rt: cleanup and simplify scheduler (scheduler v2.5) (#2273)

A refactor of the scheduler internals focusing on simplifying and
reducing unsafety. There are no fundamental logic changes.

* The state transitions of the core task component are refined and
reduced.
* `basic_scheduler` has most unsafety removed.
* `local_set` has most unsafety removed.
* `threaded_scheduler` limits most unsafety to its queue implementation.

3 files changed, 0 insertions, 29 deletions

diff --git a/tokio/src/loom/std/alloc.rs b/tokio/src/loom/std/alloc.rs
deleted file mode 100644
index 25b199b1..00000000
--- a/tokio/src/loom/std/alloc.rs
+++ /dev/null
@@ -1,18 +0,0 @@
-#[derive(Debug)]
-pub(crate) struct Track<T> {
-    value: T,
-}
-
-impl<T> Track<T> {
-    pub(crate) fn new(value: T) -> Track<T> {
-        Track { value }
-    }
-
-    pub(crate) fn get_mut(&mut self) -> &mut T {
-        &mut self.value
-    }
-
-    pub(crate) fn into_inner(self) -> T {
-        self.value
-    }
-}
diff --git a/tokio/src/loom/std/causal_cell.rs b/tokio/src/loom/std/causal_cell.rs
index c4917e5f..8300437a 100644
--- a/tokio/src/loom/std/causal_cell.rs
+++ b/tokio/src/loom/std/causal_cell.rs
@@ -18,15 +18,6 @@ impl<T> CausalCell<T> {
         f(self.0.get())
     }
 
-    pub(crate) fn with_unchecked<F, R>(&self, f: F) -> R
-    where
-        F: FnOnce(*const T) -> R,
-    {
-        f(self.0.get())
-    }
-
-    pub(crate) fn check(&self) {}
-
     pub(crate) fn with_deferred<F, R>(&self, f: F) -> (R, CausalCheck)
     where
         F: FnOnce(*const T) -> R,
diff --git a/tokio/src/loom/std/mod.rs b/tokio/src/loom/std/mod.rs
index e4bae357..a56d778a 100644
--- a/tokio/src/loom/std/mod.rs
+++ b/tokio/src/loom/std/mod.rs
@@ -5,8 +5,6 @@ mod atomic_u64;
 mod atomic_usize;
 mod causal_cell;
 
-pub(crate) mod alloc;
-
 pub(crate) mod cell {
     pub(crate) use super::causal_cell::{CausalCell, CausalCheck};
 }