`IStore` crashes when `Swarm<T>` shuts down

[riemannulus]

Context

According to a report from TarogStar. IStore seems to crash when stopping the node.

Problem

https://github.com/planetarium/NineChronicles.Headless/blob/c5d2f8dff819c8d737db91fd2a4ae884dfc5df0f/Libplanet.Headless/Hosting/LibplanetNodeService.cs#L306-L318 When stopping NineChronicles.Headless, Swarm<T>.StopAsync() is called here. But

https://github.com/planetarium/libplanet/blob/977a79462cfe47b88606d6ef4e69b989b297a544/Libplanet.Net/Swarm.cs#L187-L204 Swarm<T>._workerCancellationTokenSoruce is not calling cancel when Swarm<T>.StopAsync()

https://github.com/planetarium/libplanet/blob/977a79462cfe47b88606d6ef4e69b989b297a544/Libplanet.Net/Swarm.cs#L168-L178 Instead, call Swarm<T>._workerCancellationTokenSource.Cancel() in Swarm<T>.Dispose()

https://github.com/planetarium/NineChronicles.Headless/blob/c5d2f8dff819c8d737db91fd2a4ae884dfc5df0f/Libplanet.Headless/Hosting/LibplanetNodeService.cs#L641-L650 The problem is, Dispose doesn't exist to terminate an asynchronous worker task. A request to cancel an asynchronous operation, called at Dispose time, does not guarantee that the asynchronous operation has completely terminated. Therefore, at the time of disposing of IStore that is called after that, a problem may occur when the asynchronous operations access the Disposed Store. And this can also cause problems with the DB used by the store's backend.

[stale[bot]]

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