Use os_unfair_lock for MultiThreadDictionary instead of DispatchQueue
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@ -24,7 +24,7 @@ class ImageCache {
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private let cache: ImageDataCache
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private let desiredPixelSize: CGSize?
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private var groups = MultiThreadDictionary<URL, RequestGroup>(name: "ImageCache request groups")
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private var groups = MultiThreadDictionary<URL, RequestGroup>()
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private var backgroundQueue = DispatchQueue(label: "ImageCache completion queue", qos: .default)
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@ -96,7 +96,7 @@ class ImageCache {
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if let data = data {
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try? self.cache.set(url.absoluteString, data: data, image: image)
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}
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self.groups.removeValueWithoutReturning(forKey: url)
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_ = self.groups.removeValue(forKey: url)
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}
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groups[url] = group
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return group
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@ -7,52 +7,79 @@
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//
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import Foundation
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import os
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class MultiThreadDictionary<Key: Hashable, Value> {
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private let name: String
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private var dict = [Key: Value]()
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private let queue: DispatchQueue
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// once we target iOS 16, replace uses of this with OSAllocatedUnfairLock<[Key: Value]>
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// to make the lock semantics more clear
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@available(iOS, obsoleted: 16.0)
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class MultiThreadDictionary<Key: Hashable & Sendable, Value: Sendable> {
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private let lock: any Lock<[Key: Value]>
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init(name: String) {
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self.name = name
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self.queue = DispatchQueue(label: "MultiThreadDictionary (\(name)) Coordinator", attributes: .concurrent)
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init() {
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if #available(iOS 16.0, *) {
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self.lock = OSAllocatedUnfairLock(initialState: [:])
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} else {
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self.lock = UnfairLock(initialState: [:])
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}
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}
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subscript(key: Key) -> Value? {
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get {
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var result: Value? = nil
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queue.sync {
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result = dict[key]
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return lock.withLock { dict in
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dict[key]
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}
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return result
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}
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set(value) {
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queue.async(flags: .barrier) {
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self.dict[key] = value
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lock.withLock { dict in
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dict[key] = value
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}
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}
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}
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func removeValueWithoutReturning(forKey key: Key) {
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queue.async(flags: .barrier) {
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self.dict.removeValue(forKey: key)
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}
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}
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/// 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.
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func removeValue(forKey key: Key) -> Value? {
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var value: Value? = nil
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queue.sync(flags: .barrier) {
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value = dict.removeValue(forKey: key)
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return lock.withLock { dict in
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dict.removeValue(forKey: key)
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}
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return value
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}
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func contains(key: Key) -> Bool {
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var value: Bool!
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queue.sync {
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value = dict.keys.contains(key)
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return lock.withLock { dict in
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dict.keys.contains(key)
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}
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return value
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}
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func withLock<R>(_ body: @Sendable (inout [Key: Value]) throws -> R) rethrows -> R where R: Sendable {
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return try lock.withLock(body)
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}
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}
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// TODO: replace this only with OSAllocatedUnfairLock
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@available(iOS, obsoleted: 16.0)
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fileprivate protocol Lock<State> {
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associatedtype State
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func withLock<R>(_ body: @Sendable (inout State) throws -> R) rethrows -> R where R: Sendable
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}
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@available(iOS 16.0, *)
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extension OSAllocatedUnfairLock: Lock {
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}
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// from http://www.russbishop.net/the-law
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fileprivate class UnfairLock<State>: Lock {
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private var lock: UnsafeMutablePointer<os_unfair_lock>
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private var state: State
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init(initialState: State) {
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self.state = initialState
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self.lock = .allocate(capacity: 1)
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self.lock.initialize(to: os_unfair_lock())
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}
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deinit {
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self.lock.deallocate()
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}
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func withLock<R>(_ body: (inout State) throws -> R) rethrows -> R where R: Sendable {
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os_unfair_lock_lock(lock)
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defer { os_unfair_lock_unlock(lock) }
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return try body(&state)
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}
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}
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@ -36,7 +36,7 @@ struct AccountDisplayNameLabel<Account: AccountProtocol>: View {
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let matches = emojiRegex.matches(in: account.displayName, options: [], range: fullRange)
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guard !matches.isEmpty else { return }
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let emojiImages = MultiThreadDictionary<String, Image>(name: "AcccountDisplayNameLabel Emoji Images")
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let emojiImages = MultiThreadDictionary<String, Image>()
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let group = DispatchGroup()
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@ -38,10 +38,7 @@ extension BaseEmojiLabel {
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return
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}
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// not using a MultiThreadDictionary so that cached images can be added immediately
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// without jumping through various queues so that we can use them immediately
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// in building either the final string or the string with placeholders
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var emojiImages: [String: UIImage] = [:]
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let emojiImages = MultiThreadDictionary<String, UIImage>()
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var foundEmojis = false
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let group = DispatchGroup()
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@ -71,12 +68,8 @@ extension BaseEmojiLabel {
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group.leave()
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return
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}
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// sync back to the main thread to add the dictionary
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// todo: using the main thread for this isn't great
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DispatchQueue.main.async {
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emojiImages[emoji.shortcode] = transformedImage
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group.leave()
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}
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emojiImages[emoji.shortcode] = transformedImage
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group.leave()
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}
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if let request = request {
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emojiRequests.append(request)
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@ -92,21 +85,27 @@ extension BaseEmojiLabel {
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func buildStringWithEmojisReplaced(usePlaceholders: Bool) -> NSAttributedString {
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let mutAttrString = NSMutableAttributedString(attributedString: attributedString)
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// replaces the emojis starting from the end of the string as to not alter the indices of preceeding emojis
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for match in matches.reversed() {
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let shortcode = (attributedString.string as NSString).substring(with: match.range(at: 1))
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let attachment: NSTextAttachment
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if let emojiImage = emojiImages[shortcode] {
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attachment = NSTextAttachment(emojiImage: emojiImage, in: self.emojiFont, with: self.emojiTextColor)
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} else if usePlaceholders {
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attachment = NSTextAttachment(emojiPlaceholderIn: self.emojiFont)
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} else {
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continue
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// lock once for the entire loop, rather than lock/unlocking for each iteration to do the lookup
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// OSAllocatedUnfairLock.withLock expects a @Sendable closure, so this warns about captures of non-sendable types (attribute dstrings, text checking results)
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// even though the closures is invoked on the same thread that withLock is called, so it's unclear why it needs to be @Sendable (FB11494878)
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// so, just ignore the warnings
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emojiImages.withLock { emojiImages in
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// replaces the emojis starting from the end of the string as to not alter the indices of preceeding emojis
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for match in matches.reversed() {
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let shortcode = (attributedString.string as NSString).substring(with: match.range(at: 1))
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let attachment: NSTextAttachment
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if let emojiImage = emojiImages[shortcode] {
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attachment = NSTextAttachment(emojiImage: emojiImage, in: self.emojiFont, with: self.emojiTextColor)
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} else if usePlaceholders {
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attachment = NSTextAttachment(emojiPlaceholderIn: self.emojiFont)
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} else {
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continue
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}
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let attachmentStr = NSAttributedString(attachment: attachment)
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mutAttrString.replaceCharacters(in: match.range, with: attachmentStr)
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}
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let attachmentStr = NSAttributedString(attachment: attachment)
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mutAttrString.replaceCharacters(in: match.range, with: attachmentStr)
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}
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return mutAttrString
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