Snap for 6435660 from b6b645909d0c1b991d4a094de3319ac88a48a9cf to sdk-release
Change-Id: I4f8524f91e4e25bc9eae2df6809f03a9357e6095
diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..8df2c3b
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,13 @@
+// This file is generated by cargo2android.py.
+
+rust_library_host_rlib {
+ name: "libfutures_core",
+ crate_name: "futures_core",
+ srcs: ["src/lib.rs"],
+ edition: "2018",
+ features: [
+ "alloc",
+ "default",
+ "std",
+ ],
+}
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..243645f
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,33 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "futures-core"
+version = "0.3.4"
+authors = ["Alex Crichton <alex@alexcrichton.com>"]
+description = "The core traits and types in for the `futures` library.\n"
+homepage = "https://rust-lang.github.io/futures-rs"
+documentation = "https://docs.rs/futures-core/0.3.0"
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/futures-rs"
+[package.metadata.docs.rs]
+all-features = true
+
+[dependencies]
+
+[features]
+alloc = []
+cfg-target-has-atomic = []
+default = ["std"]
+std = ["alloc"]
+unstable = []
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
new file mode 100644
index 0000000..061a526
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,28 @@
+[package]
+name = "futures-core"
+edition = "2018"
+version = "0.3.4"
+authors = ["Alex Crichton <alex@alexcrichton.com>"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/rust-lang/futures-rs"
+homepage = "https://rust-lang.github.io/futures-rs"
+documentation = "https://docs.rs/futures-core/0.3.0"
+description = """
+The core traits and types in for the `futures` library.
+"""
+
+[features]
+default = ["std"]
+std = ["alloc"]
+alloc = []
+
+# Unstable features
+# These features are outside of the normal semver guarantees and require the
+# `unstable` feature as an explicit opt-in to unstable API.
+unstable = []
+cfg-target-has-atomic = []
+
+[dependencies]
+
+[package.metadata.docs.rs]
+all-features = true
diff --git a/LICENSE b/LICENSE
new file mode 120000
index 0000000..6b579aa
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1 @@
+LICENSE-APACHE
\ No newline at end of file
diff --git a/LICENSE-APACHE b/LICENSE-APACHE
new file mode 100644
index 0000000..9eb0b09
--- /dev/null
+++ b/LICENSE-APACHE
@@ -0,0 +1,202 @@
+ Apache License
+ Version 2.0, January 2004
+ http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+ "License" shall mean the terms and conditions for use, reproduction,
+ and distribution as defined by Sections 1 through 9 of this document.
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+ "You" (or "Your") shall mean an individual or Legal Entity
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+ "Work" shall mean the work of authorship, whether in Source or
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+ copyright notice that is included in or attached to the work
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+
+ "Derivative Works" shall mean any work, whether in Source or Object
+ form, that is based on (or derived from) the Work and for which the
+ editorial revisions, annotations, elaborations, or other modifications
+ represent, as a whole, an original work of authorship. For the purposes
+ of this License, Derivative Works shall not include works that remain
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+ "Contribution" shall mean any work of authorship, including
+ the original version of the Work and any modifications or additions
+ to that Work or Derivative Works thereof, that is intentionally
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+ "Contributor" shall mean Licensor and any individual or Legal Entity
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+2. Grant of Copyright License. Subject to the terms and conditions of
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+4. Redistribution. You may reproduce and distribute copies of the
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+ modifications, and in Source or Object form, provided that You
+ meet the following conditions:
+
+ (a) You must give any other recipients of the Work or
+ Derivative Works a copy of this License; and
+
+ (b) You must cause any modified files to carry prominent notices
+ stating that You changed the files; and
+
+ (c) You must retain, in the Source form of any Derivative Works
+ that You distribute, all copyright, patent, trademark, and
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+ (d) If the Work includes a "NOTICE" text file as part of its
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+ within a display generated by the Derivative Works, if and
+ wherever such third-party notices normally appear. The contents
+ of the NOTICE file are for informational purposes only and
+ do not modify the License. You may add Your own attribution
+ notices within Derivative Works that You distribute, alongside
+ or as an addendum to the NOTICE text from the Work, provided
+ that such additional attribution notices cannot be construed
+ as modifying the License.
+
+ You may add Your own copyright statement to Your modifications and
+ may provide additional or different license terms and conditions
+ for use, reproduction, or distribution of Your modifications, or
+ for any such Derivative Works as a whole, provided Your use,
+ reproduction, and distribution of the Work otherwise complies with
+ the conditions stated in this License.
+
+5. Submission of Contributions. Unless You explicitly state otherwise,
+ any Contribution intentionally submitted for inclusion in the Work
+ by You to the Licensor shall be under the terms and conditions of
+ this License, without any additional terms or conditions.
+ Notwithstanding the above, nothing herein shall supersede or modify
+ the terms of any separate license agreement you may have executed
+ with Licensor regarding such Contributions.
+
+6. Trademarks. This License does not grant permission to use the trade
+ names, trademarks, service marks, or product names of the Licensor,
+ except as required for reasonable and customary use in describing the
+ origin of the Work and reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty. Unless required by applicable law or
+ agreed to in writing, Licensor provides the Work (and each
+ Contributor provides its Contributions) on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ implied, including, without limitation, any warranties or conditions
+ of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+ PARTICULAR PURPOSE. You are solely responsible for determining the
+ appropriateness of using or redistributing the Work and assume any
+ risks associated with Your exercise of permissions under this License.
+
+8. Limitation of Liability. In no event and under no legal theory,
+ whether in tort (including negligence), contract, or otherwise,
+ unless required by applicable law (such as deliberate and grossly
+ negligent acts) or agreed to in writing, shall any Contributor be
+ liable to You for damages, including any direct, indirect, special,
+ incidental, or consequential damages of any character arising as a
+ result of this License or out of the use or inability to use the
+ Work (including but not limited to damages for loss of goodwill,
+ work stoppage, computer failure or malfunction, or any and all
+ other commercial damages or losses), even if such Contributor
+ has been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability. While redistributing
+ the Work or Derivative Works thereof, You may choose to offer,
+ and charge a fee for, acceptance of support, warranty, indemnity,
+ or other liability obligations and/or rights consistent with this
+ License. However, in accepting such obligations, You may act only
+ on Your own behalf and on Your sole responsibility, not on behalf
+ of any other Contributor, and only if You agree to indemnify,
+ defend, and hold each Contributor harmless for any liability
+ incurred by, or claims asserted against, such Contributor by reason
+ of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
+APPENDIX: How to apply the Apache License to your work.
+
+ To apply the Apache License to your work, attach the following
+ boilerplate notice, with the fields enclosed by brackets "[]"
+ replaced with your own identifying information. (Don't include
+ the brackets!) The text should be enclosed in the appropriate
+ comment syntax for the file format. We also recommend that a
+ file or class name and description of purpose be included on the
+ same "printed page" as the copyright notice for easier
+ identification within third-party archives.
+
+Copyright (c) 2016 Alex Crichton
+Copyright (c) 2017 The Tokio Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
diff --git a/LICENSE-MIT b/LICENSE-MIT
new file mode 100644
index 0000000..8ad082e
--- /dev/null
+++ b/LICENSE-MIT
@@ -0,0 +1,26 @@
+Copyright (c) 2016 Alex Crichton
+Copyright (c) 2017 The Tokio Authors
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..9ddcd3a
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,17 @@
+name: "futures-core"
+description:
+ "The core traits and types in for the `futures` library."
+
+third_party {
+ url {
+ type: HOMEPAGE
+ value: "https://crates.io/crates/futures-core"
+ }
+ url {
+ type: GIT
+ value: "https://github.com/rust-lang/futures-rs"
+ }
+ version: "0.3.4"
+ last_upgrade_date { year: 2020 month: 3 day: 17 }
+ license_type: NOTICE
+}
diff --git a/MODULE_LICENSE_APACHE2 b/MODULE_LICENSE_APACHE2
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_APACHE2
diff --git a/NOTICE b/NOTICE
new file mode 120000
index 0000000..7a694c9
--- /dev/null
+++ b/NOTICE
@@ -0,0 +1 @@
+LICENSE
\ No newline at end of file
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..46fc303
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1 @@
+include platform/prebuilts/rust:/OWNERS
diff --git a/src/future.rs b/src/future.rs
new file mode 100644
index 0000000..35a0fd3
--- /dev/null
+++ b/src/future.rs
@@ -0,0 +1,104 @@
+//! Futures.
+
+use core::ops::DerefMut;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+pub use core::future::Future;
+
+/// An owned dynamically typed [`Future`] for use in cases where you can't
+/// statically type your result or need to add some indirection.
+#[cfg(feature = "alloc")]
+pub type BoxFuture<'a, T> = Pin<alloc::boxed::Box<dyn Future<Output = T> + Send + 'a>>;
+
+/// `BoxFuture`, but without the `Send` requirement.
+#[cfg(feature = "alloc")]
+pub type LocalBoxFuture<'a, T> = Pin<alloc::boxed::Box<dyn Future<Output = T> + 'a>>;
+
+/// A future which tracks whether or not the underlying future
+/// should no longer be polled.
+///
+/// `is_terminated` will return `true` if a future should no longer be polled.
+/// Usually, this state occurs after `poll` (or `try_poll`) returned
+/// `Poll::Ready`. However, `is_terminated` may also return `true` if a future
+/// has become inactive and can no longer make progress and should be ignored
+/// or dropped rather than being `poll`ed again.
+pub trait FusedFuture: Future {
+ /// Returns `true` if the underlying future should no longer be polled.
+ fn is_terminated(&self) -> bool;
+}
+
+impl<F: FusedFuture + ?Sized + Unpin> FusedFuture for &mut F {
+ fn is_terminated(&self) -> bool {
+ <F as FusedFuture>::is_terminated(&**self)
+ }
+}
+
+impl<P> FusedFuture for Pin<P>
+where
+ P: DerefMut + Unpin,
+ P::Target: FusedFuture,
+{
+ fn is_terminated(&self) -> bool {
+ <P::Target as FusedFuture>::is_terminated(&**self)
+ }
+}
+
+mod private_try_future {
+ use super::Future;
+
+ pub trait Sealed {}
+
+ impl<F, T, E> Sealed for F where F: ?Sized + Future<Output = Result<T, E>> {}
+}
+
+/// A convenience for futures that return `Result` values that includes
+/// a variety of adapters tailored to such futures.
+pub trait TryFuture: Future + private_try_future::Sealed {
+ /// The type of successful values yielded by this future
+ type Ok;
+
+ /// The type of failures yielded by this future
+ type Error;
+
+ /// Poll this `TryFuture` as if it were a `Future`.
+ ///
+ /// This method is a stopgap for a compiler limitation that prevents us from
+ /// directly inheriting from the `Future` trait; in the future it won't be
+ /// needed.
+ fn try_poll(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ ) -> Poll<Result<Self::Ok, Self::Error>>;
+}
+
+impl<F, T, E> TryFuture for F
+ where F: ?Sized + Future<Output = Result<T, E>>
+{
+ type Ok = T;
+ type Error = E;
+
+ #[inline]
+ fn try_poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<F::Output> {
+ self.poll(cx)
+ }
+}
+
+#[cfg(feature = "alloc")]
+mod if_alloc {
+ use alloc::boxed::Box;
+ use super::*;
+
+ impl<F: FusedFuture + ?Sized + Unpin> FusedFuture for Box<F> {
+ fn is_terminated(&self) -> bool {
+ <F as FusedFuture>::is_terminated(&**self)
+ }
+ }
+
+ #[cfg(feature = "std")]
+ impl<F: FusedFuture> FusedFuture for std::panic::AssertUnwindSafe<F> {
+ fn is_terminated(&self) -> bool {
+ <F as FusedFuture>::is_terminated(&**self)
+ }
+ }
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..85eff3e
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,36 @@
+//! Core traits and types for asynchronous operations in Rust.
+
+#![cfg_attr(feature = "cfg-target-has-atomic", feature(cfg_target_has_atomic))]
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#![warn(missing_docs, missing_debug_implementations, rust_2018_idioms, unreachable_pub)]
+// It cannot be included in the published code because this lints have false positives in the minimum required version.
+#![cfg_attr(test, warn(single_use_lifetimes))]
+#![warn(clippy::all)]
+
+#![doc(test(attr(deny(warnings), allow(dead_code, unused_assignments, unused_variables))))]
+
+#![doc(html_root_url = "https://docs.rs/futures-core/0.3.0")]
+
+#[cfg(all(feature = "cfg-target-has-atomic", not(feature = "unstable")))]
+compile_error!("The `cfg-target-has-atomic` feature requires the `unstable` feature as an explicit opt-in to unstable features");
+
+#[cfg(feature = "alloc")]
+extern crate alloc;
+
+pub mod future;
+#[doc(hidden)] pub use self::future::{Future, FusedFuture, TryFuture};
+
+pub mod stream;
+#[doc(hidden)] pub use self::stream::{Stream, FusedStream, TryStream};
+
+#[macro_use]
+pub mod task;
+
+// Not public API.
+#[doc(hidden)]
+pub mod core_reexport {
+ #[doc(hidden)]
+ pub use core::*;
+}
diff --git a/src/stream.rs b/src/stream.rs
new file mode 100644
index 0000000..1f0f9a6
--- /dev/null
+++ b/src/stream.rs
@@ -0,0 +1,238 @@
+//! Asynchronous streams.
+
+use core::ops::DerefMut;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+/// An owned dynamically typed [`Stream`] for use in cases where you can't
+/// statically type your result or need to add some indirection.
+#[cfg(feature = "alloc")]
+pub type BoxStream<'a, T> = Pin<alloc::boxed::Box<dyn Stream<Item = T> + Send + 'a>>;
+
+/// `BoxStream`, but without the `Send` requirement.
+#[cfg(feature = "alloc")]
+pub type LocalBoxStream<'a, T> = Pin<alloc::boxed::Box<dyn Stream<Item = T> + 'a>>;
+
+/// A stream of values produced asynchronously.
+///
+/// If `Future<Output = T>` is an asynchronous version of `T`, then `Stream<Item
+/// = T>` is an asynchronous version of `Iterator<Item = T>`. A stream
+/// represents a sequence of value-producing events that occur asynchronously to
+/// the caller.
+///
+/// The trait is modeled after `Future`, but allows `poll_next` to be called
+/// even after a value has been produced, yielding `None` once the stream has
+/// been fully exhausted.
+#[must_use = "streams do nothing unless polled"]
+pub trait Stream {
+ /// Values yielded by the stream.
+ type Item;
+
+ /// Attempt to pull out the next value of this stream, registering the
+ /// current task for wakeup if the value is not yet available, and returning
+ /// `None` if the stream is exhausted.
+ ///
+ /// # Return value
+ ///
+ /// There are several possible return values, each indicating a distinct
+ /// stream state:
+ ///
+ /// - `Poll::Pending` means that this stream's next value is not ready
+ /// yet. Implementations will ensure that the current task will be notified
+ /// when the next value may be ready.
+ ///
+ /// - `Poll::Ready(Some(val))` means that the stream has successfully
+ /// produced a value, `val`, and may produce further values on subsequent
+ /// `poll_next` calls.
+ ///
+ /// - `Poll::Ready(None)` means that the stream has terminated, and
+ /// `poll_next` should not be invoked again.
+ ///
+ /// # Panics
+ ///
+ /// Once a stream is finished, i.e. `Ready(None)` has been returned, further
+ /// calls to `poll_next` may result in a panic or other "bad behavior". If
+ /// this is difficult to guard against then the `fuse` adapter can be used
+ /// to ensure that `poll_next` always returns `Ready(None)` in subsequent
+ /// calls.
+ fn poll_next(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ ) -> Poll<Option<Self::Item>>;
+
+ /// Returns the bounds on the remaining length of the stream.
+ ///
+ /// Specifically, `size_hint()` returns a tuple where the first element
+ /// is the lower bound, and the second element is the upper bound.
+ ///
+ /// The second half of the tuple that is returned is an [`Option`]`<`[`usize`]`>`.
+ /// A [`None`] here means that either there is no known upper bound, or the
+ /// upper bound is larger than [`usize`].
+ ///
+ /// # Implementation notes
+ ///
+ /// It is not enforced that a stream implementation yields the declared
+ /// number of elements. A buggy stream may yield less than the lower bound
+ /// or more than the upper bound of elements.
+ ///
+ /// `size_hint()` is primarily intended to be used for optimizations such as
+ /// reserving space for the elements of the stream, but must not be
+ /// trusted to e.g., omit bounds checks in unsafe code. An incorrect
+ /// implementation of `size_hint()` should not lead to memory safety
+ /// violations.
+ ///
+ /// That said, the implementation should provide a correct estimation,
+ /// because otherwise it would be a violation of the trait's protocol.
+ ///
+ /// The default implementation returns `(0, `[`None`]`)` which is correct for any
+ /// stream.
+ #[inline]
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (0, None)
+ }
+}
+
+impl<S: ?Sized + Stream + Unpin> Stream for &mut S {
+ type Item = S::Item;
+
+ fn poll_next(
+ mut self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ ) -> Poll<Option<Self::Item>> {
+ S::poll_next(Pin::new(&mut **self), cx)
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (**self).size_hint()
+ }
+}
+
+impl<P> Stream for Pin<P>
+where
+ P: DerefMut + Unpin,
+ P::Target: Stream,
+{
+ type Item = <P::Target as Stream>::Item;
+
+ fn poll_next(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ ) -> Poll<Option<Self::Item>> {
+ self.get_mut().as_mut().poll_next(cx)
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (**self).size_hint()
+ }
+}
+
+/// A stream which tracks whether or not the underlying stream
+/// should no longer be polled.
+///
+/// `is_terminated` will return `true` if a future should no longer be polled.
+/// Usually, this state occurs after `poll_next` (or `try_poll_next`) returned
+/// `Poll::Ready(None)`. However, `is_terminated` may also return `true` if a
+/// stream has become inactive and can no longer make progress and should be
+/// ignored or dropped rather than being polled again.
+pub trait FusedStream: Stream {
+ /// Returns `true` if the stream should no longer be polled.
+ fn is_terminated(&self) -> bool;
+}
+
+impl<F: ?Sized + FusedStream + Unpin> FusedStream for &mut F {
+ fn is_terminated(&self) -> bool {
+ <F as FusedStream>::is_terminated(&**self)
+ }
+}
+
+impl<P> FusedStream for Pin<P>
+where
+ P: DerefMut + Unpin,
+ P::Target: FusedStream,
+{
+ fn is_terminated(&self) -> bool {
+ <P::Target as FusedStream>::is_terminated(&**self)
+ }
+}
+
+mod private_try_stream {
+ use super::Stream;
+
+ pub trait Sealed {}
+
+ impl<S, T, E> Sealed for S where S: ?Sized + Stream<Item = Result<T, E>> {}
+}
+
+/// A convenience for streams that return `Result` values that includes
+/// a variety of adapters tailored to such futures.
