1 files changed, 557 insertions, 0 deletions
diff --git a/third_party/rust/dashmap/src/lock.rs b/third_party/rust/dashmap/src/lock.rs
new file mode 100644
index 0000000000..d27b413185
--- /dev/null
+++ b/third_party/rust/dashmap/src/lock.rs
@@ -0,0 +1,557 @@
+use core::cell::UnsafeCell;
+use core::default::Default;
+use core::fmt;
+use core::marker::PhantomData;
+use core::mem;
+use core::ops::{Deref, DerefMut};
+use core::ptr::NonNull;
+use core::sync::atomic::{spin_loop_hint as cpu_relax, AtomicUsize, Ordering};
+
+pub struct RwLock<T: ?Sized> {
+    lock: AtomicUsize,
+    data: UnsafeCell<T>,
+}
+
+const READER: usize = 1 << 2;
+
+const UPGRADED: usize = 1 << 1;
+
+const WRITER: usize = 1;
+
+#[derive(Debug)]
+pub struct RwLockReadGuard<'a, T: 'a + ?Sized> {
+    lock: &'a AtomicUsize,
+    data: NonNull<T>,
+}
+
+unsafe impl<'a, T: Send> Send for RwLockReadGuard<'a, T> {}
+
+unsafe impl<'a, T: Sync> Sync for RwLockReadGuard<'a, T> {}
+
+#[derive(Debug)]
+pub struct RwLockWriteGuard<'a, T: 'a + ?Sized> {
+    lock: &'a AtomicUsize,
+    data: NonNull<T>,
+    #[doc(hidden)]
+    _invariant: PhantomData<&'a mut T>,
+}
+
+unsafe impl<'a, T: Send> Send for RwLockWriteGuard<'a, T> {}
+
+unsafe impl<'a, T: Sync> Sync for RwLockWriteGuard<'a, T> {}
+
+#[derive(Debug)]
+pub struct RwLockUpgradeableGuard<'a, T: 'a + ?Sized> {
+    lock: &'a AtomicUsize,
+    data: NonNull<T>,
+    #[doc(hidden)]
+    _invariant: PhantomData<&'a mut T>,
+}
+
+unsafe impl<T: ?Sized + Send> Send for RwLock<T> {}
+
+unsafe impl<T: ?Sized + Send + Sync> Sync for RwLock<T> {}
+
+impl<T> RwLock<T> {
+    pub const fn new(user_data: T) -> RwLock<T> {
+        RwLock {
+            lock: AtomicUsize::new(0),
+            data: UnsafeCell::new(user_data),
+        }
+    }
+
+    pub fn into_inner(self) -> T {
+        let RwLock { data, .. } = self;
+
+        data.into_inner()
+    }
+}
+
+impl<T: ?Sized> RwLock<T> {
+    pub fn read(&self) -> RwLockReadGuard<T> {
+        loop {
+            match self.try_read() {
+                Some(guard) => return guard,
+                None => cpu_relax(),
+            }
+        }
+    }
+
+    pub fn try_read(&self) -> Option<RwLockReadGuard<T>> {
+        let value = self.lock.fetch_add(READER, Ordering::Acquire);
+
+        // We check the UPGRADED bit here so that new readers are prevented when an UPGRADED lock is held.
+        // This helps reduce writer starvation.
+        if value & (WRITER | UPGRADED) != 0 {
+            // Lock is taken, undo.
+            self.lock.fetch_sub(READER, Ordering::Release);
+
+            None
+        } else {
+            Some(RwLockReadGuard {
+                lock: &self.lock,
+                data: unsafe { NonNull::new_unchecked(self.data.get()) },
+            })
+        }
+    }
+
+    /// # Safety
+    ///
+    /// This is only safe if the lock is currently locked in read mode and the number of readers is not 0.
+    pub unsafe fn force_read_decrement(&self) {
+        debug_assert!(self.lock.load(Ordering::Relaxed) & !WRITER > 0);
+
+        self.lock.fetch_sub(READER, Ordering::Release);
+    }
+
+    /// # Safety
+    ///
+    /// The lock must be locked in write mode.
