# plugins
## The plugin protocol
[`Plugin`](https://drscotthawley.github.io/boopiter/plugins.html#plugin)
is the base class: subclass it, set `name`/`icon`/`trigger`, and
implement `render()` for the hover popup (plus an optional always-on
background task).
[`register`](https://drscotthawley.github.io/boopiter/plugins.html#register)
is a class decorator that adds an instance to `PLUGINS`;
[`start_plugins`](https://drscotthawley.github.io/boopiter/plugins.html#start_plugins)
kicks off each one’s background task at server startup.
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### start_plugins
``` python
def start_plugins()->None:
```
*Call every registered plugin’s on_start() once. Wired into cells.py’s
@app.on_event(‘startup’) so background samplers spawn on real boot
only.*
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### register
``` python
def register(
cls
):
```
*Class decorator: instantiate `cls` and append it to PLUGINS.
Registration = importing this module. Returns `cls` unchanged.*
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### Plugin
``` python
def Plugin(
*args, **kwargs
):
```
*Base class for a top-bar plugin. Subclass it, set
`name`/`icon`/`trigger` (or in **init**), and override
`on_start`/`render` as needed; decorate the subclass with @register to
add it to PLUGINS. `icon` is ICONS-style path data (plain ‘d’ strings
and/or (d, scale) pairs) so cells.py renders it through the exact same
SVG machinery as its built-in icons. `trigger` is ‘hover’ (the only kind
wired up so far) or ‘click’.*
## The system-monitor plugin
The first concrete plugin:
[`SystemMonitor`](https://drscotthawley.github.io/boopiter/plugins.html#systemmonitor)
samples CPU/RAM/GPU/VRAM into ring buffers on a background thread and
renders them as
[`_sparkline`](https://drscotthawley.github.io/boopiter/plugins.html#_sparkline)
mini-charts in its popup. GPU comes from
[`_gpu_sample`](https://drscotthawley.github.io/boopiter/plugins.html#_gpu_sample)
shelling out to `nvidia-smi` (the same approach as
[`slmn.misc.gpu_free`](https://drscotthawley.github.io/slmn/misc.html#gpu_free))
on non-Mac hosts, or
[`_gpu_sample_darwin`](https://drscotthawley.github.io/boopiter/plugins.html#_gpu_sample_darwin)
reading Apple Silicon’s IOKit registry on macOS.
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### SystemMonitor
``` python
def SystemMonitor(
maxlen:int=300, interval:float=2.0
):
```
\*First plugin: continuously logs CPU%, system-RAM%, GPU-util%, and
VRAM% into ring buffers in the background (whether or not its panel is
open), and plots the accumulated history as inline-SVG sparklines when
hovered. GPU comes from nvidia-smi (\_gpu_sample) on non-Mac hosts or
the IOKit registry (\_gpu_sample_darwin) on macOS; VRAM is nvidia-only –
Apple Silicon’s unified memory has no separate pool to report. Rows just
go empty/‘–’ if unavailable, no separate placeholder needed.\*