[docs] Add graceful shutdown example (#329)

README.md

@@ -27,6 +27,7 @@ The name mux stands for "HTTP request multiplexer". Like the standard `http.Serv
 * [Static Files](#static-files)
 * [Registered URLs](#registered-urls)
 * [Walking Routes](#walking-routes)
+* [Graceful Shutdown](#graceful-shutdown)
 * [Full Example](#full-example)
 
 ---
@@ -383,6 +384,69 @@ r.Walk(func(route *mux.Route, router *mux.Router, ancestors []*mux.Route) error
 })
 ```
 
+### Graceful Shutdown
+
+Go 1.8 introduced the ability to [gracefully shutdown](https://golang.org/doc/go1.8#http_shutdown) a `*http.Server`. Here's how to do that alongside `mux`:
+
+```go
+package main
+
+import (
+    "context"
+    "flag"
+    "log"
+    "net/http"
+    "os"
+    "os/signal"
+
+    "github.com/gorilla/mux"
+)
+
+func main() {
+    var wait time.Duration
+    flag.DurationVar(&wait, "graceful-timeout", time.Second * 15, "the duration for which the server gracefully wait for existing connections to finish - e.g. 15s or 1m")
+    flag.Parse()
+
+    r := mux.NewRouter()
+    // Add your routes as needed
+    
+    srv := &http.Server{
+        Addr:         "0.0.0.0:8080",
+        // Good practice to set timeouts to avoid Slowloris attacks.
+        WriteTimeout: time.Second * 15,
+        ReadTimeout:  time.Second * 15,
+        IdleTimeout:  time.Second * 60,
+        Handler: r, // Pass our instance of gorilla/mux in.
+    }
+
+    // Run our server in a goroutine so that it doesn't block.
+    go func() {
+        if err := srv.ListenAndServe(); err != nil {
+            log.Println(err)
+        }
+    }()
+    
+    c := make(chan os.Signal, 1)
+    // We'll accept graceful shutdowns when quit via SIGINT (Ctrl+C)
+    // SIGKILL, SIGQUIT or SIGTERM (Ctrl+/) will not be caught.
+    signal.Notify(c, os.Interrupt)
+
+    // Block until we receive our signal.
+    <-c
+
+    // Create a deadline to wait for.
+    ctx, cancel := context.WithTimeout(ctx, wait)
+    // Doesn't block if no connections, but will otherwise wait
+    // until the timeout deadline.
+    srv.Shutdown(ctx)
+    // Optionally, you could run srv.Shutdown in a goroutine and block on
+    // <-ctx.Done() if your application should wait for other services
+    // to finalize based on context cancellation.
+    log.Println("shutting down")
+    os.Exit(0)
+}
+```
+
 ## Full Example
 
 Here's a complete, runnable example of a small `mux` based server: