process subsequent futures when partially progressing a pool

fixes #1737

Author: SrTobi

futures-executor/src/local_pool.rs

@@ -184,12 +184,20 @@ impl LocalPool {
     /// Though only one task will be completed, progress may be made on multiple tasks.
     pub fn try_run_one(&mut self) -> bool {
         poll_executor(|ctx| {
-            let ret = self.poll_pool_once(ctx);
+            loop {
+                let ret = self.poll_pool_once(ctx);
 
-            // return if we really have executed a future
-            match ret {
-                Poll::Ready(Some(_)) => true,
-                _ => false
+                // return if we have executed a future
+                if let Poll::Ready(Some(_)) = ret {
+                    return true;
+                }
+
+                // if there are no new incoming futures
+                // then there is no feature that can make progress
+                // and we can return without having completed a single future
+                if self.incoming.borrow().is_empty() {
+                    return false;
+                }
             }
         })
     }
@@ -220,17 +228,9 @@ impl LocalPool {
     /// of the pool's run or poll methods. While the function is running, all tasks
     /// in the pool will try to make progress.
     pub fn run_until_stalled(&mut self) {
-        poll_executor(|ctx| {
-            loop {
-                let result = self.poll_pool_once(ctx);
-
-                // if there are no more ready futures exit
-                match result {
-                    Poll::Pending | Poll::Ready(None) => return,
-                    _ => continue
-                }
-            }
-        })
+        poll_executor(|ctx| { 
+            let _ = self.poll_pool(ctx);
+        });
     }
 
     // Make maximal progress on the entire pool of spawned task, returning `Ready`

futures-executor/tests/local_pool.rs

@@ -179,6 +179,29 @@ fn try_run_one_returns_on_no_progress() {
     assert_eq!(cnt.get(), ITER);
 }
 
+#[test]
+fn try_run_one_runs_sub_futures() {
+    let mut pool = LocalPool::new();
+    let mut spawn = pool.spawner();
+    let cnt = Rc::new(Cell::new(0));
+
+    let mut inner_spawner = spawn.clone();
+    let cnt1 = cnt.clone();
+    spawn.spawn_local_obj(Box::pin(poll_fn(move |_| {
+        cnt1.set(cnt1.get() + 1);
+        
+        let cnt2 = cnt1.clone();
+        inner_spawner.spawn_local_obj(Box::pin(lazy(move |_|{
+            cnt2.set(cnt2.get() + 1)
+        })).into()).unwrap();
+
+        Poll::Pending
+    })).into()).unwrap();
+
+    pool.try_run_one();
+    assert_eq!(cnt.get(), 2);
+}
+
 #[test]
 fn run_until_stalled_returns_if_empty() {
     let mut pool = LocalPool::new();
@@ -203,6 +226,29 @@ fn run_until_stalled_returns_multiple_times() {
     assert_eq!(cnt.get(), 2);
 }
 
+#[test]
+fn run_until_stalled_runs_spawned_sub_futures() {
+    let mut pool = LocalPool::new();
+    let mut spawn = pool.spawner();
+    let cnt = Rc::new(Cell::new(0));
+
+    let mut inner_spawner = spawn.clone();
+    let cnt1 = cnt.clone();
+    spawn.spawn_local_obj(Box::pin(poll_fn(move |_| {
+        cnt1.set(cnt1.get() + 1);
+        
+        let cnt2 = cnt1.clone();
+        inner_spawner.spawn_local_obj(Box::pin(lazy(move |_|{
+            cnt2.set(cnt2.get() + 1)
+        })).into()).unwrap();
+
+        Poll::Pending
+    })).into()).unwrap();
+
+    pool.run_until_stalled();
+    assert_eq!(cnt.get(), 2);
+}
+
 #[test]
 fn run_until_stalled_executes_all_ready() {
     const ITER: usize = 200;