Also demonstrate how to pass shared counters via Atomic (#242)

Signed-off-by: Daniel Egger <daniel@eggers-club.de>

state/src/main.rs

@@ -11,15 +11,16 @@
 //! We retrieve our app state within our handlers with a `state: Data<...>` argument.
 //!
 //! By default, `actix-web` runs one `App` per logical cpu core.
-//! When running on <N> cores, we see that the example will increment `counter1` (global state)
-//! each time the endpoint is called, but only appear to increment `counter2` every
-//! Nth time on average (thread-local state). This is because the workload is being shared
-//! equally among cores.
+//! When running on <N> cores, we see that the example will increment `counter1` (global state via
+//! Mutex) and `counter3` (global state via Atomic variable) each time the endpoint is called,
+//! but only appear to increment `counter2` every Nth time on average (thread-local state). This
+//! is because the workload is being shared equally among cores.
 //!
 //! Check [user guide](https://actix.rs/docs/application/#state) for more info.
 
 use std::cell::Cell;
 use std::io;
+use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::Mutex;
 
 use actix_web::{middleware, web, App, HttpRequest, HttpResponse, HttpServer};
@@ -28,6 +29,7 @@ use actix_web::{middleware, web, App, HttpRequest, HttpResponse, HttpServer};
 async fn index(
     counter1: web::Data<Mutex<usize>>,
     counter2: web::Data<Cell<u32>>,
+    counter3: web::Data<AtomicUsize>,
     req: HttpRequest,
 ) -> HttpResponse {
     println!("{:?}", req);
@@ -35,11 +37,13 @@ async fn index(
     // Increment the counters
     *counter1.lock().unwrap() += 1;
     counter2.set(counter2.get() + 1);
+    counter3.fetch_add(1, Ordering::SeqCst);
 
     let body = format!(
-        "global counter: {}, local counter: {}",
+        "global mutex counter: {}, local counter: {}, global atomic counter: {}",
         *counter1.lock().unwrap(),
-        counter2.get()
+        counter2.get(),
+        counter3.load(Ordering::SeqCst),
     );
     HttpResponse::Ok().body(body)
 }
@@ -51,15 +55,16 @@ async fn main() -> io::Result<()> {
 
     // Create some global state prior to building the server
     let counter1 = web::Data::new(Mutex::new(0usize));
+    let counter3 = web::Data::new(AtomicUsize::new(0usize));
 
     // move is necessary to give closure below ownership of counter1
     HttpServer::new(move || {
-
         // Create some thread-local state
         let counter2 = Cell::new(0u32);
 
         App::new()
             .app_data(counter1.clone()) // add shared state
+            .app_data(counter3.clone()) // add shared state
             .data(counter2) // add thread-local state
             // enable logger
             .wrap(middleware::Logger::default())