Backport Fix memory leak with OptionsMonitor #868 to .NET Core 2.1

Issue
Currently there is a memory leak in using OptionsMonitor in .NET Core 2.1 and this has been fixed as part of .NET Core 3.0 and above. (#868)

Solution
Given .NET Core 2.1 has LTS support until 21-08-2021, is it possible to backport this fix to .NET Core 2.1

Alternatives considered
There is no alternative other than upgrading to .NET Core 3.1 and we have a lot of dependencies that needs to be considered which is not going to help us to resolve the memory leak issue in a timely fashion.

Did you run into this? If so where?

Yes, we are using .NET Core 2.1 API hosted on Azure and we are seeing the memory leak behavior there.

How did you reproduce the issue? This particular one required multiple host instantiations and disposals. Did you track down what caused the problem in your case?

We had multiple app services hosting this API on Azure and we noticed the memory leak behavior with the the implementation of OptionsMonitor and OnChange event and when I commented invoking the OnChange event the memory leak stopped.

@shantha05

@shantha05 were you disposing the IDisposable returned from OnChange in your scenario and it was still leaking?

Yes, it was also tried and still it was leaking memory

Were you spinning up multiple instances of the host in a single process? The reason I'm asking these questions is because that PR fixes a very specific issue that would be hard to reproduce without doing something atypical.

We had 2 different App Services in 2 resource groups hosted in 2 locations and routing traffic using Traffic Manager so it's 2 different processes

Then I don't see how that specific PR fixes the issue you're describing. Can you show the code snippet of the leak?

This is the code that was commented to stop the memory leak.

productsOptions.OnChange((config) => {
_productSettings = config;
});

where productOptions is IOptionsMonitor productsOptions

How often did you call OnChange? Once per application? Or once per request? Where is the code that stores the result and disposed it

The API is called 'n' number of times as part of the CertificateAuthenticationHandler once per request. Every CertificateAuthenticationHandler registers itself to the OptionsMonitor.OnChange event.

Can you show the registration and disposal code?

    private IDisposable _listener;

    public CertificateAuthenticationHandler(
        IProductRepository repository, 
        IOptionsMonitor<Products> productsOptions,
        IOptionsMonitor<CertAuthenticationOptions> options, 
        ILoggerFactory loggerFactory, 
        UrlEncoder encoder, 
        ISystemClock clock) 
        : base(options, loggerFactory, encoder, clock)
    {
        _repository = repository;
        _productSettings = productsOptions.CurrentValue;
        _listener = productsOptions.OnChange((config) => {
            _productSettings = config;
        });
    }

    ~CertificateAuthenticationHandler() {
        _listener.Dispose();
    }

Why is there a finalizer? Make the CertificateAuthenticationHandler implement IDisposable and call _listener.Dispose in the Dispose method. That should solve your problem.

Even better would be to use IOptionsSnapshot<T> to get the current snapshot of options (assuming this service is scoped or transient). That would resolve the lifetime mismatch going on here.

Thanks David. Let me give that a try

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Backport Fix memory leak with OptionsMonitor #868 to .NET Core 2.1 #3552

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Backport Fix memory leak with OptionsMonitor #868 to .NET Core 2.1 #3552

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davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

davidfowl commented on Sep 22, 2020

shantha05 commented on Sep 22, 2020

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