Support IDisposable for Function Handlers

[Dreamescaper]

Describe the feature

It's the same feature request as #342 - to dispose function handler when Lambda service deletes the execution environment.

It was closed because there was no hook from lambda service at that time. But now there is - Lambda sends SIGTERM to runtime before reclaiming the environment.

Use Case

Any features which requires some cleanup.
Flushing logs and traces, closing DB connections, etc.

Proposed Solution

I have implemented it for my handlers via smth like that:

public abstract class AbstractLambdaHandler : IDisposable
{
    private readonly PosixSignalRegistration sigTermRegistration;

    protected AbstractLambdaHandler()
    {
        // AWS Lambda service sends SIGTERM signal before killing lambda container, but 
        // lambda-dotnet runtime does not handle it yet - https://github.com/aws/aws-lambda-dotnet/issues/342 .
        // Until it is implemented, we use custom signal registration to dispose lambda handler.
        sigTermRegistration = PosixSignalRegistration.Create(PosixSignal.SIGTERM, _ =>
        {
            Logger?.LogDebug("SIGTERM signal received. Disposing Lambda Handler.");
            Dispose();
        });
    }

    public virtual void Dispose()
    {
        sigTermRegistration?.Dispose();
        // Dispose other things.
    }
}

It would be nice to have it provided by the runtime itself though.

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

AWS .NET SDK and/or Package version used

Amazon.Lambda.Core 2.7.1

Targeted .NET Platform

.NET 8

Operating System and version

AmazonLinux

[ashishdhingra]

P326185564

[ashishdhingra]

Opened ticket with Lambda team to get more details about SIGTERM signal.