of their code: activation, the processed-id guard, error
publishing, and resuming the rotation afterwards. The 0.25 s floor on the
mailbox read does not apply to the queue, because draining it costs no disk
read. A queued command also lets `_service_pending_changes()` skip its own
floor, so a long scrolling screen or a Vegas iteration takes the command at
its next frame.
place it reads the mailbox:
- An on-demand command goes to `_handle_on_demand_request()`, which is the
mailbox's own handler. The two paths share all of their code: activation,
the processed-id guard, error publishing, and resuming the rotation
afterwards.
- `brightness.set` is applied there and then (`_apply_control_brightness`),
and the current frame is pushed again so the panel shows it.
- `plugin.reload` waits for the top of the next loop pass, the place where
plugins are enabled and disabled live, because there no `display()` and no
Vegas iteration is on the stack (`_apply_pending_plugin_reloads`). Until
then the current screen ends early, as it does for a WiFi notice: the
frame loops, the dwell and Vegas's interrupt check all treat a pending
reload as a reason to stop (`_screen_preempted`). The rotation then
advances, and the next pass reloads before it draws.
The 0.25 s floor on the mailbox read does not apply to the queue, because
draining it costs no disk read. A queued command also lets
`_service_pending_changes()` skip its own floor.
### Waking the render thread (stage 2)
Stage 1 made the socket answer, but not land sooner: a queued command waited
for the same polls the mailbox does. Measured on ledpi (Pi 4, 24 fps Vegas),
a start took 1.02 s on a static screen and about 0.4 s in Vegas either way.
Now the queue wakes the render thread:
- **The waits.** The server sets a `threading.Event` whenever it queues a
command. The render thread waits on it (`ControlServer.wait_for_command`)
where it used to sleep: the static screen's 1 s frame sleep
(`_wait_frame_interval`) and the dwell's 0.25 s ticks
(`_sleep_with_plugin_updates`, which also covers scheduled-off and the
empty-rotation pause). On a wake it applies the command at once. A command
that does not end the screen, such as a brightness, does not cut the frame
short: the wait carries on to the end of the interval, so the plugin is
still drawn once a second.
- **Vegas.** The coordinator still runs its interrupt check every 10 frames,
and now also at any frame where `urgent()` is true. The display passes
"a control socket command is queued", which is one `Event.is_set()` per
frame.
- **Scrolling screens** already service pending changes every frame.
So a command lands within a millisecond or so on a static screen and in a
dwell, and within one frame in Vegas and on a scrolling screen. The mailbox
keeps its old delays. Commands still run only on the render thread: the
connection threads only queue them and set the event.
The waits are timed `Event.wait()` calls: no polling, and no more wake-ups
than the sleeps they replace when nothing arrives. Measured under WSL
(Python 3.12, 20 s runs in the order before, after, after, before, with the
socket's accept thread up), the idle process used 0.015–0.018% of a core
before and 0.019–0.021% after on a static screen, and 0.035–0.037% before and
0.047% after in a dwell: about 25 µs more per wait, from `Event.wait`'s own
bookkeeping. A client's send to the render thread waking took 0.72 ms median
(1.04 ms max), and a whole `brightness.set` round trip 0.64 ms median.
Without a socket (Windows, `LEDMATRIX_CONTROL_SOCKET=off`) the waits are the
plain sleeps they were.
**Exactly once.** A command and a mailbox write for the same request share
one `request_id`. If the client times out after the display queued the
@@ -154,6 +242,11 @@ block the render loop or crash it:
- **Full queue.** When the queue is full, the client gets `busy` and falls
back to the mailbox. A full queue means the render thread is stuck, and the
systemd watchdog deals with that.
- **Awaited commands.** The wait for an awaited command's outcome happens on
its connection thread and is bounded (`AWAIT_SECONDS`), so a stuck render
thread costs that client `pending` and one connection slot for at most
10 s. The render thread settles an outcome without blocking; one nobody is
waiting for any more is simply dropped.
- **Startup.** The server binds under a temporary name, sets the mode and the
group, then renames the socket into place, so it never appears with the
umask's permissions. It removes a stale socket (a file that nothing is
@@ -191,9 +284,13 @@ anything else in the group they share:
and is disconnected. This covers a socket mode that someone loosened by
hand.
The commands are deliberately narrow. Stage 1 can start or stop on-demand
display and read its state, which anyone who can reach the web UI can already
do. Nothing on the socket runs a shell, writes a file, or names a path.
