feat(lib): change custom executors to be Fn

Instead of custom executors needing to be `tokio::Executor` or
`tokio::TypedExecutor`, they are now just `Fn`s.

BREAKING CHANGE: Configuring an `executor` for a client or server should
  now pass a closure or function to spawn the future.

Closes #1944

examples/single_threaded.rs

@@ -41,7 +41,9 @@ async fn main() {
     let exec = current_thread::TaskExecutor::current();
 
     let server = Server::bind(&addr)
-        .executor(exec)
+        .executor(move |fut| {
+            exec.clone().spawn_local(Box::pin(fut)).unwrap();
+        })
         .serve(make_service);
 
     println!("Listening on http://{}", addr);

src/client/conn.rs

@@ -458,8 +458,7 @@ impl Builder {
     /// Provide an executor to execute background HTTP2 tasks.
     pub fn executor<E>(&mut self, exec: E) -> &mut Builder
     where
-        for<'a> &'a E: tokio_executor::Executor,
-        E: Send + Sync + 'static,
+        E: Fn(crate::common::exec::BoxFuture) + Send + Sync + 'static,
     {
         self.exec = Exec::Executor(Arc::new(exec));
         self

src/client/mod.rs

@@ -359,10 +359,7 @@ where C: Connect + Clone + Send + Sync + 'static,
                                 drop(delayed_tx);
                             });
 
-                        if let Err(err) = executor.execute(on_idle) {
-                            // This task isn't critical, so just log and ignore.
-                            warn!("error spawning task to insert idle connection: {}", err);
-                        }
+                        executor.execute(on_idle);
                     } else {
                         // There's no body to delay, but the connection isn't
                         // ready yet. Only re-insert when it's ready
@@ -371,10 +368,7 @@ where C: Connect + Clone + Send + Sync + 'static,
                         })
                             .map(|_| ());
 
-                        if let Err(err) = executor.execute(on_idle) {
-                            // This task isn't critical, so just log and ignore.
-                            warn!("error spawning task to insert idle connection: {}", err);
-                        }
+                        executor.execute(on_idle);
                     }
                     res
                 })))
@@ -513,20 +507,13 @@ where C: Connect + Clone + Send + Sync + 'static,
                         .handshake(io)
                         .and_then(move |(tx, conn)| {
                             trace!("handshake complete, spawning background dispatcher task");
-                            let bg = executor.execute(conn.map_err(|e| {
+                            executor.execute(conn.map_err(|e| {
                                 debug!("client connection error: {}", e)
                             }).map(|_| ()));
 
-                            // This task is critical, so an execute error
-                            // should be returned.
-                            if let Err(err) = bg {
-                                warn!("error spawning critical client task: {}", err);
-                                return Either::Left(future::err(err));
-                            }
-
                             // Wait for 'conn' to ready up before we
                             // declare this tx as usable
-                            Either::Right(tx.when_ready())
+                            tx.when_ready()
                         })
                         .map_ok(move |tx| {
                             pool.pooled(connecting, PoolClient {
@@ -1013,8 +1000,7 @@ impl Builder {
     /// Provide an executor to execute background `Connection` tasks.
     pub fn executor<E>(&mut self, exec: E) -> &mut Self
     where
-        for<'a> &'a E: tokio_executor::Executor,
-        E: Send + Sync + 'static,
+        E: Fn(crate::common::exec::BoxFuture) + Send + Sync + 'static,
     {
         self.conn_builder.executor(exec);
         self

src/client/pool.rs

@@ -416,16 +416,11 @@ impl<T: Poolable> PoolInner<T> {
 
         let start = Instant::now() + dur;
 
-        let interval = IdleTask {
+        self.exec.execute(IdleTask {
             interval: Interval::new(start, dur),
             pool: WeakOpt::downgrade(pool_ref),
             pool_drop_notifier: rx,
-        };
-
-        if let Err(err) = self.exec.execute(interval) {
-            // This task isn't critical, so simply log and ignore.
-            warn!("error spawning connection pool idle interval: {}", err);
-        }
+        });
     }
 }
 

src/client/service.rs

@@ -63,7 +63,7 @@ where
                                 if let Err(e) = conn.await {
                                     debug!("connection error: {:?}", e);
                                 }
-                            })?;
+                            });
                             Ok(sr)
                         },
                         Err(e) => Err(e)

src/common/exec.rs

@@ -3,83 +3,41 @@ use std::future::Future;
 use std::pin::Pin;
 use std::sync::Arc;
 
