prevent wake_by_ref from decreasing refcount. Fixes #22

src/6_future_example.md

@@ -71,9 +71,9 @@ fn block_on<F: Future>(mut future: F) -> F::Output {
     // We poll in a loop, but it's not a busy loop. It will only run when
     // an event occurs, or a thread has a "spurious wakeup" (an unexpected wakeup
     // that can happen for no good reason).
-    let val = loop { 
+    let val = loop {
         match Future::poll(future.as_mut(), &mut cx) {
-        
+
             // when the Future is ready we're finished
             Poll::Ready(val) => break val,
 
@@ -166,10 +166,10 @@ fn mywaker_clone(s: &MyWaker) -> RawWaker {
 // set of functions
 const VTABLE: RawWakerVTable = unsafe {
     RawWakerVTable::new(
-        |s| mywaker_clone(&*(s as *const MyWaker)),     // clone
+        |s| mywaker_clone(&*(s as *const MyWaker)),   // clone
-        |s| mywaker_wake(&*(s as *const MyWaker)),      // wake
+        |s| mywaker_wake(&*(s as *const MyWaker)),    // wake
-        |s| mywaker_wake(*(s as *const &MyWaker)),      // wake by ref
+        |s| (*(s as *const MyWaker)).parker.unpark(), // wake by ref (don't decrease refcount)
-        |s| drop(Arc::from_raw(s as *const MyWaker)),   // decrease refcount
+        |s| drop(Arc::from_raw(s as *const MyWaker)), // decrease refcount
     )
 };
 
@@ -204,7 +204,7 @@ impl Future for Task {
             // If it's ready we set its state to `Finished`
             *r.tasks.get_mut(&self.id).unwrap() = TaskState::Finished;
             Poll::Ready(self.id)
-        
+
         // If it isn't finished we check the map we have stored in our Reactor
         // over id's we have registered and see if it's there
         } else if r.tasks.contains_key(&self.id) {
@@ -347,7 +347,7 @@ impl Reactor {
             handle: None,
             tasks: HashMap::new(),
         })));
-        
+
         // Notice that we'll need to use `weak` reference here. If we don't,
         // our `Reactor` will not get `dropped` when our main thread is finished
         // since we're holding internal references to it.
@@ -409,7 +409,7 @@ impl Reactor {
     }
 
     // Register a new task with the reactor. In this particular example
-    // we panic if a task with the same id get's registered twice 
+    // we panic if a task with the same id get's registered twice
     fn register(&mut self, duration: u64, waker: Waker, id: usize) {
         if self.tasks.insert(id, TaskState::NotReady(waker)).is_some() {
             panic!("Tried to insert a task with id: '{}', twice!", id);
@@ -458,7 +458,7 @@ fn main() {
 
     // Many runtimes create a global `reactor` we pass it as an argument
     let reactor = Reactor::new();
-    
+
     // We create two tasks:
     // - first parameter is the `reactor`
     // - the second is a timeout in seconds
@@ -496,7 +496,7 @@ fn main() {
 #     });
 #     let waker = waker_into_waker(Arc::into_raw(mywaker));
 #     let mut cx = Context::from_waker(&waker);
-# 
+#
 #     // SAFETY: we shadow `future` so it can't be accessed again.
 #     let mut future = unsafe { Pin::new_unchecked(&mut future) };
 #     let val = loop {
@@ -537,7 +537,7 @@ fn main() {
 #     RawWakerVTable::new(
 #         |s| mywaker_clone(&*(s as *const MyWaker)),   // clone
 #         |s| mywaker_wake(&*(s as *const MyWaker)),    // wake
-#         |s| mywaker_wake(*(s as *const &MyWaker)),    // wake by ref
+#         |s| (*(s as *const MyWaker)).thread.unpark(), // wake by ref (don't decrease refcount)
 #         |s| drop(Arc::from_raw(s as *const MyWaker)), // decrease refcount
 #     )
 # };
@@ -584,7 +584,7 @@ fn main() {
 #     handle: Option<JoinHandle<()>>,
 #     tasks: HashMap<usize, TaskState>,
 # }
-# 
+#
 # #[derive(Debug)]
 # enum Event {
 #     Close,
@@ -599,7 +599,7 @@ fn main() {
 #             handle: None,
 #             tasks: HashMap::new(),
 #         })));
-#         
+#
 #         let reactor_clone = Arc::downgrade(&reactor);
 #         let handle = thread::spawn(move || {
 #             let mut handles = vec![];
@@ -624,7 +624,7 @@ fn main() {
 #         reactor.lock().map(|mut r| r.handle = Some(handle)).unwrap();
 #         reactor
 #     }
-# 
+#
 #     fn wake(&mut self, id: usize) {
 #         self.tasks.get_mut(&id).map(|state| {
 #             match mem::replace(state, TaskState::Ready) {
@@ -634,14 +634,14 @@ fn main() {
 #             }
 #         }).unwrap();
 #     }
-# 
+#
 #     fn register(&mut self, duration: u64, waker: Waker, id: usize) {
 #         if self.tasks.insert(id, TaskState::NotReady(waker)).is_some() {
 #             panic!("Tried to insert a task with id: '{}', twice!", id);
 #         }
 #         self.dispatcher.send(Event::Timeout(duration, id)).unwrap();
 #     }
-# 
+#
 #     fn is_ready(&self, id: usize) -> bool {
 #         self.tasks.get(&id).map(|state| match state {
 #             TaskState::Ready => true,
@@ -667,12 +667,12 @@ The last point is relevant when we move on the the last paragraph.
 
