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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,108 @@ | ||
| import UIKit | ||
| import Collections | ||
|
|
||
| @ImageDownloaderActor | ||
| public final class ImagePrefetcher { | ||
| private let downloader: ImageDownloader | ||
| private let maxConcurrentTasks: Int | ||
| private var queue = OrderedDictionary<PrefetchKey, PrefetchTask>() | ||
| private var numberOfActiveTasks = 0 | ||
|
|
||
| deinit { | ||
| let tasks = queue.values.compactMap(\.task) | ||
| for task in tasks { | ||
| task.cancel() | ||
| } | ||
| } | ||
|
|
||
| public nonisolated init(downloader: ImageDownloader, maxConcurrentTasks: Int = 2) { | ||
| self.downloader = downloader | ||
| self.maxConcurrentTasks = maxConcurrentTasks | ||
| } | ||
|
|
||
| public nonisolated func startPrefetching(for requests: [ImageRequest]) { | ||
| Task { @ImageDownloaderActor in | ||
| for request in requests { | ||
| startPrefetching(for: request) | ||
| } | ||
| performPendingTasks() | ||
| } | ||
| } | ||
|
|
||
| private func startPrefetching(for request: ImageRequest) { | ||
| let key = PrefetchKey(request: request) | ||
| guard queue[key] == nil else { | ||
| return | ||
| } | ||
| queue[key] = PrefetchTask() | ||
| } | ||
|
|
||
| private func performPendingTasks() { | ||
| var index = 0 | ||
| func nextPendingTask() -> (PrefetchKey, PrefetchTask)? { | ||
| while index < queue.count { | ||
| if queue.elements[index].value.task == nil { | ||
| return queue.elements[index] | ||
| } | ||
| index += 1 | ||
| } | ||
| return nil | ||
| } | ||
| while numberOfActiveTasks < maxConcurrentTasks, let (key, task) = nextPendingTask() { | ||
| task.task = Task { | ||
| await self.actuallyPrefetchImage(for: key.request) | ||
| } | ||
| numberOfActiveTasks += 1 | ||
| } | ||
| } | ||
|
|
||
| private func actuallyPrefetchImage(for request: ImageRequest) async { | ||
| _ = try? await downloader.image(for: request) | ||
|
|
||
| numberOfActiveTasks -= 1 | ||
| queue[PrefetchKey(request: request)] = nil | ||
| performPendingTasks() | ||
| } | ||
|
|
||
| public nonisolated func stopPrefetching(for requests: [ImageRequest]) { | ||
| Task { @ImageDownloaderActor in | ||
| for request in requests { | ||
| stopPrefetching(for: request) | ||
| } | ||
| performPendingTasks() | ||
| } | ||
| } | ||
|
|
||
| private func stopPrefetching(for request: ImageRequest) { | ||
| let key = PrefetchKey(request: request) | ||
| if let task = queue.removeValue(forKey: key) { | ||
| task.task?.cancel() | ||
| } | ||
| } | ||
|
|
||
| public nonisolated func stopAll() { | ||
| Task { @ImageDownloaderActor in | ||
| for (_, value) in queue { | ||
| value.task?.cancel() | ||
| } | ||
| queue.removeAll() | ||
| } | ||
| } | ||
|
|
||
| private struct PrefetchKey: Hashable, Sendable { | ||
| let request: ImageRequest | ||
|
|
||
| func hash(into hasher: inout Hasher) { | ||
| request.source.url?.hash(into: &hasher) | ||
| } | ||
|
|
||
| static func == (lhs: PrefetchKey, rhs: PrefetchKey) -> Bool { | ||
| let (lhs, rhs) = (lhs.request, rhs.request) | ||
| return (lhs.source.url, lhs.options) == (rhs.source.url, rhs.options) | ||
| } | ||
| } | ||
|
|
||
| private final class PrefetchTask: @unchecked Sendable { | ||
| var task: Task<Void, Error>? | ||
| } | ||
| } |
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