Selective Download Cancellation #84
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Wraps each download in its own asyncio.Task and tracks download_id to Task mapping in _active_download_tasks. This enables cancelling specific downloads without stopping the entire worker. Shutdown now cancels active downloads when wait_for_current=False.
Adds _cancelled_ids set to pool. When worker dequeues an item, checks if the download_id is in the cancelled set. If so, emits download.cancelled event with cancelled_from=QUEUED and skips processing. This enables cancelling downloads that haven't started yet.
Implements cancel(download_id) -> bool on WorkerPool: - For in-progress downloads: cancels the task directly - For queued downloads: adds to _cancelled_ids for cooperative cancellation - Returns False for unknown IDs (manager will check tracker for terminal state)
Implements cancel(download_id) -> CancelResult on DownloadManager: - Delegates to pool for active/queued downloads - Uses tracker to distinguish ALREADY_TERMINAL vs NOT_FOUND - Workers continue processing remaining queue items after cancellation
Add comprehensive integration tests for selective download cancellation: - TestCancelInProgress: verify partial file cleanup, tracker status, events - TestCancelQueued: verify queued downloads skipped, correct event state - TestCancelAndContinue: verify workers continue after cancellation - TestCancelAlreadyTerminal: verify ALREADY_TERMINAL for completed downloads - TestCancelEventSubscription: verify external subscribers receive events Uses slow_response callback to control timing for reliable queue state testing.
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Move task creation, tracking, and cancellation handling logic from _process_queue into dedicated helper method. Improves readability and separates concerns for download task lifecycle management.
- Add cancellation to feature lists in READMEs - Add Selective Cancellation section with API example - Document CancelResult and CancelledFrom enums in architecture - Add Cancellation Flow to architecture data flows - Update roadmap to mark feature as done
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Summary
Implements the cancellation mechanism for selective download cancellation, allowing users to cancel individual downloads by ID.
Changes
Pool-level cancellation (
WorkerPool)_active_download_tasksdict to track in-progress download tasks_cancelled_idsset for cooperative cancellation of queued downloads_handle_cancelled_queued()to skip cancelled items when dequeuedcancel(download_id) -> boolmethod to cancel active or queued downloadsManager-level API (
DownloadManager)cancel(download_id) -> CancelResultpublic methodCANCELLED,ALREADY_TERMINAL, orNOT_FOUNDbased on stateTests
API
result = await manager.cancel(download_id)
Returns: CancelResult.CANCELLED | CancelResult.ALREADY_TERMINAL | CancelResult.NOT_FOUND