book: Add example that reqwest fails without tokio

book/listings/Cargo.toml

@@ -220,6 +220,9 @@ path = "main_event_loop/7/main.rs"
 name = "main_event_loop_8"
 path = "main_event_loop/8/main.rs"
 
+[[bin]]
+name = "main_event_loop_9"
+path = "main_event_loop/9/main.rs"
 
 # saving_window_state
 [[bin]]

book/listings/main_event_loop/8/main.rs

@@ -2,13 +2,8 @@ use glib::{clone, MainContext, Priority};
 use gtk::glib;
 use gtk::prelude::*;
 use gtk::{Application, ApplicationWindow, Button};
-use once_cell::sync::Lazy;
-use tokio::runtime::Runtime;
 
-// ANCHOR: tokio_runtime
 const APP_ID: &str = "org.gtk_rs.MainEventLoop8";
-static RUNTIME: Lazy<Runtime> =
-    Lazy::new(|| Runtime::new().expect("Setting up tokio runtime needs to succeed."));
 
 fn main() -> glib::ExitCode {
     // Create a new application
@@ -20,7 +15,6 @@ fn main() -> glib::ExitCode {
     // Run the application
     app.run()
 }
-// ANCHOR_END: tokio_runtime
 
 fn build_ui(app: &Application) {
     // Create a button
@@ -36,7 +30,9 @@ fn build_ui(app: &Application) {
     let (sender, receiver) = MainContext::channel(Priority::default());
     // Connect to "clicked" signal of `button`
     button.connect_clicked(move |_| {
-        RUNTIME.spawn(clone!(@strong sender => async move {
+        let main_context = MainContext::default();
+        // The main loop executes the asynchronous block
+        main_context.spawn_local(clone!(@strong sender => async move {
             let response = reqwest::get("https://www.gtk-rs.org").await;
             sender
                 .send(response)
@@ -49,7 +45,7 @@ fn build_ui(app: &Application) {
         if let Ok(response) = response {
             println!("Status {}", response.status());
         } else {
-            println!("Couldn't make a `GET` request.");
+            println!("Could not make a `GET` request.");
         }
         glib::ControlFlow::Continue
     });

book/listings/main_event_loop/9/main.rs

@@ -0,0 +1,67 @@
+use glib::{clone, MainContext, Priority};
+use gtk::glib;
+use gtk::prelude::*;
+use gtk::{Application, ApplicationWindow, Button};
+use once_cell::sync::Lazy;
+use tokio::runtime::Runtime;
+
+// ANCHOR: tokio_runtime
+const APP_ID: &str = "org.gtk_rs.MainEventLoop8";
+static RUNTIME: Lazy<Runtime> =
+    Lazy::new(|| Runtime::new().expect("Setting up tokio runtime needs to succeed."));
+
+fn main() -> glib::ExitCode {
+    // Create a new application
+    let app = Application::builder().application_id(APP_ID).build();
+
+    // Connect to "activate" signal of `app`
+    app.connect_activate(build_ui);
+
+    // Run the application
+    app.run()
+}
+// ANCHOR_END: tokio_runtime
+
+fn build_ui(app: &Application) {
+    // Create a button
+    let button = Button::builder()
+        .label("Press me!")
+        .margin_top(12)
+        .margin_bottom(12)
+        .margin_start(12)
+        .margin_end(12)
+        .build();
+
+    // ANCHOR: callback
+    let (sender, receiver) = MainContext::channel(Priority::default());
+    // Connect to "clicked" signal of `button`
+    button.connect_clicked(move |_| {
+        RUNTIME.spawn(clone!(@strong sender => async move {
+            let response = reqwest::get("https://www.gtk-rs.org").await;
+            sender
+                .send(response)
+                .expect("Could not send through channel");
+        }));
+    });
+
+    // The main loop executes the closure as soon as it receives the message
+    receiver.attach(None, move |response| {
+        if let Ok(response) = response {
+            println!("Status {}", response.status());
+        } else {
+            println!("Could not make a `GET` request.");
+        }
+        glib::ControlFlow::Continue
+    });
+    // ANCHOR_END: callback
+
+    // Create a window
+    let window = ApplicationWindow::builder()
+        .application(app)
+        .title("My GTK App")
+        .child(&button)
+        .build();
+
+    // Present window
+    window.present();
+}

book/src/main_event_loop.md

@@ -212,20 +212,30 @@ If you decide to share it, you user name will be printed on the console.
 
 
 ```
-cargo add tokio@1 --features rt-multi-thread
 cargo add [email protected] --features rustls-tls --no-default-features
 ```
 
 Filename: <a class=file-link href="https://github.com/gtk-rs/gtk4-rs/blob/master/book/listings/main_event_loop/8/main.rs">listings/main_event_loop/8/main.rs</a>
 
 ```rust
-{{#rustdoc_include ../listings/main_event_loop/8/main.rs:tokio_runtime}}
+{{#rustdoc_include ../listings/main_event_loop/8/main.rs:callback}}
+```
+
+```
+cargo add tokio@1 --features rt-multi-thread
 ```
 
-Filename: <a class=file-link href="https://github.com/gtk-rs/gtk4-rs/blob/master/book/listings/main_event_loop/8/main.rs">listings/main_event_loop/8/main.rs</a>
+
+Filename: <a class=file-link href="https://github.com/gtk-rs/gtk4-rs/blob/master/book/listings/main_event_loop/9/main.rs">listings/main_event_loop/9/main.rs</a>
 
 ```rust
-{{#rustdoc_include ../listings/main_event_loop/8/main.rs:callback}}
+{{#rustdoc_include ../listings/main_event_loop/9/main.rs:tokio_runtime}}
+```
+
+Filename: <a class=file-link href="https://github.com/gtk-rs/gtk4-rs/blob/master/book/listings/main_event_loop/9/main.rs">listings/main_event_loop/9/main.rs</a>
+
+```rust
+{{#rustdoc_include ../listings/main_event_loop/9/main.rs:callback}}
 ```