node: AssemblyLoadContext.Default.Unloading might not be reliable for thorough disposition

[Qiao-Jin]

In these lines we set up Unloading events which are executed when user closes neo-cli.

neo-node/Neo.ConsoleService/ConsoleServiceBase.cs

Lines 273 to 279 in 7aa1e16

	public virtual void OnStart(string[] args)
	{
	// Register sigterm event handler
	AssemblyLoadContext.Default.Unloading += SigTermEventHandler;
	// Register sigint event handler
	Console.CancelKeyPress += CancelHandler;
	}

However there might be problems in this strategy. Unless user chooses to close cli by typing "exit" command, other ways such as directly clicking "close" button will leave only no more than 2 seconds for this event. That means, if disposition actions take longer than this time period, whole process will be shut down before everything disposed gracefully.

Currently there seems nothing that must be disposed before shutting down (even DB), but still this is some vulnerability easy to be neglected.

https://docs.microsoft.com/en-us/dotnet/api/system.appdomain.processexit?f1url=https%3A%2F%2Fmsdn.microsoft.com%2Fquery%2Fdev15.query%3FappId%3DDev15IDEF1%26l%3DEN-US%26k%3Dk(System.AppDomain.ProcessExit)%3Bk(SolutionItemsProject)%3Bk(SolutionItemsProject)%3Bk(SolutionItemsProject)%3Bk(DevLang-csharp)%26rd%3Dtrue&view=net-5.0

[shargon]

Old, if remains, please re-open