rt: move park logic into runtime module (#5158)

The runtime is the primary user of parking. Moving park into runtime
will help future cleanups around combining context entering w/ block_on
calls.

tokio/src/future/block_on.rs

@@ -11,7 +11,7 @@ cfg_rt! {
 cfg_not_rt! {
     #[track_caller]
     pub(crate) fn block_on<F: Future>(f: F) -> F::Output {
-        let mut park = crate::park::thread::CachedParkThread::new();
+        let mut park = crate::runtime::park::CachedParkThread::new();
         park.block_on(f).unwrap()
     }
 }

tokio/src/lib.rs

@@ -479,7 +479,6 @@ pub mod io;
 pub mod net;
 
 mod loom;
-mod park;
 
 cfg_process! {
     pub mod process;

tokio/src/runtime/driver.rs

@@ -4,7 +4,7 @@
 // don't need to worry much about dead code with certain feature permutations.
 #![cfg_attr(not(feature = "full"), allow(dead_code))]
 
-use crate::park::thread::{ParkThread, UnparkThread};
+use crate::runtime::park::{ParkThread, UnparkThread};
 
 use std::io;
 use std::time::Duration;

tokio/src/runtime/enter.rs

@@ -146,7 +146,7 @@ cfg_rt! {
         where
             F: std::future::Future,
         {
-            use crate::park::thread::CachedParkThread;
+            use crate::runtime::park::CachedParkThread;
 
             let mut park = CachedParkThread::new();
             park.block_on(f)
@@ -160,7 +160,7 @@ cfg_rt! {
         where
             F: std::future::Future,
         {
-            use crate::park::thread::CachedParkThread;
+            use crate::runtime::park::CachedParkThread;
             use std::task::Context;
             use std::task::Poll::Ready;
             use std::time::Instant;

tokio/src/runtime/mod.rs

@@ -181,6 +181,8 @@ pub(crate) mod context;
 
 pub(crate) mod coop;
 
+pub(crate) mod park;
+
 mod driver;
 
 pub(crate) mod scheduler;

tokio/src/sync/mpsc/chan.rs

@@ -2,7 +2,7 @@ use crate::loom::cell::UnsafeCell;
 use crate::loom::future::AtomicWaker;
 use crate::loom::sync::atomic::AtomicUsize;
 use crate::loom::sync::Arc;
-use crate::park::thread::CachedParkThread;
+use crate::runtime::park::CachedParkThread;
 use crate::sync::mpsc::error::TryRecvError;
 use crate::sync::mpsc::{bounded, list, unbounded};
 use crate::sync::notify::Notify;