apple_kit

RadrootsTransferCallbackQueue.swift (1409B)

---

 import Foundation
 
 /// Delegate callbacks arrive on a serial OS queue. Preserve that order across
 /// Swift suspension so finished events cannot overtake receipt persistence.
 final class RadrootsTransferCallbackQueue: @unchecked Sendable {
     private let lock = NSLock()
     private var tail: Task<Void, Never>?
     private var receipts: [RadrootsBackgroundTransferIdentifier: Int] = [:]
 
     var pendingIdentifiers: Set<RadrootsBackgroundTransferIdentifier> {
         lock.withLock { Set(receipts.keys) }
     }
 
     func enqueue(
         receipt identifier: RadrootsBackgroundTransferIdentifier? = nil,
         operation: @escaping @Sendable () async -> Void
     ) {
         lock.withLock {
             if let identifier {
                 receipts[identifier, default: 0] += 1
             }
             let previous = tail
             tail = Task {
                 await previous?.value
                 await operation()
                 if let identifier {
                     self.finished(identifier)
                 }
             }
         }
     }
 
     private func finished(_ identifier: RadrootsBackgroundTransferIdentifier) {
         lock.withLock {
             let remaining = (receipts[identifier] ?? 1) - 1
             if remaining == 0 {
                 receipts.removeValue(forKey: identifier)
             } else {
                 receipts[identifier] = remaining
             }
         }
     }
 }