+pub trait TryStream: Stream + private_try_stream::Sealed {
+ /// The type of successful values yielded by this future
+ type Ok;
+
+ /// The type of failures yielded by this future
+ type Error;
+
+ /// Poll this `TryStream` as if it were a `Stream`.
+ ///
+ /// This method is a stopgap for a compiler limitation that prevents us from
+ /// directly inheriting from the `Stream` trait; in the future it won't be
+ /// needed.
+ fn try_poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>)
+ -> Poll<Option<Result<Self::Ok, Self::Error>>>;
+}
+
+impl<S, T, E> TryStream for S
+ where S: ?Sized + Stream<Item = Result<T, E>>
+{
+ type Ok = T;
+ type Error = E;
+
+ fn try_poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>)
+ -> Poll<Option<Result<Self::Ok, Self::Error>>>
+ {
+ self.poll_next(cx)
+ }
+}
+
+#[cfg(feature = "alloc")]
+mod if_alloc {
+ use alloc::boxed::Box;
+ use super::*;
+
+ impl<S: ?Sized + Stream + Unpin> Stream for Box<S> {
+ type Item = S::Item;
+
+ fn poll_next(
+ mut self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ ) -> Poll<Option<Self::Item>> {
+ Pin::new(&mut **self).poll_next(cx)
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ (**self).size_hint()
+ }
+ }
+
+ #[cfg(feature = "std")]
+ impl<S: Stream> Stream for std::panic::AssertUnwindSafe<S> {
+ type Item = S::Item;
+
+ fn poll_next(
+ self: Pin<&mut Self>,
+ cx: &mut Context<'_>,
+ ) -> Poll<Option<S::Item>> {
+ unsafe { self.map_unchecked_mut(|x| &mut x.0) }.poll_next(cx)
+ }
+
+ fn size_hint(&self) -> (usize, Option<usize>) {
+ self.0.size_hint()
+ }
+ }
+
+ impl<S: ?Sized + FusedStream + Unpin> FusedStream for Box<S> {
+ fn is_terminated(&self) -> bool {
+ <S as FusedStream>::is_terminated(&**self)
+ }
+ }
+}
diff --git a/src/task/__internal/atomic_waker.rs b/src/task/__internal/atomic_waker.rs
new file mode 100644
index 0000000..506737e
--- /dev/null
+++ b/src/task/__internal/atomic_waker.rs
@@ -0,0 +1,412 @@
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::sync::atomic::AtomicUsize;
+use core::sync::atomic::Ordering::{Acquire, Release, AcqRel};
+use core::task::Waker;
+
+/// A synchronization primitive for task wakeup.
+///
+/// Sometimes the task interested in a given event will change over time.
+/// An `AtomicWaker` can coordinate concurrent notifications with the consumer
+/// potentially "updating" the underlying task to wake up. This is useful in
+/// scenarios where a computation completes in another thread and wants to
+/// notify the consumer, but the consumer is in the process of being migrated to
+/// a new logical task.
+///
+/// Consumers should call `register` before checking the result of a computation
+/// and producers should call `wake` after producing the computation (this
+/// differs from the usual `thread::park` pattern). It is also permitted for
+/// `wake` to be called **before** `register`. This results in a no-op.
+///
+/// A single `AtomicWaker` may be reused for any number of calls to `register` or
+/// `wake`.
+///
+/// # Memory ordering
+///
+/// Calling `register` "acquires" all memory "released" by calls to `wake`
+/// before the call to `register`. Later calls to `wake` will wake the
+/// registered waker (on contention this wake might be triggered in `register`).
+///
+/// For concurrent calls to `register` (should be avoided) the ordering is only
+/// guaranteed for the winning call.
+///
+/// # Examples
+///
+/// Here is a simple example providing a `Flag` that can be signalled manually
+/// when it is ready.
+///
+/// ```
+/// use futures::future::Future;
+/// use futures::task::{Context, Poll, AtomicWaker};
+/// use std::sync::Arc;
+/// use std::sync::atomic::AtomicBool;
+/// use std::sync::atomic::Ordering::Relaxed;
+/// use std::pin::Pin;
+///
+/// struct Inner {
+/// waker: AtomicWaker,
+/// set: AtomicBool,
+/// }
+///
+/// #[derive(Clone)]
+/// struct Flag(Arc<Inner>);
+///
+/// impl Flag {
+/// pub fn new() -> Self {
+/// Flag(Arc::new(Inner {
+/// waker: AtomicWaker::new(),
+/// set: AtomicBool::new(false),
+/// }))
+/// }
+///
+/// pub fn signal(&self) {
+/// self.0.set.store(true, Relaxed);
+/// self.0.waker.wake();
+/// }
+/// }
+///
+/// impl Future for Flag {
+/// type Output = ();
+///
+/// fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+/// // quick check to avoid registration if already done.
