Add a poll() method on futures

.gitignore

@@ -1,2 +1,3 @@
 target/
 **/*.rs.bk
+build/

src/player.rs

@@ -11,8 +11,8 @@ py_class!(pub class Player |py| {
         let track = *track.id(py);
 
         let end_of_track = player.load(track, play, position_ms);
-        PyFuture::new(py, end_of_track, |py, _result| {
-            Ok(py.None())
+        PyFuture::new(py, end_of_track, |_py, _result| {
+            Ok(true)
         })
     }
 

src/pyfuture.rs

@@ -1,23 +1,62 @@
-use futures::Future;
-use std::cell::RefCell;
 use cpython::{PyResult, PyObject, Python, PythonObject, ToPyObject};
+use futures::executor;
+use futures::{Future, Async};
+use std::cell::RefCell;
+use std::sync::Arc;
 
-// Workaround rust-lang/rust#28796
 pub trait Callback : Send {
-    fn call(self: Box<Self>, py: Python) -> PyResult<PyObject>;
+    fn poll(&mut self, py: Python) -> PyResult<Option<PyObject>>;
+    fn wait(&mut self, py: Python) -> PyResult<PyObject>;
+}
+
+struct FutureData<F, T> {
+    future: Option<executor::Spawn<F>>,
+    then: Option<T>,
 }
-impl <F: Send + for<'a> FnOnce(Python<'a>) -> PyResult<PyObject>> Callback for F {
-    fn call(self: Box<Self>, py: Python) -> PyResult<PyObject> {
-        (*self)(py)
+
+struct NoopUnpark;
+impl executor::Unpark for NoopUnpark {
+    fn unpark(&self) {}
+}
+
+impl <F, T, U> Callback for FutureData<F, T>
+    where F: Future + Send + 'static,
+          T: FnOnce(Python, Result<F::Item, F::Error>) -> PyResult<U> + Send + 'static,
+          U: ToPyObject
+{
+    fn poll(&mut self, py: Python) -> PyResult<Option<PyObject>> {
+        let result = {
+            let future = self.future.as_mut().expect("Future already completed");
+            match future.poll_future(Arc::new(NoopUnpark)) {
+                Ok(Async::Ready(v)) => Ok(v),
+                Err(e) => Err(e),
+                Ok(Async::NotReady) => return Ok(None),
+            }
+        };
+
+        self.future = None;
+        let then = self.then.take().unwrap();
+        then(py, result).map(|o| Some(o.into_py_object(py).into_object()))
+    }
+
+    fn wait(&mut self, py: Python) -> PyResult<PyObject> {
+        let mut future = self.future.take().expect("Future already completed");
+        let result = future.wait_future();
+
+        let then = self.then.take().unwrap();
+        then(py, result).map(|o| o.into_py_object(py).into_object())
     }
 }
 
 py_class!(pub class PyFuture |py| {
-    data callback : RefCell<Option<Box<Callback>>>;
+    data callback : RefCell<Box<Callback>>;
+
+    def poll(&self) -> PyResult<Option<PyObject>> {
+        self.callback(py).borrow_mut().poll(py)
+    }
 
     def wait(&self) -> PyResult<PyObject> {
-        let callback = self.callback(py).borrow_mut().take().expect("Future already completed");
-        callback.call(py)
+        self.callback(py).borrow_mut().wait(py)
     }
 });
 
@@ -27,10 +66,10 @@ impl PyFuture {
               T: FnOnce(Python, Result<F::Item, F::Error>) -> PyResult<U> + Send + 'static,
               U: ToPyObject
     {
-        PyFuture::create_instance(py, RefCell::new(Some(Box::new(move |py: Python| {
-            let result = future.wait();
-            then(py, result).map(|o| o.into_py_object(py).into_object())
-        }))))
+        PyFuture::create_instance(py, RefCell::new(Box::new(FutureData {
+            future: Some(executor::spawn(future)),
+            then: Some(then),
+        })))
     }
 }