# Paths and Locking

**The absolute-POSIX path helpers the sessions use, and the lock they take over the path map.**

```ts
import {
  basename,
  dirname,
  isPathInside,
  joinPath,
  normalizePath,
  PathLock,
  splitPath,
} from "mountx";
```

Both are exported because a driver doing its own path bookkeeping wants the same rules the transports follow — not because a driver has to call them. Every path a driver receives is already normalized.

## Path helpers

Absolute POSIX paths only; `..` clamps at the root, so no input can escape upward out of the mount.

```ts
splitPath("/a/b"); // ["a", "b"]
normalizePath("/a//b/../c"); // "/a/c"
joinPath("/a", "b"); // "/a/b"
dirname("/a/b"); // "/a"
basename("/a/b"); // "b"
isPathInside("/a/b", "/a"); // true
```

## `PathLock`

The writer lock over the path map, shared by both transports' sessions. `RENAME` takes it; `READ`/`WRITE` run outside it — the whole point being that bulk I/O never waits on a rename that is not in its way.

## Next

- [Driver interface](/reference/driver-interface) — where those paths arrive.
- [Tuning](/guide/tuning) — concurrency, and what the lock costs.