+/// if self.0.set.load(Relaxed) {
+/// return Poll::Ready(());
+/// }
+///
+/// self.0.waker.register(cx.waker());
+///
+/// // Need to check condition **after** `register` to avoid a race
+/// // condition that would result in lost notifications.
+/// if self.0.set.load(Relaxed) {
+/// Poll::Ready(())
+/// } else {
+/// Poll::Pending
+/// }
+/// }
+/// }
+/// ```
+pub struct AtomicWaker {
+ state: AtomicUsize,
+ waker: UnsafeCell<Option<Waker>>,
+}
+
+// `AtomicWaker` is a multi-consumer, single-producer transfer cell. The cell
+// stores a `Waker` value produced by calls to `register` and many threads can
+// race to take the waker (to wake it) by calling `wake`.
+//
+// If a new `Waker` instance is produced by calling `register` before an
+// existing one is consumed, then the existing one is overwritten.
+//
+// While `AtomicWaker` is single-producer, the implementation ensures memory
+// safety. In the event of concurrent calls to `register`, there will be a
+// single winner whose waker will get stored in the cell. The losers will not
+// have their tasks woken. As such, callers should ensure to add synchronization
+// to calls to `register`.
+//
+// The implementation uses a single `AtomicUsize` value to coordinate access to
+// the `Waker` cell. There are two bits that are operated on independently.
+// These are represented by `REGISTERING` and `WAKING`.
+//
+// The `REGISTERING` bit is set when a producer enters the critical section. The
+// `WAKING` bit is set when a consumer enters the critical section. Neither bit
+// being set is represented by `WAITING`.
+//
+// A thread obtains an exclusive lock on the waker cell by transitioning the
+// state from `WAITING` to `REGISTERING` or `WAKING`, depending on the operation
+// the thread wishes to perform. When this transition is made, it is guaranteed
+// that no other thread will access the waker cell.
+//
+// # Registering
+//
+// On a call to `register`, an attempt to transition the state from WAITING to
+// REGISTERING is made. On success, the caller obtains a lock on the waker cell.
+//
+// If the lock is obtained, then the thread sets the waker cell to the waker
+// provided as an argument. Then it attempts to transition the state back from
+// `REGISTERING` -> `WAITING`.
+//
+// If this transition is successful, then the registering process is complete
+// and the next call to `wake` will observe the waker.
+//
+// If the transition fails, then there was a concurrent call to `wake` that was
+// unable to access the waker cell (due to the registering thread holding the
+// lock). To handle this, the registering thread removes the waker it just set
+// from the cell and calls `wake` on it. This call to wake represents the
+// attempt to wake by the other thread (that set the `WAKING` bit). The state is
+// then transitioned from `REGISTERING | WAKING` back to `WAITING`. This
+// transition must succeed because, at this point, the state cannot be
+// transitioned by another thread.
+//
+// # Waking
+//
+// On a call to `wake`, an attempt to transition the state from `WAITING` to
+// `WAKING` is made. On success, the caller obtains a lock on the waker cell.
+//
+// If the lock is obtained, then the thread takes ownership of the current value
+// in the waker cell, and calls `wake` on it. The state is then transitioned
+// back to `WAITING`. This transition must succeed as, at this point, the state
+// cannot be transitioned by another thread.
+//
+// If the thread is unable to obtain the lock, the `WAKING` bit is still. This
+// is because it has either been set by the current thread but the previous
+// value included the `REGISTERING` bit **or** a concurrent thread is in the
+// `WAKING` critical section. Either way, no action must be taken.
+//
+// If the current thread is the only concurrent call to `wake` and another
+// thread is in the `register` critical section, when the other thread **exits**
+// the `register` critical section, it will observe the `WAKING` bit and handle
+// the wake itself.
+//
+// If another thread is in the `wake` critical section, then it will handle
+// waking the task.
+//
+// # A potential race (is safely handled).
+//
+// Imagine the following situation:
+//
+// * Thread A obtains the `wake` lock and wakes a task.
+//
+// * Before thread A releases the `wake` lock, the woken task is scheduled.
+//
+// * Thread B attempts to wake the task. In theory this should result in the
+// task being woken, but it cannot because thread A still holds the wake lock.
+//
+// This case is handled by requiring users of `AtomicWaker` to call `register`
+// **before** attempting to observe the application state change that resulted
+// in the task being awoken. The wakers also change the application state before
+// calling wake.
