Tusker/Tusker/MultiThreadDictionary.swift

105 lines
3.2 KiB
Swift

//
// 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: LockHolder<[AnyHashable: Any]>
init() {
self.lock = LockHolder(initialState: [:])
}
subscript(key: Key) -> Value? {
get {
return try! lock.withLock { dict in
dict[key]
} as! Value?
}
set(value) {
_ = try! 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 try! lock.withLock { dict in
dict.removeValue(forKey: key)
} as! Value?
}
func contains(key: Key) -> Bool {
return try! lock.withLock { dict in
dict.keys.contains(key)
} as! Bool
}
// 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]) -> R) -> R where R: Sendable {
return try! lock.withLock { dict in
var downcasted = dict as! [Key: Value]
defer { dict = downcasted }
return body(&downcasted)
} as! R
}
}
// this type erased struct is necessary due to a compiler bug with stored constrained existential types
// see https://github.com/apple/swift/issues/61403
// see #178
fileprivate struct LockHolder<State> {
let withLock: (_ body: @Sendable (inout State) throws -> any Sendable) throws -> any Sendable
init(initialState: State) {
if #available(iOS 16.0, *) {
let lock = OSAllocatedUnfairLock(initialState: initialState)
self.withLock = lock.withLock(_:)
} else {
let lock = UnfairLock(initialState: initialState)
self.withLock = lock.withLock(_:)
}
}
}
// 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)
}
}