The four globals, two regimes¶

No self-check here — this page is the recap that ties the section together. If the previous pages held, this one should feel inevitable.

The four globals¶

A process has four things its threads cannot help but share, each covered by one page and one footman answer:

Global	The problem	footman's answer
working directory	one per process; chdir moves it for everyone	`ctx.cwd` as data; children get it at spawn; `footman.cwd()` in bodies
environment	one map; flows down only at spawn	each task owns a copy; reads, writes and deletes are its own
spawning	the child's world is fixed at spawn	`run()`/injection fill `cwd=`/`env=` per child, race-free
the terminal	one stdin, consumed not mutated	`ask()` and the `stdin` marker at the boundary; `interactive=True` to own it

The two regimes¶

The parallel regime is the default: process globals are nobody's, every task carries its own data, children are handed their world at spawn, and the guards turn each classic mistake into a lesson — os.chdir errors, environment writes scope with a note, a bare input() names the spellings that work. Nothing blocks, so nothing deadlocks.

The declared regime is for the tasks that genuinely need a real shared thing — and it is one ladder, each rung claiming strictly more than the one below it:

lanes=(db,) — owns exactly the named resources; contends only with other claimants of the same lanes, everything unrelated runs beside it. (cwd_lane roots the real directory at the task's cwd for the hold; console_lane is the terminal, which interactive=True spells for you.)
serial=True — owns the process globals: the all-lanes claim, said in one word. At most one at a time, overlapping the parallel pool; real chdir legal inside.
exclusive=True — owns the machine; nothing else in flight.

Every rung is granted at task boundaries by the scheduler, all at once, which is why claims can be scheduled instead of contended for — the deadlocks page is why that distinction earns its keep.

The sentence to defend¶

In a parallel run, the only non-parallel execution is the kind you declared. Everything else runs at full width; the worst degradation anywhere else is speed, never parallelism — and every remaining wait says its name.

From here, the Working directory & environment guide page shows the product surface, and the Cookbook has the worked recipes.