+    pub unsafe fn force_write_unlock(&self) {
+        debug_assert_eq!(self.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED), 0);
+
+        self.lock.fetch_and(!(WRITER | UPGRADED), Ordering::Release);
+    }
+
+    fn try_write_internal(&self, strong: bool) -> Option<RwLockWriteGuard<T>> {
+        if compare_exchange(
+            &self.lock,
+            0,
+            WRITER,
+            Ordering::Acquire,
+            Ordering::Relaxed,
+            strong,
+        )
+        .is_ok()
+        {
+            Some(RwLockWriteGuard {
+                lock: &self.lock,
+                data: unsafe { NonNull::new_unchecked(self.data.get()) },
+                _invariant: PhantomData,
+            })
+        } else {
+            None
+        }
+    }
+
+    pub fn write(&self) -> RwLockWriteGuard<T> {
+        loop {
+            match self.try_write_internal(false) {
+                Some(guard) => return guard,
+                None => cpu_relax(),
+            }
+        }
+    }
+
+    pub fn try_write(&self) -> Option<RwLockWriteGuard<T>> {
+        self.try_write_internal(true)
+    }
+
+    pub fn upgradeable_read(&self) -> RwLockUpgradeableGuard<T> {
+        loop {
+            match self.try_upgradeable_read() {
+                Some(guard) => return guard,
+                None => cpu_relax(),
+            }
+        }
+    }
+
+    pub fn try_upgradeable_read(&self) -> Option<RwLockUpgradeableGuard<T>> {
+        if self.lock.fetch_or(UPGRADED, Ordering::Acquire) & (WRITER | UPGRADED) == 0 {
+            Some(RwLockUpgradeableGuard {
+                lock: &self.lock,
+                data: unsafe { NonNull::new_unchecked(self.data.get()) },
+                _invariant: PhantomData,
+            })
+        } else {
+            None
+        }
+    }
+
+    /// # Safety
+    /// Write locks may not be used in combination with this method.
+    pub unsafe fn get(&self) -> &T {
+        &*self.data.get()
+    }
+
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data.get() }
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for RwLock<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self.try_read() {
+            Some(guard) => write!(f, "RwLock {{ data: ")
+                .and_then(|()| (&*guard).fmt(f))
+                .and_then(|()| write!(f, "}}")),
+            None => write!(f, "RwLock {{ <locked> }}"),
+        }
+    }
+}
+
+impl<T: ?Sized + Default> Default for RwLock<T> {
+    fn default() -> RwLock<T> {
+        RwLock::new(Default::default())
+    }
+}
+
+impl<'rwlock, T: ?Sized> RwLockUpgradeableGuard<'rwlock, T> {
+    fn try_upgrade_internal(self, strong: bool) -> Result<RwLockWriteGuard<'rwlock, T>, Self> {
+        if compare_exchange(
+            &self.lock,
+            UPGRADED,
+            WRITER,
+            Ordering::Acquire,
+            Ordering::Relaxed,
+            strong,
+        )
+        .is_ok()
+        {
+            let out = Ok(RwLockWriteGuard {
+                lock: &self.lock,
+                data: self.data,
+                _invariant: PhantomData,
+            });
+
+            mem::forget(self);
+
+            out
+        } else {
+            Err(self)
+        }
+    }
+
+    pub fn upgrade(mut self) -> RwLockWriteGuard<'rwlock, T> {
+        loop {
+            self = match self.try_upgrade_internal(false) {
+                Ok(guard) => return guard,
+                Err(e) => e,
+            };
+
+            cpu_relax();
+        }
+    }
+
+    pub fn try_upgrade(self) -> Result<RwLockWriteGuard<'rwlock, T>, Self> {
+        self.try_upgrade_internal(true)
+    }
+
+    pub fn downgrade(self) -> RwLockReadGuard<'rwlock, T> {
+        self.lock.fetch_add(READER, Ordering::Acquire);
+
