My experience recently playing around with our locking behaviour is
that, while mostly seamless and not seen by users, it's leaks
implementation details a bit too heavily.
As a result, the following improvements are in this commit:
- Ensure that, whenever possible, we tell the user the actual command
that is holding a given lock instead of the lock name (an internal
implementation detail)
- Make the locking error output a little more consistent and user
friendly
- Add a `DownloadLock` class to simplify locking downloads
- Add a `HOMEBREW_LOCK_CONTEXT` variable to allow adding additional
context for logging error messages
- Lock paths and leave deciding how this translates to lock names up
to the locking code itself
- Lock the Cellar/Caskroom paths explicitly rather than implicitly
Co-authored-by: Carlo Cabrera <30379873+carlocab@users.noreply.github.com>
Consolidate the handling of which directories need to exist and which
need to be writable. Additionally, add a fatal check for formula
installations to ensure that any directories that need to be writable
are so before attempting an installation.
Fixes#4626.