-use tokio_executor::{SpawnError, TypedExecutor};
-
 use crate::body::{Payload, Body};
 use crate::proto::h2::server::H2Stream;
 use crate::server::conn::spawn_all::{NewSvcTask, Watcher};
 use crate::service::HttpService;
 
 pub trait H2Exec<F, B: Payload>: Clone {
-    fn execute_h2stream(&mut self, fut: H2Stream<F, B>) -> crate::Result<()>;
+    fn execute_h2stream(&self, fut: H2Stream<F, B>);
 }
 
 pub trait NewSvcExec<I, N, S: HttpService<Body>, E, W: Watcher<I, S, E>>: Clone {
-    fn execute_new_svc(&mut self, fut: NewSvcTask<I, N, S, E, W>) -> crate::Result<()>;
-}
-
-type BoxFuture = Pin<Box<dyn Future<Output=()> + Send>>;
-
-pub trait SharedExecutor {
-    fn shared_spawn(&self, future: BoxFuture) -> Result<(), SpawnError>;
+    fn execute_new_svc(&self, fut: NewSvcTask<I, N, S, E, W>);
 }
 
-impl<E> SharedExecutor for E
-where
-    for<'a> &'a E: tokio_executor::Executor,
-{
-    fn shared_spawn(mut self: &Self, future: BoxFuture) -> Result<(), SpawnError> {
-        tokio_executor::Executor::spawn(&mut self, future)
-    }
-}
+pub type BoxFuture = Pin<Box<dyn Future<Output=()> + Send>>;
 
 // Either the user provides an executor for background tasks, or we use
 // `tokio::spawn`.
 #[derive(Clone)]
 pub enum Exec {
     Default,
-    Executor(Arc<dyn SharedExecutor + Send + Sync>),
+    Executor(Arc<dyn Fn(BoxFuture) + Send + Sync>),
 }
 
 // ===== impl Exec =====
 
 impl Exec {
-    pub(crate) fn execute<F>(&self, fut: F) -> crate::Result<()>
+    pub(crate) fn execute<F>(&self, fut: F)
     where
         F: Future<Output=()> + Send + 'static,
     {
         match *self {
             Exec::Default => {
                 #[cfg(feature = "tcp")]
                 {
-                    use std::error::Error as StdError;
-
-                    struct TokioSpawnError;
-
-                    impl fmt::Debug for TokioSpawnError {
-                        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                            fmt::Debug::fmt("tokio::spawn failed (is a tokio runtime running this future?)", f)
-                        }
-                    }
-
-                    impl fmt::Display for TokioSpawnError {
-                        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-                            fmt::Display::fmt("tokio::spawn failed (is a tokio runtime running this future?)", f)
-                        }
-                    }
-
-                    impl StdError for TokioSpawnError {
-                        fn description(&self) -> &str {
-                            "tokio::spawn failed"
-                        }
-                    }
-
-                    ::tokio_executor::DefaultExecutor::current()
-                        .spawn(Box::pin(fut))
-                        .map_err(|err| {
-                            warn!("executor error: {:?}", err);
-                            crate::Error::new_execute(TokioSpawnError)
-                        })
+                    tokio::spawn(fut);
                 }
                 #[cfg(not(feature = "tcp"))]
                 {
@@ -88,20 +46,18 @@ impl Exec {
                 }
             },
             Exec::Executor(ref e) => {
-                e.shared_spawn(Box::pin(fut))
-                    .map_err(|err| {
-                        warn!("executor error: {:?}", err);
-                        crate::Error::new_execute("custom executor failed")
-                    })
+                e(Box::pin(fut));
             },
         }
     }
 }
 
 impl fmt::Debug for Exec {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.debug_struct("Exec")
-            .finish()
+        match self {
+            Exec::Default => f.write_str("Exec::Default"),
+            Exec::Executor(..) => f.write_str("Exec::Custom"),
+        }
     }
 }
 
@@ -111,7 +67,7 @@ where
     H2Stream<F, B>: Future<Output = ()> + Send + 'static,
     B: Payload,
 {
-    fn execute_h2stream(&mut self, fut: H2Stream<F, B>) -> crate::Result<()> {
+    fn execute_h2stream(&self, fut: H2Stream<F, B>) {
         self.execute(fut)
     }
 }
@@ -122,7 +78,7 @@ where
     S: HttpService<Body>,
     W: Watcher<I, S, E>,
 {
-    fn execute_new_svc(&mut self, fut: NewSvcTask<I, N, S, E, W>) -> crate::Result<()> {
+    fn execute_new_svc(&self, fut: NewSvcTask<I, N, S, E, W>) {
         self.execute(fut)
     }
 }
@@ -131,34 +87,23 @@ where
 
