split part 11 into two, and explain interior mutability and Cell and RefCell in the...

[rust-101.git] / workspace / src / part15.rs

diff --git a/workspace/src/part15.rs b/workspace/src/part15.rs
index 4dca11615b86b5a6395f19213aca405d3f4308c7..d006b23ae92f220c3c27ba5fc122139a0b64e04d 100644 (file)
--- a/workspace/src/part15.rs
+++ b/workspace/src/part15.rs
@@ -1,4 +1,76 @@
-// Rust-101, Part 15: Interior Mutability (cont.), RefCell, Cell, Drop
-// ===================================================================
+// Rust-101, Part 15: Mutex, Interior Mutability (cont.), Sync
+// ===========================================================
+
+use std::sync::{Arc, Mutex};
+use std::thread;
+
+
+// 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!()
+    }
+
+    pub fn increment(&self, by: usize) {
+        // `lock` on a mutex returns a *guard*, giving 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_ms(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_ms(20);
+            counter2.increment(3);
+        }
+    });
+
+    // Now we watch the threads working on the counter.
+    for _ in 0..50 {
+        thread::sleep_ms(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 14.1**: Besides `Mutex`, there's also [`RwLock`](http://doc.rust-lang.org/stable/std/sync/struct.RwLock.html), which
+// provides two ways of locking: One that grants only read-only access, to any number of concurrent readers, and another one
+// for exclusive write access. (Notice that this is the same pattern we already saw with shared vs. mutable borrows.) Change
+// the code above to use `RwLock`, such that multiple calls to `get` can be executed at the same time.
+// 
+// **Exercise 14.2**: Add an operation `compare_and_inc(&self, test: usize, by: usize)` that increments the counter by
+// `by` *only if* the current value is `test`.
+
+
+// FIXME TODO some old outdated explanation FIXME TODO
+