This fixes an arithmetic overflow crash on iOS 17 caused by the fallback
lock.
In iOS 17, Swift Mutexes are not available, so we have a fallback class
for NdbUseLock that does not make use of them. This allows some thread
safety for iOS 17 users, but unfortunately not as much as iOS 18+ users.
This attempts to fix those remaining race conditions and subsequent
crashes by using `NSLock` in the fallback class, which is available on
iOS 17.
Closes: https://github.com/damus-io/damus/issues/3512
Changelog-Fixed: Fixed a crash on iOS 17 that would happen on startup
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
This adds a sync mechanism in Ndb.swift to coordinate certain usage of
nostrdb.c calls and the need to close nostrdb due to app lifecycle
requirements. Furthermore, it fixes the order of operations when
re-opening NostrDB, to avoid race conditions where a query uses an older
Ndb generation.
This sync mechanism allows multiple queries to happen simultaneously
(from the Swift-side), while preventing ndb from simultaneously closing
during such usages. It also does that while keeping the Ndb interface
sync and nonisolated, which keeps the API easy to use from
Swift/SwiftUI and allows for parallel operations to occur.
If Swift Actors were to be used (e.g. creating an NdbActor), the Ndb.swift
interface would change in such a way that it would propagate the need for
several changes throughout the codebase, including loading logic in
some ViewModels. Furthermore, it would likely decrease performance by
forcing Ndb.swift operations to run sequentially when they could run in
parallel.
Changelog-Fixed: Fixed crashes that happened when the app went into background mode
Closes: https://github.com/damus-io/damus/issues/3245
Signed-off-by: Daniel D’Aquino <daniel@daquino.me>
