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.

tokio-macros/src/lib.rs

@@ -110,6 +110,7 @@ pub fn main(args: TokenStream, item: TokenStream) -> TokenStream {
             fn #name(#inputs) #ret {
                 tokio::runtime::Builder::new()
                     .basic_scheduler()
+                    .enable_all()
                     .build()
                     .unwrap()
                     .block_on(async { #body })
@@ -211,6 +212,7 @@ pub fn test(args: TokenStream, item: TokenStream) -> TokenStream {
             fn #name() #ret {
                 tokio::runtime::Builder::new()
                     .basic_scheduler()
+                    .enable_all()
                     .build()
                     .unwrap()
                     .block_on(async { #body })

tokio-test/src/io.rs

@@ -1,3 +1,5 @@
+#![cfg(not(loom))]
+
 //! A mock type implementing [`AsyncRead`] and [`AsyncWrite`].
 //!
 //!

tokio-test/src/lib.rs

@@ -14,6 +14,7 @@
 //! Tokio and Futures based testing utilites
 
 pub mod io;
+
 mod macros;
 pub mod task;
 
@@ -27,7 +28,11 @@ pub mod task;
 pub fn block_on<F: std::future::Future>(future: F) -> F::Output {
     use tokio::runtime;
 
-    let mut rt = runtime::Builder::new().basic_scheduler().build().unwrap();
+    let mut rt = runtime::Builder::new()
+        .basic_scheduler()
+        .enable_all()
+        .build()
+        .unwrap();
 
     rt.block_on(future)
 }

tokio/Cargo.toml

@@ -99,7 +99,7 @@ fnv = { version = "1.0.6", optional = true }
 futures-core = { version = "0.3.0", optional = true }
 lazy_static = { version = "1.0.2", optional = true }
 memchr = { version = "2.2", optional = true }
-mio = { version = "0.6.14", optional = true }
+mio = { version = "0.6.20", optional = true }
 num_cpus = { version = "1.8.0", optional = true }
 # Backs `DelayQueue`
 slab = { version = "0.4.1", optional = true }

tokio/src/fs/mod.rs

@@ -1,3 +1,5 @@
+#![cfg(not(loom))]
+
 //! Asynchronous file and standard stream adaptation.
 //!
 //! This module contains utility methods and adapter types for input/output to
@@ -96,6 +98,6 @@ mod sys {
     pub(crate) use std::fs::File;
 
     // TODO: don't rename
-    pub(crate) use crate::blocking::spawn_blocking as run;
+    pub(crate) use crate::runtime::spawn_blocking as run;
     pub(crate) use crate::task::JoinHandle as Blocking;
 }

tokio/src/io/driver/mod.rs

@@ -4,7 +4,7 @@ mod scheduled_io;
 pub(crate) use scheduled_io::ScheduledIo; // pub(crate) for tests
 
 use crate::loom::sync::atomic::AtomicUsize;
-use crate::runtime::{Park, Unpark};
+use crate::park::{Park, Unpark};
 use crate::util::slab::{Address, Slab};
 
 use mio::event::Evented;

tokio/src/io/mod.rs

@@ -1,3 +1,5 @@
+#![cfg_attr(loom, allow(dead_code, unreachable_pub))]
+
 //! Asynchronous I/O.
 //!
 //! This module is the asynchronous version of `std::io`. Primarily, it
@@ -204,7 +206,7 @@ cfg_io_blocking! {
     /// Types in this module can be mocked out in tests.
     mod sys {
         // TODO: don't rename
-        pub(crate) use crate::blocking::spawn_blocking as run;
+        pub(crate) use crate::runtime::spawn_blocking as run;
         pub(crate) use crate::task::JoinHandle as Blocking;
     }
 }

tokio/src/lib.rs

@@ -208,20 +208,17 @@
 #[macro_use]
 mod macros;
 
-// Blocking task implementation
-pub(crate) mod blocking;
-
 cfg_fs! {
     pub mod fs;
 }
 
 mod future;
 
 pub mod io;
-
 pub mod net;
 
 mod loom;
+mod park;
 
 pub mod prelude;
 

tokio/src/loom/std/mod.rs

@@ -1,4 +1,4 @@
-#![cfg_attr(not(feature = "full"), allow(unused_imports, dead_code))]
+#![cfg_attr(any(not(feature = "full"), loom), allow(unused_imports, dead_code))]
 
 mod atomic_u32;
 mod atomic_u64;
@@ -45,8 +45,8 @@ pub(crate) mod sync {
         pub(crate) use crate::loom::std::atomic_u64::AtomicU64;
         pub(crate) use crate::loom::std::atomic_usize::AtomicUsize;
 
-        pub(crate) use std::sync::atomic::spin_loop_hint;
         pub(crate) use std::sync::atomic::{fence, AtomicPtr};
+        pub(crate) use std::sync::atomic::{spin_loop_hint, AtomicBool};
     }
 }
 

tokio/src/macros/cfg.rs

@@ -1,8 +1,12 @@
 #![allow(unused_macros)]
 
