Pasted

+extern crate futures;
+extern crate futures_cpupool;
+extern crate void;
+
+use std::borrow::Borrow;
 use std::collections::HashMap;
-use std::sync::{Arc,RwLock};
-use std::thread;
+use std::sync::{Arc, RwLock};
 
-fn poll_for(mapping: Arc<RwLock<HashMap<i32, Arc<RwLock<i32>>>>>, key: i32) -> Arc<RwLock<i32>> {
-    loop {
-        match mapping.read().unwrap().get(&key) {
-            Some(i) => return i.clone(),
-            None => ()
-        }
+use futures::future::{BoxFuture, Future, lazy, ok, Shared, SharedItem, SharedError};
+
+type MyShared = Shared<Future<Item=i32, Error=void::Void>>;
+
+struct CachingMap(Arc<RwLock<HashMap<i32, MyShared>>>);
+
+impl Clone for CachingMap {
+    fn clone(&self) -> CachingMap {
+        CachingMap(self.0.clone())
     }
 }
 
-fn q(mapping: Arc<RwLock<HashMap<i32, Arc<RwLock<i32>>>>>, key: i32) -> i32 {
-    println!("Running for {:?}", key);
-    {
-        match mapping.read().unwrap().get(&key) {
-            Some(i) => return *i.read().unwrap(),
-            None => ()
+impl CachingMap {
+    fn new() -> CachingMap {
+        CachingMap(Arc::new(RwLock::new(HashMap::new())))
+    }
+
+    fn q_basis() -> CachingMap {
+        let caching_map = CachingMap::new();
+        let clone = caching_map.0.clone();
+        let mut mapping = clone.write().unwrap();
+        mapping.insert(1, ok(1).shared());
+        mapping.insert(2, ok(1).shared());
+        caching_map
+    }
+
+    fn q(&self, key: i32) -> MyShared {
+        {
+            match self.0.read().unwrap().get(&key) {
+                Some(value) => return value.clone(),
+                None => (),
+            }
         }
-    }
-    {
-        println!("Generating for {:?}", key);
-        let lock = Arc::new(RwLock::new(0));
-        let mut val = lock.write().unwrap();
+
         {
             use std::collections::hash_map::Entry::*;
-            let mut mutable_mapping = mapping.write().unwrap();
-            match mutable_mapping.entry(key) {
-                Occupied(entry) => return *entry.get().read().unwrap(),
-                Vacant(entry) => {entry.insert(lock.clone());}
+            let mut mapping = self.0.write().unwrap();
+            match mapping.entry(key) {
+                Occupied(entry) => entry.get(),
+                Vacant(entry) => entry.insert(self.calculate_q(key))
             }
-            println!("Inserted for {:?}", key);
         }
-        {
-            let _mapping = mapping.clone();
-            thread::spawn(move || {
-                q(_mapping, key - 1);
-            });
-        }
-        {
-            let prev = poll_for(mapping.clone(), key - 1);
-            let prev_prev = poll_for(mapping.clone(), key - 2);
-            let first = poll_for(mapping.clone(), key - *prev.read().unwrap());
-            let second = poll_for(mapping.clone(), key - *prev_prev.read().unwrap());
-            *val = *first.read().unwrap() + *second.read().unwrap();
-        }
-        *val
+    }
+
+    fn calculate_q(&self, key: i32) -> MyShared {
+        let prev = lazy(|| self.q(key - 1));
+        let prev_prev = lazy(|| self.q(key - 2));
+        let first = prev.map(|q| self.q(key - q.unwrap()).wait());
+        let second = prev_prev.map(|q| self.q(key - q.unwrap()).wait());
+        first.join(second).map(|(first, second)| first.unwrap() + second.unwrap()).shared()
     }
 }
 
 fn main() {
-    let mut mapping = HashMap::new();
-    mapping.insert(1, Arc::new(RwLock::new(1)));
-    mapping.insert(2, Arc::new(RwLock::new(1)));
-    let mapping = Arc::new(RwLock::new(mapping));
-    println!("{:?}", q(mapping.clone(), 10));
-    println!("{:?}", q(mapping.clone(), 10));
+    let cache = CachingMap::q_basis();
+    //println!("{:?}", cache.q(10));
+    //println!("{:?}", cache.q(10));
 }