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Fix retain cycles #101

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Fix retain cycles #101

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17 changes: 11 additions & 6 deletions Diffusion/Common/Downloader.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -38,28 +38,33 @@ class Downloader: NSObject, ObservableObject {
#endif
urlSession = URLSession(configuration: config, delegate: self, delegateQueue: OperationQueue())
downloadState.value = .downloading(0)
urlSession?.getAllTasks { tasks in
// If there's an existing pending background task with the same URL, let it proceed.
urlSession?.getAllTasks { [weak self] tasks in
// Avoiding retain cycles by capturing weak self in stead of self.
guard let weakSelf = self else { return }
guard tasks.filter({ $0.originalRequest?.url == url }).isEmpty else {
print("Already downloading \(url)")
return
}
print("Starting download of \(url)")

var request = URLRequest(url: url)
if let authToken = authToken {
request.setValue("Bearer \(authToken)", forHTTPHeaderField: "Authorization")
}

self.urlSession?.downloadTask(with: request).resume()
// if we used strong self, retain cycles may occur, especially in async network calls.
// To avoid that, we should use weak self.
weakSelf.urlSession?.downloadTask(with: request).resume()
}

}

@discardableResult
func waitUntilDone() throws -> URL {
// It's either this, or stream the bytes ourselves (add to a buffer, save to disk, etc; boring and finicky)
let semaphore = DispatchSemaphore(value: 0)
stateSubscriber = downloadState.sink { state in
stateSubscriber = downloadState.sink { [weak self] state in
// Without [weak self], this could create a retain cycle, especially since sink maintains a strong reference to self for the duration of the subscription.
guard let weakSelf = self else { return }
switch state {
case .completed: semaphore.signal()
case .failed: semaphore.signal()
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