rt: coalesce thread-locals used by the runtime (#1925)

Previously, thread-locals used by the various drivers were situated
with the driver code. This resulted in state being spread out and many
thread-locals being required to run a runtime.

This PR coalesces the thread-locals into a single struct.

2 files changed, 3 insertions, 47 deletions

diff --git a/tokio/src/time/driver/handle.rs b/tokio/src/time/driver/handle.rs
index 7d21ad0d..6a8fe2bb 100644
--- a/tokio/src/time/driver/handle.rs
+++ b/tokio/src/time/driver/handle.rs
@@ -1,7 +1,6 @@
+use crate::runtime::context;
 use crate::time::driver::Inner;
-use std::cell::RefCell;
 use std::fmt;
-use std::marker::PhantomData;
 use std::sync::{Arc, Weak};
 
 /// Handle to time driver instance.
@@ -10,46 +9,6 @@ pub(crate) struct Handle {
     inner: Weak<Inner>,
 }
 
-thread_local! {
-    /// Tracks the timer for the current execution context.
-    static CURRENT_TIMER: RefCell<Option<Handle>> = RefCell::new(None)
-}
-
-#[derive(Debug)]
-/// Guard that unsets the current default timer on drop.
-pub(crate) struct DefaultGuard<'a> {
-    prev: Option<Handle>,
-    _lifetime: PhantomData<&'a u8>,
-}
-
-impl Drop for DefaultGuard<'_> {
-    fn drop(&mut self) {
-        CURRENT_TIMER.with(|current| {
-            let mut current = current.borrow_mut();
-            *current = self.prev.take();
-        })
-    }
-}
-
-/// Sets handle to default timer, returning guard that unsets it on drop.
-///
-/// # Panics
-///
-/// This function panics if there already is a default timer set.
-pub(crate) fn set_default(handle: &Handle) -> DefaultGuard<'_> {
-    CURRENT_TIMER.with(|current| {
-        let mut current = current.borrow_mut();
-        let prev = current.take();
-
-        *current = Some(handle.clone());
-
-        DefaultGuard {
-            prev,
-            _lifetime: PhantomData,
-        }
-    })
-}
-
 impl Handle {
     /// Create a new timer `Handle` from a shared `Inner` timer state.
     pub(crate) fn new(inner: Weak<Inner>) -> Self {
@@ -62,10 +21,7 @@ impl Handle {
     ///
     /// This function panics if there is no current timer set.
     pub(crate) fn current() -> Self {
-        CURRENT_TIMER.with(|current| match *current.borrow() {
-            Some(ref handle) => handle.clone(),
-            None => panic!("no current timer"),
-        })
+        context::ThreadContext::time_handle().expect("no current timer")
     }
 
     /// Try to return a strong ref to the inner
diff --git a/tokio/src/time/driver/mod.rs b/tokio/src/time/driver/mod.rs
index 5d487423..605d9bca 100644
--- a/tokio/src/time/driver/mod.rs
+++ b/tokio/src/time/driver/mod.rs
@@ -7,7 +7,7 @@ mod entry;
 use self::entry::Entry;
 
 mod handle;
-pub(crate) use self::handle::{set_default, Handle};
+pub(crate) use self::handle::Handle;
 
 mod registration;
 pub(crate) use self::registration::Registration;