Refactor TaskStack some more, allow for deferred syncronous tasks

src/util.rs

@@ -1,4 +1,4 @@
-use std::{error, fs, io, path};
+use std::{error, fs, io, path, pin};
 
 use tokio_util::sync::CancellationToken;
 
@@ -12,19 +12,13 @@ pub fn open_file(path: &path::Path) -> io::Result<Option<fs::File>> {
     }
 }
 
-struct Task<E>
-where
-    E: error::Error + Send + 'static,
-{
-    canceller: CancellationToken,
-    handle: tokio::task::JoinHandle<Result<(), E>>,
-}
+type StaticFuture<O> = pin::Pin<Box<dyn futures::Future<Output = O> + Send + 'static>>;
 
 pub struct TaskStack<E>
 where
     E: error::Error + Send + 'static,
 {
-    wait_group: Vec<Task<E>>,
+    wait_group: Vec<StaticFuture<Result<(), E>>>,
 }
 
 impl<E> TaskStack<E>
@@ -37,6 +31,16 @@ where
         }
     }
 
+    /// push adds the given Future to the stack, to be executed once stop is called.
+    pub fn push<Fut>(&mut self, f: Fut)
+    where
+        Fut: futures::Future<Output = Result<(), E>> + Send + 'static,
+    {
+        self.wait_group.push(Box::pin(f))
+    }
+
+    /// push_spawn will spawn the given closure in a tokio task. Once the CancellationToken is
+    /// cancelled the closure is expected to return.
     pub fn push_spawn<F, Fut>(&mut self, mut f: F)
     where
         Fut: futures::Future<Output = Result<(), E>> + Send + 'static,
@@ -44,17 +48,21 @@ where
     {
         let canceller = CancellationToken::new();
         let handle = tokio::spawn(f(canceller.clone()));
-        self.wait_group.push(Task { canceller, handle });
+        self.push(async move {
+            canceller.cancel();
+            handle.await.expect("failed to join task")
+        });
     }
 
+    /// stop will process all operations which have been pushed onto the stack in the reverse order
+    /// they were pushed.
     pub async fn stop(mut self) -> Result<(), E> {
         // reverse wait_group in place, so we stop the most recently added first. Since this method
         // consumes self this is fine.
         self.wait_group.reverse();
 
-        for t in self.wait_group {
-            t.canceller.cancel();
-            if let Err(err) = t.handle.await.expect("task failed") {
+        for fut in self.wait_group {
+            if let Err(err) = fut.await {
                 return Err(err);
             }
         }