-macro_rules! cfg_atomic_waker {
+macro_rules! cfg_resource_drivers {
     ($($item:item)*) => {
-        $( #[cfg(any(feature = "io-driver", feature = "time"))] $item )*
+        $(
+            #[cfg(any(feature = "io-driver", feature = "time"))]
+            #[cfg(not(loom))]
+            $item
+        )*
     }
 }
 

tokio/src/net/addr.rs

@@ -124,7 +124,7 @@ cfg_dns! {
         type Future = sealed::MaybeReady;
 
         fn to_socket_addrs(&self) -> Self::Future {
-            use crate::blocking;
+            use crate::runtime::spawn_blocking;
             use sealed::MaybeReady;
 
             // First check if the input parses as a socket address
@@ -137,7 +137,7 @@ cfg_dns! {
             // Run DNS lookup on the blocking pool
             let s = self.to_owned();
 
-            MaybeReady::Blocking(blocking::spawn_blocking(move || {
+            MaybeReady::Blocking(spawn_blocking(move || {
                 std::net::ToSocketAddrs::to_socket_addrs(&s)
             }))
         }
@@ -152,7 +152,7 @@ cfg_dns! {
         type Future = sealed::MaybeReady;
 
         fn to_socket_addrs(&self) -> Self::Future {
-            use crate::blocking;
+            use crate::runtime::spawn_blocking;
             use sealed::MaybeReady;
 
             let (host, port) = *self;
@@ -174,7 +174,7 @@ cfg_dns! {
 
             let host = host.to_owned();
 
-            MaybeReady::Blocking(blocking::spawn_blocking(move || {
+            MaybeReady::Blocking(spawn_blocking(move || {
                 std::net::ToSocketAddrs::to_socket_addrs(&(&host[..], port))
             }))
         }

tokio/src/net/mod.rs

@@ -1,3 +1,5 @@
+#![cfg(not(loom))]
+
 //! TCP/UDP/Unix bindings for `tokio`.
 //!
 //! This module contains the TCP/UDP/Unix networking types, similar to the standard

tokio/src/park/either.rs

@@ -0,0 +1,65 @@
+use crate::park::{Park, Unpark};
+
+use std::fmt;
+use std::time::Duration;
+
+pub(crate) enum Either<A, B> {
+    A(A),
+    B(B),
+}
+
+impl<A, B> Park for Either<A, B>
+where
+    A: Park,
+    B: Park,
+{
+    type Unpark = Either<A::Unpark, B::Unpark>;
+    type Error = Either<A::Error, B::Error>;
+
+    fn unpark(&self) -> Self::Unpark {
+        match self {
+            Either::A(a) => Either::A(a.unpark()),
+            Either::B(b) => Either::B(b.unpark()),
+        }
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        match self {
+            Either::A(a) => a.park().map_err(Either::A),
+            Either::B(b) => b.park().map_err(Either::B),
+        }
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        match self {
+            Either::A(a) => a.park_timeout(duration).map_err(Either::A),
+            Either::B(b) => b.park_timeout(duration).map_err(Either::B),
+        }
+    }
+}
+
+impl<A, B> Unpark for Either<A, B>
+where
+    A: Unpark,
+    B: Unpark,
+{
+    fn unpark(&self) {
+        match self {
+            Either::A(a) => a.unpark(),
+            Either::B(b) => b.unpark(),
+        }
+    }
+}
+
+impl<A, B> fmt::Debug for Either<A, B>
+where
+    A: fmt::Debug,
+    B: fmt::Debug,
+{
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Either::A(a) => a.fmt(fmt),
+            Either::B(b) => b.fmt(fmt),
+        }
+    }
+}

tokio/src/runtime/park/mod.rs → tokio/src/park/mod.rs

@@ -44,12 +44,18 @@
 //! [up]: trait.Unpark.html
 //! [mio]: https://docs.rs/mio/0.6/mio/struct.Poll.html
 
+cfg_resource_drivers! {
+    mod either;
+    pub(crate) use self::either::Either;
+}
+
 mod thread;
-#[cfg(feature = "rt-threaded")]
-pub(crate) use self::thread::CachedParkThread;
-#[cfg(not(feature = "io-driver"))]
 pub(crate) use self::thread::ParkThread;
 
+cfg_blocking_impl! {
+    pub(crate) use self::thread::CachedParkThread;
+}
+
 use std::sync::Arc;
 use std::time::Duration;
 
@@ -58,7 +64,7 @@ use std::time::Duration;
 /// See [module documentation][mod] for more details.
 ///
 /// [mod]: ../index.html
-pub trait Park {
+pub(crate) trait Park {
     /// Unpark handle type for the `Park` implementation.
     type Unpark: Unpark;
 
@@ -112,7 +118,7 @@ pub trait Park {
 ///
 /// [mod]: ../index.html
 /// [`Park`]: trait.Park.html
-pub trait Unpark: Sync + Send + 'static {
+pub(crate) trait Unpark: Sync + Send + 'static {
     /// Unblock a thread that is blocked by the associated `Park` handle.
     ///
     /// Calling `unpark` atomically makes available the unpark token, if it is