The commands are deliberately narrow. They start or stop on-demand display,
read its state, set the brightness, and reload a plugin the display is
already running, all of which anyone who can reach the web UI can already do
(the last by restarting the display). Nothing on the socket runs a shell,
writes a file, or names a path, and `plugin.reload` cannot make the display
import a plugin it was not running. Stage 2 changed none of the access rules
above.
**Development.** A display that is not root and cannot write to
`/run/ledmatrix`, such as `python3 run.py -e` from a checkout, serves the
@@ -205,28 +302,49 @@ device never touches the live display.
## Stage plan
1. **On-demand, with acks (this stage).** Contract, server, client.
1. **On-demand, with acks (done, #706).** Contract, server, client.
`on_demand.start`/`stop`/`status`, `hello`, `ping`. The REST routes try the
socket first and report `transport: "socket" | "mailbox"` (plus
`socket_error` on fallback). The mailbox is unchanged, and the plugins that
write it directly (birdnet-go, mqtt-notifications, on-air, pomodoro-timer)
keep working.
2. **Commands that are restarts or polls today.**
- `brightness.set`, transient and with no `config.json` write.
2. **Commands that were restarts or polls (done).**
- The render thread waits on the queue instead of sleeping, and Vegas
checks it every frame, so a command lands within a frame on every kind
of screen (see "Waking the render thread").
- `brightness.set`, transient and with no `config.json` write. `POST
/api/v3/config/main` sends it after saving a brightness and reports
`brightness_transport`; without the socket the config watcher applies
the saved value, as before.
- `plugin.reload`, which replaces the `restart_required` answer from #688
with a live reload of the updated plugin on the render thread.
- `config.reload`, which applies a saved config without waiting for the 2 s
mtime poll and acks which sections changed.
- The dwell sleep and the static screen's 1 s frame sleep wait on the
queue instead of sleeping, so a command lands within milliseconds on
every kind of screen. Under WSL, with a static plugin on screen, a stop
takes 1.0 s by either path today.
for a store update of an enabled plugin. `POST /api/v3/plugins/update`
answers `restart_required: false, reloaded: true` once the new code
runs, and falls back to the restart banner (with `reload_error`)
otherwise.
- `config.reload` was left out. Its only gain over the config watcher
would be skipping the watcher's 2 s mtime poll, and the one setting
where those seconds show, brightness, now has its own command. Plugin
settings already reach the running plugin through the watcher, and the
"which sections changed" ack had no reader: the web interface knows
what it saved. A reload from the socket thread would also run every
config subscriber on a second thread beside the watcher's.
3. **A state stream.** A `subscribe` command that keeps the connection open
and pushes events: mode changes, on-demand state, plugin runtime state and
the heartbeat. It replaces the polled `display_current_state`,
and pushes events: mode changes, on-demand state (including the outcome of
an acked on-demand command, which today is only published), plugin
runtime state, the outcome of a reload that answered `pending`, and the
heartbeat. It replaces the polled `display_current_state`,
`plugin_runtime_snapshot` (#690) and `display-heartbeat.json` (#687) for
readers that hold a connection. The web interface relays it to its
existing SSE stream. The files remain for one release for older readers.
- The server's per-connection threads (8 at most) do not suit long-lived
subscribers. A subscriber needs its own bound and a writer that drops
events for a slow reader rather than blocking the display.
- Events are produced on the render thread, so publishing must be a
non-blocking hand-off, like the queue in the other direction.
- The store's install of an already-enabled plugin, and an uninstall that
keeps its config, still answer `restart_required`. With the stream they
can use a load/unload command and report the result the same way the
update route does now.
4. **Retire the mailboxes.** After a release in which every device has had the
socket, the web interface stops writing `display_on_demand_request`, and
the display stops polling it, logging the plugins that still write it so
@@ -248,3 +366,18 @@ If the response says `"transport": "mailbox"`, `socket_error` gives the
reason. `no_socket` means the display is stopped or predates the socket.
`refused` usually means the web user is not in the socket's group, which
takes effect when the web service restarts after the user is added.
Brightness and a plugin reload:
```bash
curl -s -X POST localhost:5000/api/v3/config/main \
-H 'Content-Type: application/json' -d '{"brightness":40}'
# ... "brightness_transport": "socket"
curl -s -X POST localhost:5000/api/v3/plugins/update \
-H 'Content-Type: application/json' -d '{"plugin_id":"clock-simple"}'
# after a real update of an enabled plugin: "restart_required": false, "reloaded": true
sudo journalctl -u ledmatrix | grep -E "Brightness set|Reload(ing|ed) plugin"
```
`unknown_command` in `brightness_socket_error` or `reload_error` means the
display runs a stage-1 build: restart it once to pick up this one.