+//
+// Because of this, the waker will do one of two things.
+//
+// 1) Observe the application state change that Thread B is woken for. In this
+// case, it is OK for Thread B's wake to be lost.
+//
+// 2) Call register before attempting to observe the application state. Since
+// Thread A still holds the `wake` lock, the call to `register` will result
+// in the task waking itself and get scheduled again.
+
+/// Idle state
+const WAITING: usize = 0;
+
+/// A new waker value is being registered with the `AtomicWaker` cell.
+const REGISTERING: usize = 0b01;
+
+/// The waker currently registered with the `AtomicWaker` cell is being woken.
+const WAKING: usize = 0b10;
+
+impl AtomicWaker {
+ /// Create an `AtomicWaker`.
+ pub const fn new() -> Self {
+ // Make sure that task is Sync
+ trait AssertSync: Sync {}
+ impl AssertSync for Waker {}
+
+ AtomicWaker {
+ state: AtomicUsize::new(WAITING),
+ waker: UnsafeCell::new(None),
+ }
+ }
+
+ /// Registers the waker to be notified on calls to `wake`.
+ ///
+ /// The new task will take place of any previous tasks that were registered
+ /// by previous calls to `register`. Any calls to `wake` that happen after
+ /// a call to `register` (as defined by the memory ordering rules), will
+ /// notify the `register` caller's task and deregister the waker from future
+ /// notifications. Because of this, callers should ensure `register` gets
+ /// invoked with a new `Waker` **each** time they require a wakeup.
+ ///
+ /// It is safe to call `register` with multiple other threads concurrently
+ /// calling `wake`. This will result in the `register` caller's current
+ /// task being notified once.
+ ///
+ /// This function is safe to call concurrently, but this is generally a bad
+ /// idea. Concurrent calls to `register` will attempt to register different
+ /// tasks to be notified. One of the callers will win and have its task set,
+ /// but there is no guarantee as to which caller will succeed.
+ ///
+ /// # Examples
+ ///
+ /// Here is how `register` is used when implementing a flag.
+ ///
+ /// ```
+ /// use futures::future::Future;
+ /// use futures::task::{Context, Poll, AtomicWaker};
+ /// use std::sync::atomic::AtomicBool;
+ /// use std::sync::atomic::Ordering::Relaxed;
+ /// use std::pin::Pin;
+ ///
+ /// struct Flag {
+ /// waker: AtomicWaker,
+ /// set: AtomicBool,
+ /// }
+ ///
+ /// impl Future for Flag {
+ /// type Output = ();
+ ///
+ /// fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+ /// // Register **before** checking `set` to avoid a race condition
+ /// // that would result in lost notifications.
+ /// self.waker.register(cx.waker());
+ ///
+ /// if self.set.load(Relaxed) {
+ /// Poll::Ready(())
+ /// } else {
+ /// Poll::Pending
+ /// }
+ /// }
+ /// }
+ /// ```
+ pub fn register(&self, waker: &Waker) {
+ match self.state.compare_and_swap(WAITING, REGISTERING, Acquire) {
+ WAITING => {
+ unsafe {
+ // Locked acquired, update the waker cell
+ *self.waker.get() = Some(waker.clone());
+
+ // Release the lock. If the state transitioned to include
+ // the `WAKING` bit, this means that at least one wake has
+ // been called concurrently.
+ //
+ // Start by assuming that the state is `REGISTERING` as this
+ // is what we just set it to. If this holds, we know that no
+ // other writes were performed in the meantime, so there is
+ // nothing to acquire, only release. In case of concurrent
+ // wakers, we need to acquire their releases, so success needs
+ // to do both.
+ let res = self.state.compare_exchange(
+ REGISTERING, WAITING, AcqRel, Acquire);
+
+ match res {
+ Ok(_) => {
+ // memory ordering: acquired self.state during CAS
+ // - if previous wakes went through it syncs with
+ // their final release (`fetch_and`)
+ // - if there was no previous wake the next wake
+ // will wake us, no sync needed.
+ }
+ Err(actual) => {
+ // This branch can only be reached if at least one
+ // concurrent thread called `wake`. In this
+ // case, `actual` **must** be `REGISTERING |
+ // `WAKING`.
+ debug_assert_eq!(actual, REGISTERING | WAKING);
+
+ // Take the waker to wake once the atomic operation has
+ // completed.
+ let waker = (*self.waker.get()).take().unwrap();
+
+ // We need to return to WAITING state (clear our lock and
+ // concurrent WAKING flag). This needs to acquire all
+ // WAKING fetch_or releases and it needs to release our
+ // update to self.waker, so we need a `swap` operation.
