runtime: cleanup and add config options (#1807)

* runtime: cleanup and add config options

This patch finishes the cleanup as part of the transition to Tokio 0.2.
A number of changes were made to take advantage of having all Tokio
types in a single crate. Also, fixes using Tokio types from
`spawn_blocking`.

* Many threads, one resource driver

Previously, in the threaded scheduler, a resource driver (mio::Poll /
timer combo) was created per thread. This was more or less fine, except
it required balancing across the available drivers. When using a
resource driver from **outside** of the thread pool, balancing is
tricky. The change was original done to avoid having a dedicated driver
thread.

Now, instead of creating many resource drivers, a single resource driver
is used. Each scheduler thread will attempt to "lock" the resource
driver before parking on it. If the resource driver is already locked,
the thread uses a condition variable to park. Contention should remain
low as, under load, the scheduler avoids using the drivers.

* Add configuration options to enable I/O / time

New configuration options are added to `runtime::Builder` to allow
enabling I/O and time drivers on a runtime instance basis. This is
useful when wanting to create lightweight runtime instances to execute
compute only tasks.

* Bug fixes

The condition variable parker is updated to the same algorithm used in
`std`. This is motivated by some potential deadlock cases discovered by
`loom`.

The basic scheduler is fixed to fairly schedule tasks. `push_front` was
accidentally used instead of `push_back`.

I/O, time, and spawning now work from within `spawn_blocking` closures.

* Misc cleanup

The threaded scheduler is no longer generic over `P :Park`. Instead, it
is hard coded to a specific parker. Tests, including loom tests, are
updated to use `Runtime` directly. This provides greater coverage.

The `blocking` module is moved back into `runtime` as all usage is
within `runtime` itself.

2 files changed, 0 insertions, 69 deletions

diff --git a/tokio/src/runtime/tests/mock_park.rs b/tokio/src/runtime/tests/mock_park.rs
deleted file mode 100644
index 0fe28b36..00000000
--- a/tokio/src/runtime/tests/mock_park.rs
+++ /dev/null
@@ -1,66 +0,0 @@
-#![allow(warnings)]
-
-use crate::runtime::{Park, Unpark};
-
-use std::collections::HashMap;
-use std::sync::atomic::{AtomicBool, Ordering::SeqCst};
-use std::sync::Arc;
-use std::time::Duration;
-
-pub struct MockPark {
-    parks: HashMap<usize, Arc<Inner>>,
-}
-
-#[derive(Clone)]
-struct ParkImpl(Arc<Inner>);
-
-struct Inner {
-    unparked: AtomicBool,
-}
-
-impl MockPark {
-    pub fn new() -> MockPark {
-        MockPark {
-            parks: HashMap::new(),
-        }
-    }
-
-    pub fn is_unparked(&self, index: usize) -> bool {
-        self.parks[&index].unparked.load(SeqCst)
-    }
-
-    pub fn clear(&self, index: usize) {
-        self.parks[&index].unparked.store(false, SeqCst);
-    }
-
-    pub fn mk_park(&mut self, index: usize) -> impl Park {
-        let inner = Arc::new(Inner {
-            unparked: AtomicBool::new(false),
-        });
-        self.parks.insert(index, inner.clone());
-        ParkImpl(inner)
-    }
-}
-
-impl Park for ParkImpl {
-    type Unpark = ParkImpl;
-    type Error = ();
-
-    fn unpark(&self) -> Self::Unpark {
-        self.clone()
-    }
-
-    fn park(&mut self) -> Result<(), Self::Error> {
-        unimplemented!();
-    }
-
-    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
-        unimplemented!();
-    }
-}
-
-impl Unpark for ParkImpl {
-    fn unpark(&self) {
-        self.0.unparked.store(true, SeqCst);
-    }
-}
diff --git a/tokio/src/runtime/tests/mod.rs b/tokio/src/runtime/tests/mod.rs
index 99ed8cd8..a1910a44 100644
--- a/tokio/src/runtime/tests/mod.rs
+++ b/tokio/src/runtime/tests/mod.rs
@@ -2,6 +2,3 @@
 
 #[cfg(loom)]
 pub(crate) mod loom_oneshot;
-
-#[cfg(not(loom))]
-pub(crate) mod mock_park;