X-Git-Url: https://git.ralfj.de/rust-101.git/blobdiff_plain/0223210576f27d0743c2d12b890d30f5c2ef6b2d..2d40516a8393db1f27bb822ff95c71a1a9c82537:/workspace/src/part15.rs

diff --git a/workspace/src/part15.rs b/workspace/src/part15.rs
index 4dca116..148f648 100644
--- a/workspace/src/part15.rs
+++ b/workspace/src/part15.rs
@@ -1,4 +1,75 @@
-// Rust-101, Part 15: Interior Mutability (cont.), RefCell, Cell, Drop
+// Rust-101, Part 15: Mutex, Interior Mutability (cont.), RwLock, Sync
 // ===================================================================
 
+use std::sync::{Arc, Mutex};
+use std::thread;
+use std::time::Duration;
+
+
+// The derived `Clone` implementation will clone the `Arc`, so all clones will actually talk about the same counter.
+#[derive(Clone)]
+struct ConcurrentCounter(Arc<Mutex<usize>>);
+
+impl ConcurrentCounter {
+    // The constructor just wraps the constructors of `Arc` and `Mutex`.
+    pub fn new(val: usize) -> Self {
+        unimplemented!()
+    }
+
+    // The core operation is, of course, `increment`.
+    pub fn increment(&self, by: usize) {
+        // `lock` on a mutex returns a guard, very much like `RefCell`. The guard gives access to the data contained in the mutex.
+        let mut counter = self.0.lock().unwrap();
+        *counter = *counter + by;
+    }
+
+    // The function `get` returns the current value of the counter.
+    pub fn get(&self) -> usize {
+        unimplemented!()
+    }
+}
+
+// Now our counter is ready for action.
+pub fn main() {
+    let counter = ConcurrentCounter::new(0);
+
+    // We clone the counter for the first thread, which increments it by 2 every 15ms.
+    let counter1 = counter.clone();
+    let handle1 = thread::spawn(move || {
+        for _ in 0..10 {
+            thread::sleep(Duration::from_millis(15));
+            counter1.increment(2);
+        }
+    });
+
+    // The second thread increments the counter by 3 every 20ms.
+    let counter2 = counter.clone();
+    let handle2 = thread::spawn(move || {
+        for _ in 0..10 {
+            thread::sleep(Duration::from_millis(20));
+            counter2.increment(3);
+        }
+    });
+
+    // Now we watch the threads working on the counter.
+    for _ in 0..50 {
+        thread::sleep(Duration::from_millis(5));
+        println!("Current value: {}", counter.get());
+    }
+
+    // Finally, we wait for all the threads to finish to be sure we can catch the counter's final value.
+    handle1.join().unwrap();
+    handle2.join().unwrap();
+    println!("Final value: {}", counter.get());
+}
+
+// **Exercise 15.1**: Add an operation `compare_and_inc(&self, test: usize, by: usize)` that increments the counter by
+// `by` *only if* the current value is `test`.
+// 
+// **Exercise 15.2**: Rather than panicking in case the lock is poisoned, we can use `into_inner` on the error to recover
+// the data inside the lock. Change the code above to do that. Try using `unwrap_or_else` for this job.
+
+
+// **Exercise 15.3**:  Change the code above to use `RwLock`, such that multiple calls to `get` can be executed at the same time.
+