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
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.
Carl Lerche