Add a mutex_map example

Fixes #128

Author: Paul Kernfeld

examples/mutex_map.rs

@@ -0,0 +1,23 @@
+//! This example shows how to wrap a data structure in a mutex to achieve safe mutability.
+extern crate lazy_static;
+use lazy_static::lazy_static;
+use std::collections::HashMap;
+use std::sync::Mutex;
+
+lazy_static! {
+    static ref MUTEX_MAP: Mutex<HashMap<u32, &'static str>> = {
+        let mut m = HashMap::new();
+        m.insert(0, "foo");
+        m.insert(1, "bar");
+        m.insert(2, "baz");
+        Mutex::new(m)
+    };
+}
+
+fn main() {
+    MUTEX_MAP.lock().unwrap().insert(0, "boo");
+    println!(
+        "The entry for `0` is \"{}\".",
+        MUTEX_MAP.lock().unwrap().get(&0).unwrap()
+    );
+}