1 files changed, 112 insertions, 0 deletions
diff --git a/third_party/rust/crossbeam-channel/src/utils.rs b/third_party/rust/crossbeam-channel/src/utils.rs
new file mode 100644
index 0000000000..3fe171b2e4
--- /dev/null
+++ b/third_party/rust/crossbeam-channel/src/utils.rs
@@ -0,0 +1,112 @@
+//! Miscellaneous utilities.
+
+use std::cell::{Cell, UnsafeCell};
+use std::num::Wrapping;
+use std::ops::{Deref, DerefMut};
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use crossbeam_utils::Backoff;
+
+/// Randomly shuffles a slice.
+pub fn shuffle<T>(v: &mut [T]) {
+    let len = v.len();
+    if len <= 1 {
+        return;
+    }
+
+    thread_local! {
+        static RNG: Cell<Wrapping<u32>> = Cell::new(Wrapping(1_406_868_647));
+    }
+
+    let _ = RNG.try_with(|rng| {
+        for i in 1..len {
+            // This is the 32-bit variant of Xorshift.
+            //
+            // Source: https://en.wikipedia.org/wiki/Xorshift
+            let mut x = rng.get();
+            x ^= x << 13;
+            x ^= x >> 17;
+            x ^= x << 5;
+            rng.set(x);
+
+            let x = x.0;
+            let n = i + 1;
+
+            // This is a fast alternative to `let j = x % n`.
+            //
+            // Author: Daniel Lemire
+            // Source: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
+            let j = ((x as u64).wrapping_mul(n as u64) >> 32) as u32 as usize;
+
+            v.swap(i, j);
+        }
+    });
+}
+
+/// Sleeps until the deadline, or forever if the deadline isn't specified.
+pub fn sleep_until(deadline: Option<Instant>) {
+    loop {
+        match deadline {
+            None => thread::sleep(Duration::from_secs(1000)),
+            Some(d) => {
+                let now = Instant::now();
+                if now >= d {
+                    break;
+                }
+                thread::sleep(d - now);
+            }
+        }
+    }
+}
+
+/// A simple spinlock.
+pub struct Spinlock<T> {
+    flag: AtomicBool,
+    value: UnsafeCell<T>,
+}
+
+impl<T> Spinlock<T> {
+    /// Returns a new spinlock initialized with `value`.
+    pub fn new(value: T) -> Spinlock<T> {
+        Spinlock {
+            flag: AtomicBool::new(false),
+            value: UnsafeCell::new(value),
+        }
+    }
+
+    /// Locks the spinlock.
+    pub fn lock(&self) -> SpinlockGuard<'_, T> {
+        let backoff = Backoff::new();
+        while self.flag.swap(true, Ordering::Acquire) {
+            backoff.snooze();
+        }
+        SpinlockGuard { parent: self }
+    }
+}
+
+/// A guard holding a spinlock locked.
+pub struct SpinlockGuard<'a, T> {
+    parent: &'a Spinlock<T>,
+}
+
+impl<T> Drop for SpinlockGuard<'_, T> {
+    fn drop(&mut self) {
+        self.parent.flag.store(false, Ordering::Release);
+    }
+}
+
+impl<T> Deref for SpinlockGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.parent.value.get() }
+    }
+}
+
+impl<T> DerefMut for SpinlockGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.parent.value.get() }
+    }
+}