 impl<E, F, B> H2Exec<F, B> for E
 where
-    E: TypedExecutor<H2Stream<F, B>> + Clone,
+    E: Fn(H2Stream<F, B>) + Clone,
     H2Stream<F, B>: Future<Output=()>,
     B: Payload,
 {
-    fn execute_h2stream(&mut self, fut: H2Stream<F, B>) -> crate::Result<()> {
-        self.spawn(fut)
-            .map_err(|err| {
-                warn!("executor error: {:?}", err);
-                crate::Error::new_execute("custom executor failed")
-            })
+    fn execute_h2stream(&self, fut: H2Stream<F, B>) {
+        self(fut);
     }
 }
 
 impl<I, N, S, E, W> NewSvcExec<I, N, S, E, W> for E
 where
-    E: TypedExecutor<NewSvcTask<I, N, S, E, W>> + Clone,
+    E: Fn(NewSvcTask<I, N, S, E, W>) + Clone,
     NewSvcTask<I, N, S, E, W>: Future<Output=()>,
     S: HttpService<Body>,
     W: Watcher<I, S, E>,
 {
-    fn execute_new_svc(&mut self, fut: NewSvcTask<I, N, S, E, W>) -> crate::Result<()> {
-        self.spawn(fut)
-            .map_err(|err| {
-                warn!("executor error: {:?}", err);
-                crate::Error::new_execute("custom executor failed")
-            })
+    fn execute_new_svc(&self, fut: NewSvcTask<I, N, S, E, W>) {
+        self(fut);
     }
 }
-
-// ===== StdError impls =====
-

src/error.rs

@@ -86,12 +86,8 @@ pub(crate) enum User {
 
     /// User tried polling for an upgrade that doesn't exist.
     NoUpgrade,
-
     /// User polled for an upgrade, but low-level API is not using upgrades.
     ManualUpgrade,
-
-    /// Error trying to call `Executor::execute`.
-    Execute,
 }
 
 impl Error {
@@ -277,10 +273,6 @@ impl Error {
         Error::new(Kind::Shutdown).with(cause)
     }
 
-    pub(crate) fn new_execute<E: Into<Cause>>(cause: E) -> Error {
-        Error::new_user(User::Execute).with(cause)
-    }
-
     pub(crate) fn new_h2(cause: ::h2::Error) -> Error {
         if cause.is_io() {
             Error::new_io(cause.into_io().expect("h2::Error::is_io"))
@@ -346,7 +338,6 @@ impl StdError for Error {
             Kind::User(User::AbsoluteUriRequired) => "client requires absolute-form URIs",
             Kind::User(User::NoUpgrade) => "no upgrade available",
             Kind::User(User::ManualUpgrade) => "upgrade expected but low level API in use",
-            Kind::User(User::Execute) => "executor failed to spawn task",
         }
     }
 

src/proto/h2/client.rs

@@ -71,7 +71,7 @@ where
         }
     };
 
-    exec.execute(conn_task)?;
+    exec.execute(conn_task);
 
     Ok(ClientTask {
         conn_drop_ref,
@@ -155,7 +155,7 @@ where
                                         drop(conn_drop_ref);
                                         x
                                     });
-                                self.executor.execute(pipe)?;
+                                self.executor.execute(pipe);
                             }
                         }
                     }
@@ -175,7 +175,7 @@ where
                                 }
                             }
                         });
-                    self.executor.execute(cb.send_when(fut))?;
+                    self.executor.execute(cb.send_when(fut));
                     continue;
                 },
 

src/proto/h2/server.rs

@@ -175,7 +175,7 @@ where
                             crate::Body::h2(stream, content_length)
                         });
                         let fut = H2Stream::new(service.call(req), respond);
-                        exec.execute_h2stream(fut)?;
+                        exec.execute_h2stream(fut);
                     },
                     Some(Err(e)) => {
                         return Poll::Ready(Err(crate::Error::new_h2(e)));

src/server/conn.rs

@@ -843,7 +843,7 @@ where
         loop {
             if let Some(connecting) = ready!(me.serve.as_mut().poll_next_(cx)?) {
                 let fut = NewSvcTask::new(connecting, watcher.clone());
-                me.serve.as_mut().project().protocol.exec.execute_new_svc(fut)?;
+                me.serve.as_mut().project().protocol.exec.execute_new_svc(fut);
             } else {
                 return Poll::Ready(Ok(()));
             }