# kernel
## Thread-safe stdout routing
[`_StdoutRouter`](https://drscotthawley.github.io/boopiter/kernel.html#_stdoutrouter)
is installed once as the process’s real `sys.stdout`/`sys.stderr` and
dispatches each write to a *per-thread* target – so cells running on
different threads never cross-contaminate each other’s output, and
ordinary prints still reach the console.
## Building output blocks
Helpers that turn raw execution output into the ordered list of display
blocks a cell stores:
[`_collapse_cr`](https://drscotthawley.github.io/boopiter/kernel.html#_collapse_cr)
flattens `\r`-overwritten progress bars,
[`_best_block`](https://drscotthawley.github.io/boopiter/kernel.html#_best_block)
picks the richest MIME rendering of a result, and
[`_flush_figures`](https://drscotthawley.github.io/boopiter/kernel.html#_flush_figures)
captures any still-open matplotlib figures as PNGs.
## Running code synchronously
[`run_code`](https://drscotthawley.github.io/boopiter/kernel.html#run_code)
executes a cell’s source in the shared IPython shell and returns its
output blocks – the simple, blocking path.
------------------------------------------------------------------------
source
### run_code
``` python
def run_code(
src:str
)->list:
```
\*Execute `src` in the shared shell; return an ordered list of output
blocks (each a dict with ‘type’ – stream/error/display – and, for
display blocks, a ‘mime’ type). See Cell.output. Routes stdout/stderr
through \_StdoutRouter (same pattern as \_run_code_bg) rather than
IPython’s own capture_output(stdout=True), whose internal swap is a raw
global reassignment – letting this call and a concurrent \_run_code_bg
(different threads) safely capture their own output at the same time
instead of one clobbering the other’s capture window.\*
## Streaming from a background thread
For live output,
[`_run_code_bg`](https://drscotthawley.github.io/boopiter/kernel.html#_run_code_bg)
runs the same execution on a background thread with stdout/stderr tee’d
([`_TeeStream`](https://drscotthawley.github.io/boopiter/kernel.html#_teestream))
into a shared buffer, while
[`_RunState`](https://drscotthawley.github.io/boopiter/kernel.html#_runstate)
tracks the single in-flight run (only one cell executes at a time, like
a real kernel). `cells.py` polls this state to stream output to the
browser.