 > There is one subtle thing to note about our example. What happens if we pass
 > in the same `id` for both events?
-> 
+>
 > ```rust, ignore
 > let future1 = Task::new(reactor.clone(), 1, 1);
 > let future2 = Task::new(reactor.clone(), 2, 1);
 > ```
-> 
+>
 > We'll discuss this a bit more under exercises in the last chapter where we
 > also look at ways to fix it. For now, just make a note of it so you're aware
 > of the problem.
@@ -796,9 +796,9 @@ fn block_on<F: Future>(mut future: F) -> F::Output {
     let mywaker = Arc::new(MyWaker { parker: parker.clone() }); <--- NB!
     let waker = mywaker_into_waker(Arc::into_raw(mywaker));
     let mut cx = Context::from_waker(&waker);
-    
+
     // SAFETY: we shadow `future` so it can't be accessed again.
-    let mut future = unsafe { Pin::new_unchecked(&mut future) }; 
+    let mut future = unsafe { Pin::new_unchecked(&mut future) };
     loop {
         match Future::poll(future.as_mut(), &mut cx) {
             Poll::Ready(val) => break val,
@@ -822,7 +822,7 @@ fn mywaker_wake(s: &MyWaker) {
 }
 ```
 
-And that's really all there is to it. 
+And that's really all there is to it.
 
 > If you checked out the playground link that showcased how park/unpark could [cause subtle
 > problems](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=b2343661fe3d271c91c6977ab8e681d0)

src/8_finished_example.md

@@ -56,9 +56,9 @@ fn block_on<F: Future>(mut future: F) -> F::Output {
     let mywaker = Arc::new(MyWaker { parker: parker.clone() });
     let waker = mywaker_into_waker(Arc::into_raw(mywaker));
     let mut cx = Context::from_waker(&waker);
-    
+
     // SAFETY: we shadow `future` so it can't be accessed again.
-    let mut future = unsafe { Pin::new_unchecked(&mut future) }; 
+    let mut future = unsafe { Pin::new_unchecked(&mut future) };
     loop {
         match Future::poll(future.as_mut(), &mut cx) {
             Poll::Ready(val) => break val,
@@ -93,7 +93,7 @@ const VTABLE: RawWakerVTable = unsafe {
     RawWakerVTable::new(
         |s| mywaker_clone(&*(s as *const MyWaker)),   // clone
         |s| mywaker_wake(&*(s as *const MyWaker)),    // wake
-        |s| mywaker_wake(*(s as *const &MyWaker)),    // wake by ref
+        |s| (*(s as *const MyWaker)).parker.unpark(), // wake by ref (don't decrease refcount)
         |s| drop(Arc::from_raw(s as *const MyWaker)), // decrease refcount
     )
 };
@@ -151,7 +151,7 @@ impl Reactor {
             handle: None,
             tasks: HashMap::new(),
         })));
-        
+
         let reactor_clone = Arc::downgrade(&reactor);
         let handle = thread::spawn(move || {
             let mut handles = vec![];