feat: add shared state button example

examples/README.md

@@ -14,6 +14,8 @@ Before running any examples that interface with external components, read throug
 
 `gpio_status.rs` - Retrieves the mode and logic level for each of the pins on the 26-pin or 40-pin GPIO header, and displays the results in an ASCII table.
 
+`gpio_shared_button_state.rs` - Shares a state with an input interrupt, stops the program until N event changes.
+
 `i2c_ds3231.rs` - Sets and retrieves the time on a Maxim Integrated DS3231 RTC using I2C.
 
 `pwm_blinkled.rs` - Blinks an LED using hardware PWM.

examples/gpio_shared_button_state.rs

@@ -0,0 +1,52 @@
+// gpio_shared_button_state.rs - Stops the program until a certain amount of event input changes via
+// a non-global shared variable (that can be done using OnceCell for example), this requires a Mutex
+// as it goes across threads and Arc to make sure we have the same entry everywhere.
+
+use std::error::Error;
+use std::sync::{Arc, Mutex};
+use std::time::Duration;
+use rppal::gpio::{Gpio, Event, Trigger};
+
+const INPUT_PIN_GPIO: u8 = 27;
+const STOP_AFTER_N_CHANGES: u8 = 5;
+
+// The function we will run upon a Trigger
+fn input_callback(event: Event, my_data: Arc<Mutex<u8>>) {
+    println!("Event: {:?}", event);
+    *my_data.lock().unwrap() += 1;
+}
+
+fn main() -> Result<(), Box<dyn Error>> {
+    // Initialize our data, in this case it's just a number.
+    let shared_state = Arc::new(Mutex::new(0));
+
+    // Configure the input pin.
+    let mut input_pin = Gpio::new()?.get(INPUT_PIN_GPIO)?.into_input_pullup();
+
+    // We need to clone this as set_async_interrupt will move it and cant be used afterward if so
+    let shared_state_hold = shared_state.clone();
+    input_pin.set_async_interrupt(
+        Trigger::FallingEdge,
+        Some(Duration::from_millis(50)),
+        move |event| {
+            // Note: you can also add more parameters here!
+            input_callback(event, shared_state_hold.clone());
+        },
+    )?;
+
+    // We check constantly if we have reached our number of changes.
+    loop {
+        if *shared_state.lock().unwrap() >= STOP_AFTER_N_CHANGES {
+            // Reached it, exiting the program.
+            println!("Reached {STOP_AFTER_N_CHANGES} events, exiting...");
+            break;
+        }
+
+        // Suppose we do some work here that takes a second, the shorter the work takes, the quicker
+        // we will quit upon reaching our condition.
+        println!("Still waiting...");
+        std::thread::sleep(Duration::from_secs(1));
+    }
+
+    Ok(())
+}