As suggested in
https://github.com/denoland/deno/pull/24355#discussion_r1657875422.
I wasn't able to hide the mutex stuff as much as I'd like (ended up just
adding an escape hatch `inner()` method that locks the inner mutex),
because you can't return references to the inner fields through a mutex.
This is mostly motivated by the frozen lockfile changes
Introduces a `SyncReadAsyncWriteLock` to make it harder to write to the
npm resolution without first waiting async in a queue. For the npm
resolution, reading synchronously is fine, but when updating, someone
should wait async, clone the data, then write the data at the end back.
This functionality was broken. The series of events was:
1. Load the npm resolution from the lockfile.
2. Discover only a subset of the specifiers in the documents.
3. Clear the npm snapshot.
4. Redo npm resolution with the new specifiers (~500ms).
What this now does:
1. Load the npm resolution from the lockfile.
2. Discover only a subset of the specifiers in the documents and take
into account the specifiers from the lockfile.
3. Do not redo resolution (~1ms).
