Auto merge of #51944 - MajorBreakfast:generic-future-obj, r=cramertj

Make custom trait object for `Future` generic

- `TaskObj` -> `FutureObj<'static, ()>`
- The `impl From<...> for FutureObj<'a, T>` impls are impossible because of the type parameter `T`. The impl has to live in libstd, but `FutureObj<'a, T>` is from libcore. Therefore `Into<FutureObj<'a, T>>` was implemented instead. Edit: This didn‘t compile without warnings. I am now using non-generic Form impls.

See https://github.com/rust-lang-nursery/futures-rs/issues/1058

r? @cramertj

Edit: Added lifetime

3 files changed, 4 insertions, 149 deletions

diff --git a/src/libcore/task/executor.rs b/src/libcore/task/executor.rs
index 73bf80d2f99..f1db5093e98 100644
--- a/src/libcore/task/executor.rs
+++ b/src/libcore/task/executor.rs
@@ -13,7 +13,7 @@
             issue = "50547")]
 
 use fmt;
-use super::{TaskObj, LocalTaskObj};
+use future::{FutureObj, LocalFutureObj};
 
 /// A task executor.
 ///
@@ -29,7 +29,7 @@ pub trait Executor {
     ///
     /// The executor may be unable to spawn tasks, either because it has
     /// been shut down or is resource-constrained.
-    fn spawn_obj(&mut self, task: TaskObj) -> Result<(), SpawnObjError>;
+    fn spawn_obj(&mut self, task: FutureObj<'static, ()>) -> Result<(), SpawnObjError>;
 
     /// Determine whether the executor is able to spawn new tasks.
     ///
@@ -76,7 +76,7 @@ pub struct SpawnObjError {
     pub kind: SpawnErrorKind,
 
     /// The task for which spawning was attempted
-    pub task: TaskObj,
+    pub task: FutureObj<'static, ()>,
 }
 
 /// The result of a failed spawn
@@ -86,5 +86,5 @@ pub struct SpawnLocalObjError {
     pub kind: SpawnErrorKind,
 
     /// The task for which spawning was attempted
-    pub task: LocalTaskObj,
+    pub task: LocalFutureObj<'static, ()>,
 }
diff --git a/src/libcore/task/mod.rs b/src/libcore/task/mod.rs
index d167a374105..c4f07536164 100644
--- a/src/libcore/task/mod.rs
+++ b/src/libcore/task/mod.rs
@@ -25,8 +25,5 @@ pub use self::executor::{
 mod poll;
 pub use self::poll::Poll;
 
-mod task;
-pub use self::task::{TaskObj, LocalTaskObj, UnsafeTask};
-
 mod wake;
 pub use self::wake::{Waker, LocalWaker, UnsafeWake};
diff --git a/src/libcore/task/task.rs b/src/libcore/task/task.rs
deleted file mode 100644
index c5a41873db4..00000000000
--- a/src/libcore/task/task.rs
+++ /dev/null
@@ -1,142 +0,0 @@
-// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-#![unstable(feature = "futures_api",
-            reason = "futures in libcore are unstable",
-            issue = "50547")]
-
-use fmt;
-use future::Future;
-use mem::PinMut;
-use super::{Context, Poll};
-
-/// A custom trait object for polling tasks, roughly akin to
-/// `Box<Future<Output = ()>>`.
-/// Contrary to `TaskObj`, `LocalTaskObj` does not have a `Send` bound.
-pub struct LocalTaskObj {
-    ptr: *mut (),
-    poll_fn: unsafe fn(*mut (), &mut Context) -> Poll<()>,
-    drop_fn: unsafe fn(*mut ()),
-}
-
-impl LocalTaskObj {
-    /// Create a `LocalTaskObj` from a custom trait object representation.
-    #[inline]
-    pub fn new<T: UnsafeTask>(t: T) -> LocalTaskObj {
-        LocalTaskObj {
-            ptr: t.into_raw(),
-            poll_fn: T::poll,
-            drop_fn: T::drop,
-        }
-    }
-
-    /// Converts the `LocalTaskObj` into a `TaskObj`
-    /// To make this operation safe one has to ensure that the `UnsafeTask`
-    /// instance from which this `LocalTaskObj` was created actually implements
-    /// `Send`.
-    pub unsafe fn as_task_obj(self) -> TaskObj {
-        TaskObj(self)
-    }
-}
-
-impl fmt::Debug for LocalTaskObj {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("LocalTaskObj")
-            .finish()
-    }
-}
-
-impl From<TaskObj> for LocalTaskObj {
-    fn from(task: TaskObj) -> LocalTaskObj {
-        task.0
-    }
-}
-
-impl Future for LocalTaskObj {
-    type Output = ();
-
-    #[inline]
-    fn poll(self: PinMut<Self>, cx: &mut Context) -> Poll<()> {
-        unsafe {
-            (self.poll_fn)(self.ptr, cx)
-        }
-    }
-}
-
-impl Drop for LocalTaskObj {
-    fn drop(&mut self) {
-        unsafe {
-            (self.drop_fn)(self.ptr)
-        }
-    }
-}
-
-/// A custom trait object for polling tasks, roughly akin to
-/// `Box<Future<Output = ()> + Send>`.
-pub struct TaskObj(LocalTaskObj);
-
-unsafe impl Send for TaskObj {}
-
-impl TaskObj {
-    /// Create a `TaskObj` from a custom trait object representation.
-    #[inline]
-    pub fn new<T: UnsafeTask + Send>(t: T) -> TaskObj {
-        TaskObj(LocalTaskObj::new(t))
-    }
-}
-
-impl fmt::Debug for TaskObj {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("TaskObj")
-            .finish()
-    }
-}
-
-impl Future for TaskObj {
-    type Output = ();
-
-    #[inline]
-    fn poll(self: PinMut<Self>, cx: &mut Context) -> Poll<()> {
-        let pinned_field = unsafe { PinMut::map_unchecked(self, |x| &mut x.0) };
-        pinned_field.poll(cx)
-    }
-}
-
-/// A custom implementation of a task trait object for `TaskObj`, providing
-/// a hand-rolled vtable.
-///
-/// This custom representation is typically used only in `no_std` contexts,
-/// where the default `Box`-based implementation is not available.
-///
-/// The implementor must guarantee that it is safe to call `poll` repeatedly (in
-/// a non-concurrent fashion) with the result of `into_raw` until `drop` is
-/// called.
-pub unsafe trait UnsafeTask: 'static {
-    /// Convert a owned instance into a (conceptually owned) void pointer.
-    fn into_raw(self) -> *mut ();
-
-    /// Poll the task represented by the given void pointer.
-    ///
-    /// # Safety
-    ///
-    /// The trait implementor must guarantee that it is safe to repeatedly call
-    /// `poll` with the result of `into_raw` until `drop` is called; such calls
-    /// are not, however, allowed to race with each other or with calls to `drop`.
-    unsafe fn poll(task: *mut (), cx: &mut Context) -> Poll<()>;
-
-    /// Drops the task represented by the given void pointer.
-    ///
-    /// # Safety
-    ///
-    /// The trait implementor must guarantee that it is safe to call this
-    /// function once per `into_raw` invocation; that call cannot race with
-    /// other calls to `drop` or `poll`.
-    unsafe fn drop(task: *mut ());
-}