[PieceWriter] Fix a threading bug and clean up stale state #629
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This can be safely disposed on a background thread as the underlying stream cannot be in use anywhere else at this point.
alanmcgovern
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Whoops - there was a 'ConfigureAwait(false)' here which caused
improper threaded access to the underlying PieceWriter. The
failure mode was that if there was a torrent with hundreds of
tiny files, multiple threads could be opening/closing streams
at the same time and cause issues due to modifying the underlying
'Streams' dictionary while enumerating it.
i.e.
This exception was originally thrown at this call stack:
System.ThrowHelper.ThrowArgumentOutOfRange_IndexException()
System.Collections.Generic.List<T>.RemoveAt(int)
System.Collections.Generic.List<T>.Remove(T)
MonoTorrent.PieceWriter.DiskWriter.MaybeRemoveOldestStreams() in DiskWriter.cs
MonoTorrent.PieceWriter.DiskWriter.GetOrCreateStreamAsync(MonoTorrent.ITorrentManagerFile, System.IO.FileAccess) in DiskWriter.cs
System.Runtime.CompilerServices.ReusableTaskAwaiter<T>.GetResult()
MonoTorrent.PieceWriter.DiskWriter.ReadAsync(MonoTorrent.ITorrentManagerFile, long, System.Memory<byte>) in DiskWriter.cs
DiskWriter has a dictionary mapping ITorrentFile -> list of open streams. When the final stream has been closed, remove the key from the dictionary.
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Several small improvements to the PieceWriter code.
ITorrentFile.The threading fix in point 1 may help with #627