From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Wed, 17 Apr 2024 14:02:58 +0200
Subject: Adding upstream version 1.64.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 vendor/tokio/src/runtime/task/stack.rs | 83 ++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 vendor/tokio/src/runtime/task/stack.rs

(limited to 'vendor/tokio/src/runtime/task/stack.rs')

diff --git a/vendor/tokio/src/runtime/task/stack.rs b/vendor/tokio/src/runtime/task/stack.rs
new file mode 100644
index 000000000..9dd8d3f43
--- /dev/null
+++ b/vendor/tokio/src/runtime/task/stack.rs
@@ -0,0 +1,83 @@
+use crate::loom::sync::atomic::AtomicPtr;
+use crate::runtime::task::{Header, Task};
+
+use std::marker::PhantomData;
+use std::ptr::{self, NonNull};
+use std::sync::atomic::Ordering::{Acquire, Relaxed, Release};
+
+/// Concurrent stack of tasks, used to pass ownership of a task from one worker
+/// to another.
+pub(crate) struct TransferStack<T: 'static> {
+    head: AtomicPtr<Header>,
+    _p: PhantomData<T>,
+}
+
+impl<T: 'static> TransferStack<T> {
+    pub(crate) fn new() -> TransferStack<T> {
+        TransferStack {
+            head: AtomicPtr::new(ptr::null_mut()),
+            _p: PhantomData,
+        }
+    }
+
+    pub(crate) fn push(&self, task: Task<T>) {
+        let task = task.into_raw();
+
+        // We don't care about any memory associated w/ setting the `head`
+        // field, just the current value.
+        //
+        // The compare-exchange creates a release sequence.
+        let mut curr = self.head.load(Relaxed);
+
+        loop {
+            unsafe {
+                task.as_ref()
+                    .stack_next
+                    .with_mut(|ptr| *ptr = NonNull::new(curr))
+            };
+
+            let res = self
+                .head
+                .compare_exchange(curr, task.as_ptr() as *mut _, Release, Relaxed);
+
+            match res {
+                Ok(_) => return,
+                Err(actual) => {
+                    curr = actual;
+                }
+            }
+        }
+    }
+
+    pub(crate) fn drain(&self) -> impl Iterator<Item = Task<T>> {
+        struct Iter<T: 'static>(Option<NonNull<Header>>, PhantomData<T>);
+
+        impl<T: 'static> Iterator for Iter<T> {
+            type Item = Task<T>;
+
+            fn next(&mut self) -> Option<Task<T>> {
+                let task = self.0?;
+
+                // Move the cursor forward
+                self.0 = unsafe { task.as_ref().stack_next.with(|ptr| *ptr) };
+
+                // Return the task
+                unsafe { Some(Task::from_raw(task)) }
+            }
+        }
+
+        impl<T: 'static> Drop for Iter<T> {
+            fn drop(&mut self) {
+                use std::process;
+
+                if self.0.is_some() {
+                    // we have bugs
+                    process::abort();
+                }
+            }
+        }
+
+        let ptr = self.head.swap(ptr::null_mut(), Acquire);
+        Iter(NonNull::new(ptr), PhantomData)
+    }
+}
-- 
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