+        RwLockReadGuard {
+            lock: &self.lock,
+            data: self.data,
+        }
+    }
+}
+
+impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
+    pub fn downgrade(self) -> RwLockReadGuard<'rwlock, T> {
+        self.lock.fetch_add(READER, Ordering::Acquire);
+
+        RwLockReadGuard {
+            lock: &self.lock,
+            data: self.data,
+        }
+    }
+}
+
+impl<'rwlock, T: ?Sized> Deref for RwLockReadGuard<'rwlock, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { self.data.as_ref() }
+    }
+}
+
+impl<'rwlock, T: ?Sized> Deref for RwLockUpgradeableGuard<'rwlock, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { self.data.as_ref() }
+    }
+}
+
+impl<'rwlock, T: ?Sized> Deref for RwLockWriteGuard<'rwlock, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { self.data.as_ref() }
+    }
+}
+
+impl<'rwlock, T: ?Sized> DerefMut for RwLockWriteGuard<'rwlock, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { self.data.as_mut() }
+    }
+}
+
+impl<'rwlock, T: ?Sized> Drop for RwLockReadGuard<'rwlock, T> {
+    fn drop(&mut self) {
+        debug_assert!(self.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED) > 0);
+
+        self.lock.fetch_sub(READER, Ordering::Release);
+    }
+}
+
+impl<'rwlock, T: ?Sized> Drop for RwLockUpgradeableGuard<'rwlock, T> {
+    fn drop(&mut self) {
+        debug_assert_eq!(
+            self.lock.load(Ordering::Relaxed) & (WRITER | UPGRADED),
+            UPGRADED
+        );
+
+        self.lock.fetch_sub(UPGRADED, Ordering::AcqRel);
+    }
+}
+
+impl<'rwlock, T: ?Sized> Drop for RwLockWriteGuard<'rwlock, T> {
+    fn drop(&mut self) {
+        debug_assert_eq!(self.lock.load(Ordering::Relaxed) & WRITER, WRITER);
+
+        self.lock.fetch_and(!(WRITER | UPGRADED), Ordering::Release);
+    }
+}
+
+fn compare_exchange(
+    atomic: &AtomicUsize,
+    current: usize,
+    new: usize,
+    success: Ordering,
+    failure: Ordering,
+    strong: bool,
+) -> Result<usize, usize> {
+    if strong {
+        atomic.compare_exchange(current, new, success, failure)
+    } else {
+        atomic.compare_exchange_weak(current, new, success, failure)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::prelude::v1::*;
+    use std::sync::atomic::{AtomicUsize, Ordering};
+    use std::sync::mpsc::channel;
+    use std::sync::Arc;
+    use std::thread;
+
+    #[derive(Eq, PartialEq, Debug)]
+    struct NonCopy(i32);
+
+    #[test]
+    fn smoke() {
+        let l = RwLock::new(());
+        drop(l.read());
+        drop(l.write());
+        drop((l.read(), l.read()));
+        drop(l.write());
+    }
+
+    #[cfg(not(target_arch = "wasm32"))]
+    #[test]
+    fn test_rw_arc() {
+        let arc = Arc::new(RwLock::new(0));
+        let arc2 = arc.clone();
+        let (tx, rx) = channel();
+
+        thread::spawn(move || {
+            let mut lock = arc2.write();
+
+            for _ in 0..10 {
+                let tmp = *lock;
+                *lock = -1;
+                thread::yield_now();
+                *lock = tmp + 1;
+            }
+
+            tx.send(()).unwrap();
+        });
+
+        let mut children = Vec::new();
+
+        for _ in 0..5 {
+            let arc3 = arc.clone();
+
+            children.push(thread::spawn(move || {
+                let lock = arc3.read();
+                assert!(*lock >= 0);
+            }));
+        }
+
+        for r in children {
+            assert!(r.join().is_ok());
+        }
+
+        rx.recv().unwrap();
+        let lock = arc.read();
+        assert_eq!(*lock, 10);
+    }
+
+    #[cfg(not(target_arch = "wasm32"))]
+    #[test]
+    fn test_rw_access_in_unwind() {
+        let arc = Arc::new(RwLock::new(1));
+        let arc2 = arc.clone();
+
+        let _ = thread::spawn(move || {
