Tusker/Tusker/MultiThreadDictionary.swift

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//
// MultiThreadDictionary.swift
// Tusker
//
// Created by Shadowfacts on 5/6/20.
// Copyright © 2020 Shadowfacts. All rights reserved.
//
import Foundation
import os
// once we target iOS 16, replace uses of this with OSAllocatedUnfairLock<[Key: Value]>
// to make the lock semantics more clear
@available(iOS, obsoleted: 16.0)
class MultiThreadDictionary<Key: Hashable & Sendable, Value: Sendable> {
private let lock: any Lock<[Key: Value]>
init() {
if #available(iOS 16.0, *) {
self.lock = OSAllocatedUnfairLock(initialState: [:])
} else {
self.lock = UnfairLock(initialState: [:])
}
}
subscript(key: Key) -> Value? {
get {
return lock.withLock { dict in
dict[key]
}
}
set(value) {
_ = lock.withLock { dict in
dict[key] = value
}
}
}
/// If the result of this function is unused, it is preferable to use `removeValueWithoutReturning` as it executes asynchronously and doesn't block the calling thread.
func removeValue(forKey key: Key) -> Value? {
return lock.withLock { dict in
dict.removeValue(forKey: key)
}
}
func contains(key: Key) -> Bool {
return lock.withLock { dict in
dict.keys.contains(key)
}
}
// TODO: this should really be throws/rethrows but the stupid type-erased lock makes that not possible
func withLock<R>(_ body: @Sendable (inout [Key: Value]) throws -> R) rethrows -> R where R: Sendable {
return try lock.withLock { dict in
return try body(&dict)
}
}
}
// TODO: replace this only with OSAllocatedUnfairLock
@available(iOS, obsoleted: 16.0)
fileprivate protocol Lock<State> {
associatedtype State
func withLock<R>(_ body: @Sendable (inout State) throws -> R) rethrows -> R where R: Sendable
}
@available(iOS 16.0, *)
extension OSAllocatedUnfairLock: Lock {
}
// from http://www.russbishop.net/the-law
fileprivate class UnfairLock<State>: Lock {
private var lock: UnsafeMutablePointer<os_unfair_lock>
private var state: State
init(initialState: State) {
self.state = initialState
self.lock = .allocate(capacity: 1)
self.lock.initialize(to: os_unfair_lock())
}
deinit {
self.lock.deinitialize(count: 1)
self.lock.deallocate()
}
func withLock<R>(_ body: (inout State) throws -> R) rethrows -> R where R: Sendable {
os_unfair_lock_lock(lock)
defer { os_unfair_lock_unlock(lock) }
return try body(&state)
}
}