The gracefullshutdown from avtc

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Race Condition in Shutdown Process

Due to using 2 variables (stopping and pending requests) there is a race condition (though low chance) between the OnStopping and the Invoke, furthermore I would use MemoryBarrier for both the stopping and pending request variable like in this scratch, these will ensure proper read/write ordering in multiprocessor environments:
` private class GracefullShutdown
{
RequestDelegate upstream;
bool isStopping;
int pendingRequests;

        public GracefullShutdown(RequestDelegate upstream, IApplicationLifetime lifetime)
        {
            this.upstream = upstream;
            lifetime.ApplicationStopping.Register(ApplicationStopping);
        }

        public async Task Invoke(HttpContext context)
        {
            if(isStopping)
            {
                context.Response.StatusCode = 500;
                await context.Response.WriteAsync("Application is stopping");
                return;
            }
            Interlocked.Increment(ref pendingRequests);
            try
            {
                //this ammandmend is for solving the race condition due to using two variables (pendngRequests and isStopping) for shutdown handling
                Interlocked.MemoryBarrier();
                if(isStopping)
                {
                    context.Response.StatusCode = 500;
                    await context.Response.WriteAsync("Application is stopping");
                    return;
                }
                await upstream.Invoke(context);
            }
            finally
            {
                Interlocked.Decrement(ref pendingRequests);
            }
        }

        private void ApplicationStopping()
        {
            isStopping = true;
            Interlocked.MemoryBarrier();
            while (pendingRequests > 0)
            {
                Interlocked.MemoryBarrier();
                Thread.Sleep(1000);
            }
        }
    }

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