反应式扩展和 IDisposable 管理

Question

I'm trying to use Async versions of Microsoft.Management.Infrastructure , but I'm having hard time figuring out how to do session management with Reactive Extensions.

Here's some background:

• One can create a CIM session using CimSession.CreateAsync , which returns IObservable
• CimSession.CreateAsync returns a CimAsyncResult<T> , which wraps CimAsyncDelegatedObservable<T>
• CimAsyncDelegatedObservable<T> does not dispose CimSession at any point, and thus one must manually dispose CimSession when it is not needed anymore.
• After getting a handle to CimSession , I'm trying to run a WQL query using QueryInstancesAsync , for example session.QueryInstancesAsync(@"root\\cimv2", "WQL", "SELECT Username FROM Win32_ComputerSystem")

If CimSession returned Task s instead of Observable s, the code would be pretty straightforward:

using var session = CimSession.CreateAsync(".");
var results = session.QueryInstancesAsync(@"root\cimv2", "WQL", "SELECT Username FROM Win32_ComputerSystem");

But as the Async methods are implemented using Observable s, I'm not sure how to translate this to idiomatic usage of Observable s. Sure I could translate my methods to Task s using System.Reactive.Linq.Observable.ForEachAsync , but I'd like to learn how to use Observables properly.

To sum it up, my questions would be:

• Bind lifetime of a CimSession to Observable
• How to make sure CimSession gets disposed, if there are no subscribers? Should I force at least one subscriber, but having factory method?
• How to dispose CimSession observable when results for QueryInstancesAsync arrive?

Answer 1

It's a bit of a whacky interface, but give this a go and let me know if it works:

IObservable<string> query =
    from session in CimSession.CreateAsync(".")
    from x in Observable.Using(
        () => session,
        s => s.QueryInstancesAsync(@"root\cimv2", "WQL", "SELECT Username FROM Win32_ComputerSystem"))
    from y in Observable.Using(
        () => x,
        z => Observable.Return(z.GetCimSessionComputerName()))
    select y;

---

If that works, I'd suggest wrapping it in a separate class:

public static class CimSessionEx
{
    public static IObservable<T> CreateObservable<T>(string computerName, string namespaceName, string queryDialect, string queryExpression, Func<CimInstance, IObservable<T>> factory) =>
        from session in CimSession.CreateAsync(computerName)
        from instance in Observable.Using(() => session, s => s.QueryInstancesAsync(namespaceName, queryDialect, queryExpression))
        from y in Observable.Using(() => instance, factory)
        select y;
}

Then you could use it like this:

IObservable<string> query =
    CimSessionEx.CreateObservable(
        ".",
        @"root\cimv2",
        "WQL",
        "SELECT Username FROM Win32_ComputerSystem",
        i => Observable.Return(i.GetCimSessionComputerName()));