From a22426916ddf2f0b7927f31b7b7a8358f3e4827d Mon Sep 17 00:00:00 2001
From: Ibraheem Ahmed <ibraheem@ibraheem.ca>
Date: Sat, 12 Nov 2022 23:13:58 -0500
Subject: [PATCH] avoid calling `thread::current` in channel destructor

---
 library/std/src/sync/mpmc/context.rs |  9 +++++----
 library/std/src/sync/mpmc/waker.rs   | 15 ++++++---------
 2 files changed, 11 insertions(+), 13 deletions(-)

diff --git a/library/std/src/sync/mpmc/context.rs b/library/std/src/sync/mpmc/context.rs
index 3077c0ee375..bbfc6ce00ff 100644
--- a/library/std/src/sync/mpmc/context.rs
+++ b/library/std/src/sync/mpmc/context.rs
@@ -1,12 +1,13 @@
 //! Thread-local channel context.
 
 use super::select::Selected;
+use super::waker::current_thread_id;
 
 use crate::cell::Cell;
 use crate::ptr;
 use crate::sync::atomic::{AtomicPtr, AtomicUsize, Ordering};
 use crate::sync::Arc;
-use crate::thread::{self, Thread, ThreadId};
+use crate::thread::{self, Thread};
 use crate::time::Instant;
 
 /// Thread-local context.
@@ -28,7 +29,7 @@ struct Inner {
     thread: Thread,
 
     /// Thread id.
-    thread_id: ThreadId,
+    thread_id: usize,
 }
 
 impl Context {
@@ -70,7 +71,7 @@ impl Context {
                 select: AtomicUsize::new(Selected::Waiting.into()),
                 packet: AtomicPtr::new(ptr::null_mut()),
                 thread: thread::current(),
-                thread_id: thread::current().id(),
+                thread_id: current_thread_id(),
             }),
         }
     }
@@ -148,7 +149,7 @@ impl Context {
 
     /// Returns the id of the thread this context belongs to.
     #[inline]
-    pub fn thread_id(&self) -> ThreadId {
+    pub fn thread_id(&self) -> usize {
         self.inner.thread_id
     }
 }
diff --git a/library/std/src/sync/mpmc/waker.rs b/library/std/src/sync/mpmc/waker.rs
index 572ac01d3f7..4912ca4f815 100644
--- a/library/std/src/sync/mpmc/waker.rs
+++ b/library/std/src/sync/mpmc/waker.rs
@@ -6,7 +6,6 @@ use super::select::{Operation, Selected};
 use crate::ptr;
 use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sync::Mutex;
-use crate::thread::{self, ThreadId};
 
 /// Represents a thread blocked on a specific channel operation.
 pub(crate) struct Entry {
@@ -195,13 +194,11 @@ impl Drop for SyncWaker {
     }
 }
 
-/// Returns the id of the current thread.
+/// Returns a unique id for the current thread.
 #[inline]
-fn current_thread_id() -> ThreadId {
-    thread_local! {
-        /// Cached thread-local id.
-        static THREAD_ID: ThreadId = thread::current().id();
-    }
-
-    THREAD_ID.try_with(|id| *id).unwrap_or_else(|_| thread::current().id())
+pub fn current_thread_id() -> usize {
+    // `u8` is not drop so this variable will be available during thread destruction,
+    // whereas `thread::current()` would not be
+    thread_local! { static DUMMY: u8 = 0 }
+    DUMMY.with(|x| (x as *const u8).addr())
 }