Random 502 cgi gateway error when response 304 then flush response

[303248153]

First I found this problem with my project, sometime static files will return 502 with cgi gateway error.
Today I do a diggup, to reproduce this problem you needs:

• Host asp.net core application on IIS, if you run with kestrel only, this problem won't happen.
• Response 304, only 304 cause this problem.
• Explict flush the response
• Do the request parallel

I uploaded a minimal reproduce project, please check it.
It maybe a thread race condition problem because only parallel request will cause this problem.
WebApplication1.zip

I don't known if it's same with other 502.3 issues,
and I already using asp.net core 1.0.0 as you can see in the project.json.

[Tratcher]

This seems to be a Kestrel issue. Updated repro code:

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole();

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.Run(ThreadPoolVersion);
        }

        private async Task DefaultVersion(HttpContext context)
        {
            if (context.Request.Path == "/")
            {
                context.Response.ContentType = "text/html";
                var html = string.Join("",
                    Enumerable.Range(0, 100).Select(n => $"<img src='/{n}.jpg'></img>"));
                await context.Response.WriteAsync(html);
            }
            else if (context.Request.Path.Value.EndsWith(".jpg"))
            {
                context.Response.Headers.Add("Last-Modified", "Fri, 17 Jun 2016 06:56:44 GMT");
                context.Response.ContentType = "image/jpeg";
                context.Response.StatusCode = 304;
                await context.Response.Body.FlushAsync();
                // context.Response.Body.Flush();
            }
        }

I saw the same behaviors with both the DefaultVersion and ThreadPoolVersion repro methods. If I start the site with just Kestrel then the browser will make many parallel requests but only the first 8 will complete, the remainder time out. If I launch IIS Express then most of the requests complete, but 1/10 fail with a 502.

[Tratcher]

This issue was moved to aspnet/KestrelHttpServer#952