This patch fixes Semaphore by adding a missing code path to the release
routine that handles the case where the waiter's node is queued in the
sempahore but has not yet been assigned the permit.
This fix is used by mpsc to handle the case when the Sender has called
`poll_ready` and is dropped before the permit is acquired.
Fixes#900
Following from https://github.com/tokio-rs/tokio/pull/865, this PR
removes `#[derive(Debug)]` on `mpsc` sender and receiver types in favor
of explicit `impl fmt::Debug` blocks that don't have a `T: fmt::Debug`
bound.
`#[derive(Clone)]` on a type `struct Foo<T>` adds an impl that requires that
`T: Clone`:
```rust
impl<T: Clone> Clone for Foo<T>
```
which is unfortunate in the case of senders, because we don't want to require
that the items being sent are `Clone` for the channel sender to be `Clone`.
This PR adds an explicit `impl Clone` for the bounded and unbounded sender
types which does not have the `T: Clone` bound.
Note that this is _also_ an issue with `#[derive(Debug)]`, but that one is
harder to work around as `chan::Tx` _also_ has `#[derive(Debug)]`, as does
`chan::Chan`, so we'd have to add explicit impls for all of them to make
progress.
Introduce a tokio-sync crate containing useful synchronization primitives for programs
written using Tokio.
The initial release contains:
* An mpsc channel
* A oneshot channel
* A semaphore implementation
* An `AtomicTask` primitive.
The `oneshot` and `mpsc` channels are new implementations providing improved
performance characteristics. In some benchmarks, the new mpsc channel shows
up to 7x improvement over the version provided by the `futures` crate. Unfortunately,
the `oneshot` implementation only provides a slight performance improvement as it
is mostly limited by the `futures` 0.1 task system. Once updated to the `std` version
of `Future` (currently nightly only), much greater performance improvements should
be achievable by `oneshot`.
Additionally, he implementations provided here are checked using
[Loom](http://github.com/carllerche/loom/), which provides greater confidence of
correctness.
Sean McArthur