+ self.state.swap(WAITING, AcqRel);
+
+ // memory ordering: we acquired the state for all
+ // concurrent wakes, but future wakes might still
+ // need to wake us in case we can't make progress
+ // from the pending wakes.
+ //
+ // So we simply schedule to come back later (we could
+ // also simply leave the registration in place above).
+ waker.wake();
+ }
+ }
+ }
+ }
+ WAKING => {
+ // Currently in the process of waking the task, i.e.,
+ // `wake` is currently being called on the old task handle.
+ //
+ // memory ordering: we acquired the state for all
+ // concurrent wakes, but future wakes might still
+ // need to wake us in case we can't make progress
+ // from the pending wakes.
+ //
+ // So we simply schedule to come back later (we
+ // could also spin here trying to acquire the lock
+ // to register).
+ waker.wake_by_ref();
+ }
+ state => {
+ // In this case, a concurrent thread is holding the
+ // "registering" lock. This probably indicates a bug in the
+ // caller's code as racing to call `register` doesn't make much
+ // sense.
+ //
+ // memory ordering: don't care. a concurrent register() is going
+ // to succeed and provide proper memory ordering.
+ //
+ // We just want to maintain memory safety. It is ok to drop the
+ // call to `register`.
+ debug_assert!(
+ state == REGISTERING ||
+ state == REGISTERING | WAKING);
+ }
+ }
+ }
+
+ /// Calls `wake` on the last `Waker` passed to `register`.
+ ///
+ /// If `register` has not been called yet, then this does nothing.
+ pub fn wake(&self) {
+ if let Some(waker) = self.take() {
+ waker.wake();
+ }
+ }
+
+ /// Returns the last `Waker` passed to `register`, so that the user can wake it.
+ ///
+ ///
+ /// Sometimes, just waking the AtomicWaker is not fine grained enough. This allows the user
+ /// to take the waker and then wake it separately, rather than performing both steps in one
+ /// atomic action.
+ ///
+ /// If a waker has not been registered, this returns `None`.
+ pub fn take(&self) -> Option<Waker> {
+ // AcqRel ordering is used in order to acquire the value of the `task`
+ // cell as well as to establish a `release` ordering with whatever
+ // memory the `AtomicWaker` is associated with.
+ match self.state.fetch_or(WAKING, AcqRel) {
+ WAITING => {
+ // The waking lock has been acquired.
+ let waker = unsafe { (*self.waker.get()).take() };
+
+ // Release the lock
+ self.state.fetch_and(!WAKING, Release);
+
+ waker
+ }
+ state => {
+ // There is a concurrent thread currently updating the
+ // associated task.
+ //
+ // Nothing more to do as the `WAKING` bit has been set. It
+ // doesn't matter if there are concurrent registering threads or
+ // not.
+ //
+ debug_assert!(
+ state == REGISTERING ||
+ state == REGISTERING | WAKING ||
+ state == WAKING);
+ None
+ }
+ }
+ }
+}
+
+impl Default for AtomicWaker {
+ fn default() -> Self {
+ AtomicWaker::new()
+ }
+}
+
+impl fmt::Debug for AtomicWaker {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ write!(f, "AtomicWaker")
+ }
+}
+
+unsafe impl Send for AtomicWaker {}
+unsafe impl Sync for AtomicWaker {}
diff --git a/src/task/__internal/mod.rs b/src/task/__internal/mod.rs
new file mode 100644
index 0000000..77e3678
--- /dev/null
+++ b/src/task/__internal/mod.rs
@@ -0,0 +1,4 @@
+#[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
+mod atomic_waker;
+#[cfg_attr(feature = "cfg-target-has-atomic", cfg(target_has_atomic = "ptr"))]
+pub use self::atomic_waker::AtomicWaker;
diff --git a/src/task/mod.rs b/src/task/mod.rs
new file mode 100644
index 0000000..362b376
--- /dev/null
+++ b/src/task/mod.rs
@@ -0,0 +1,9 @@
+//! Task notification.
+
+#[macro_use]
+mod poll;
+
+#[doc(hidden)]
+pub mod __internal;
+
+pub use core::task::{Context, Poll, Waker, RawWaker, RawWakerVTable};
diff --git a/src/task/poll.rs b/src/task/poll.rs
new file mode 100644
index 0000000..fc61683
--- /dev/null
+++ b/src/task/poll.rs
@@ -0,0 +1,11 @@
+/// Extracts the successful type of a `Poll<T>`.
+///
+/// This macro bakes in propagation of `Pending` signals by returning early.
+#[macro_export]
+macro_rules! ready {
+ ($e:expr $(,)?) => (match $e {
+ $crate::core_reexport::task::Poll::Ready(t) => t,
+ $crate::core_reexport::task::Poll::Pending =>
+ return $crate::core_reexport::task::Poll::Pending,
+ })
+}
