# BlockchainSync Drives a [`ChainstateManager`](/documentation/BitcoinKernel/ChainstateManager) from a [`BlockSource`](/documentation/BitcoinKernel/BlockSource) toward the source’s tip, emitting typed progress updates as blocks are validated. ``` struct BlockchainSync ``` ## Overview Shape follows Apple’s `CLLocationUpdate.liveUpdates(_:)` pattern — a value-type configuration exposing a typed `AsyncSequence` of progress snapshots. Cancel by breaking the `for await` loop or cancelling the enclosing `Task`; the iterator’s cleanup calls [`interrupt()`](/documentation/BitcoinKernel/Context/interrupt()). ```swift let sync = BlockchainSync(manager: manager, source: source, context: context) for await update in sync.updates() { print("\(update.tip.height)/\(update.remoteTip.height) — \(update.state)") } ``` ### Error delivery Failures arrive as `Update(state: .failed(reason), ...)` final elements; the sequence is non-throwing. Cancellation ends the sequence silently (no final Update — cancel is a clean lifecycle event, not a failure). ### Concurrency The sync loop runs on a background `Task` owned by the sequence iterator. Block processing (`ChainstateManager.processBlock`) runs inline — fast for regtest/signet, slow-but-acceptable for mainnet IBD. UI consumers observe progress either through this sequence or [`progress`](/documentation/BitcoinKernel/BlockchainSync/progress) (a `Foundation.Progress` bound to the same state for `SwiftUI.ProgressView` and `BGContinuedProcessingTask.progress` integration).