Introduce tokio-sync crate containing synchronization primitives. (#839)

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.

.appveyor.yml

@@ -11,6 +11,7 @@ install:
   - rustup-init.exe -y --default-host %TARGET%
   - set PATH=%PATH%;C:\Users\appveyor\.cargo\bin
   - set RUST_BACKTRACE=1
+  - set LOOM_MAX_DURATION=10
 
   - rustc -V
   - cargo -V

.travis.yml

@@ -101,6 +101,8 @@ script: |
       cargo check --all --exclude tokio-tls --target $TARGET
       cargo check --tests --all --exclude tokio-tls --target $TARGET
   else
+      # Limit the execution time of loom tests.
+      export LOOM_MAX_DURATION=10
       cargo test --all --no-fail-fast
       cargo doc --all
   fi

Cargo.toml

@@ -26,14 +26,14 @@ members = [
   "./",
   "tokio-async-await",
   "tokio-buf",
-  "tokio-channel",
   "tokio-codec",
   "tokio-current-thread",
   "tokio-executor",
   "tokio-fs",
   "tokio-io",
   "tokio-reactor",
   "tokio-signal",
+  "tokio-sync",
   "tokio-threadpool",
   "tokio-timer",
   "tokio-tcp",
@@ -49,6 +49,7 @@ default = [
   "io",
   "reactor",
   "rt-full",
+  "sync",
   "tcp",
   "timer",
   "udp",
@@ -67,6 +68,7 @@ rt-full = [
   "tokio-executor",
   "tokio-threadpool",
 ]
+sync = ["tokio-sync"]
 tcp = ["tokio-tcp"]
 timer = ["tokio-timer"]
 udp = ["tokio-udp"]
@@ -95,6 +97,7 @@ tokio-fs = { version = "0.1.3", path = "tokio-fs", optional = true }
 tokio-io = { version = "0.1.6", path = "tokio-io", optional = true }
 tokio-executor = { version = "0.1.5", path = "tokio-executor", optional = true }
 tokio-reactor = { version = "0.1.1", path = "tokio-reactor", optional = true }
+tokio-sync = { version = "0.1.0", path = "tokio-sync", optional = true }
 tokio-threadpool = { version = "0.1.8", path = "tokio-threadpool", optional = true }
 tokio-tcp = { version = "0.1.0", path = "tokio-tcp", optional = true }
 tokio-udp = { version = "0.1.0", path = "tokio-udp", optional = true }

src/lib.rs

@@ -100,6 +100,8 @@ extern crate tokio_fs;
 extern crate tokio_reactor;
 #[cfg(feature = "rt-full")]
 extern crate tokio_threadpool;
+#[cfg(feature = "sync")]
+extern crate tokio_sync;
 #[cfg(feature = "timer")]
 extern crate tokio_timer;
 #[cfg(feature = "tcp")]
@@ -126,6 +128,8 @@ pub mod net;
 pub mod prelude;
 #[cfg(feature = "reactor")]
 pub mod reactor;
+#[cfg(feature = "sync")]
+pub mod sync;
 #[cfg(feature = "timer")]
 pub mod timer;
 pub mod util;

src/sync.rs

@@ -0,0 +1,16 @@
+//! Future-aware synchronization
+//!
+//! This module is enabled with the **`sync`** feature flag.
+//!
+//! Tasks sometimes need to communicate with each other. This module contains
+//! two basic abstractions for doing so:
+//!
+//! - [oneshot](oneshot/index.html), a way of sending a single value
+//!   from one task to another.
+//! - [mpsc](mpsc/index.html), a multi-producer, single-consumer channel for
+//!   sending values between tasks.
+
+pub use tokio_sync::{
+    mpsc,
+    oneshot,
+};