+            struct Unwinder {
+                i: Arc<RwLock<isize>>,
+            }
+
+            impl Drop for Unwinder {
+                fn drop(&mut self) {
+                    let mut lock = self.i.write();
+
+                    *lock += 1;
+                }
+            }
+
+            let _u = Unwinder { i: arc2 };
+
+            panic!();
+        })
+        .join();
+
+        let lock = arc.read();
+        assert_eq!(*lock, 2);
+    }
+
+    #[test]
+    fn test_rwlock_unsized() {
+        let rw: &RwLock<[i32]> = &RwLock::new([1, 2, 3]);
+
+        {
+            let b = &mut *rw.write();
+            b[0] = 4;
+            b[2] = 5;
+        }
+
+        let comp: &[i32] = &[4, 2, 5];
+
+        assert_eq!(&*rw.read(), comp);
+    }
+
+    #[test]
+    fn test_rwlock_try_write() {
+        use std::mem::drop;
+
+        let lock = RwLock::new(0isize);
+        let read_guard = lock.read();
+        let write_result = lock.try_write();
+
+        match write_result {
+            None => (),
+            Some(_) => panic!("try_write should not succeed while read_guard is in scope"),
+        }
+
+        drop(read_guard);
+    }
+
+    #[test]
+    fn test_rw_try_read() {
+        let m = RwLock::new(0);
+
+        mem::forget(m.write());
+
+        assert!(m.try_read().is_none());
+    }
+
+    #[test]
+    fn test_into_inner() {
+        let m = RwLock::new(NonCopy(10));
+
+        assert_eq!(m.into_inner(), NonCopy(10));
+    }
+
+    #[test]
+    fn test_into_inner_drop() {
+        struct Foo(Arc<AtomicUsize>);
+
+        impl Drop for Foo {
+            fn drop(&mut self) {
+                self.0.fetch_add(1, Ordering::SeqCst);
+            }
+        }
+
+        let num_drops = Arc::new(AtomicUsize::new(0));
+        let m = RwLock::new(Foo(num_drops.clone()));
+        assert_eq!(num_drops.load(Ordering::SeqCst), 0);
+
+        {
+            let _inner = m.into_inner();
+            assert_eq!(num_drops.load(Ordering::SeqCst), 0);
+        }
+
+        assert_eq!(num_drops.load(Ordering::SeqCst), 1);
+    }
+
+    #[test]
+    fn test_force_read_decrement() {
+        let m = RwLock::new(());
+        ::std::mem::forget(m.read());
+        ::std::mem::forget(m.read());
+        ::std::mem::forget(m.read());
+        assert!(m.try_write().is_none());
+
+        unsafe {
+            m.force_read_decrement();
+            m.force_read_decrement();
+        }
+
+        assert!(m.try_write().is_none());
+
+        unsafe {
+            m.force_read_decrement();
+        }
+
+        assert!(m.try_write().is_some());
+    }
+
+    #[test]
+    fn test_force_write_unlock() {
+        let m = RwLock::new(());
+
+        ::std::mem::forget(m.write());
+
+        assert!(m.try_read().is_none());
+
+        unsafe {
+            m.force_write_unlock();
+        }
+
+        assert!(m.try_read().is_some());
+    }
+
+    #[test]
+    fn test_upgrade_downgrade() {
+        let m = RwLock::new(());
+
+        {
+            let _r = m.read();
+            let upg = m.try_upgradeable_read().unwrap();
+            assert!(m.try_read().is_none());
+            assert!(m.try_write().is_none());
+            assert!(upg.try_upgrade().is_err());
+        }
+
+        {
+            let w = m.write();
+            assert!(m.try_upgradeable_read().is_none());
+            let _r = w.downgrade();
+            assert!(m.try_upgradeable_read().is_some());
+            assert!(m.try_read().is_some());
+            assert!(m.try_write().is_none());
+        }
+
+        {
+            let _u = m.upgradeable_read();
+            assert!(m.try_upgradeable_read().is_none());
+        }
+
+        assert!(m.try_upgradeable_read().unwrap().try_upgrade().is_ok());
+    }
+}