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diff --git a/third_party/rust/parking_lot/src/remutex.rs b/third_party/rust/parking_lot/src/remutex.rs
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+++ b/third_party/rust/parking_lot/src/remutex.rs
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+// Copyright 2016 Amanieu d'Antras
+//
+// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
+// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
+// http://opensource.org/licenses/MIT>, at your option. This file may not be
+// copied, modified, or distributed except according to those terms.
+
+use crate::raw_mutex::RawMutex;
+use core::num::NonZeroUsize;
+use lock_api::{self, GetThreadId};
+
+/// Implementation of the `GetThreadId` trait for `lock_api::ReentrantMutex`.
+pub struct RawThreadId;
+
+unsafe impl GetThreadId for RawThreadId {
+    const INIT: RawThreadId = RawThreadId;
+
+    fn nonzero_thread_id(&self) -> NonZeroUsize {
+        // The address of a thread-local variable is guaranteed to be unique to the
+        // current thread, and is also guaranteed to be non-zero. The variable has to have a
+        // non-zero size to guarantee it has a unique address for each thread.
+        thread_local!(static KEY: u8 = 0);
+        KEY.with(|x| {
+            NonZeroUsize::new(x as *const _ as usize)
+                .expect("thread-local variable address is null")
+        })
+    }
+}
+
+/// A mutex which can be recursively locked by a single thread.
+///
+/// This type is identical to `Mutex` except for the following points:
+///
+/// - Locking multiple times from the same thread will work correctly instead of
+///   deadlocking.
+/// - `ReentrantMutexGuard` does not give mutable references to the locked data.
+///   Use a `RefCell` if you need this.
+///
+/// See [`Mutex`](type.Mutex.html) for more details about the underlying mutex
+/// primitive.
+pub type ReentrantMutex<T> = lock_api::ReentrantMutex<RawMutex, RawThreadId, T>;
+
+/// Creates a new reentrant mutex in an unlocked state ready for use.
+///
+/// This allows creating a reentrant mutex in a constant context on stable Rust.
+pub const fn const_reentrant_mutex<T>(val: T) -> ReentrantMutex<T> {
+    ReentrantMutex::const_new(
+        <RawMutex as lock_api::RawMutex>::INIT,
+        <RawThreadId as lock_api::GetThreadId>::INIT,
+        val,
+    )
+}
+
+/// An RAII implementation of a "scoped lock" of a reentrant mutex. When this structure
+/// is dropped (falls out of scope), the lock will be unlocked.
+///
+/// The data protected by the mutex can be accessed through this guard via its
+/// `Deref` implementation.
+pub type ReentrantMutexGuard<'a, T> = lock_api::ReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
+
+/// An RAII mutex guard returned by `ReentrantMutexGuard::map`, which can point to a
+/// subfield of the protected data.
+///
+/// The main difference between `MappedReentrantMutexGuard` and `ReentrantMutexGuard` is that the
+/// former doesn't support temporarily unlocking and re-locking, since that
+/// could introduce soundness issues if the locked object is modified by another
+/// thread.
+pub type MappedReentrantMutexGuard<'a, T> =
+    lock_api::MappedReentrantMutexGuard<'a, RawMutex, RawThreadId, T>;
+
+#[cfg(test)]
+mod tests {
+    use crate::ReentrantMutex;
+    use std::cell::RefCell;
+    use std::sync::Arc;
+    use std::thread;
+
+    #[cfg(feature = "serde")]
+    use bincode::{deserialize, serialize};
+
+    #[test]
+    fn smoke() {
+        let m = ReentrantMutex::new(2);
+        {
+            let a = m.lock();
+            {
+                let b = m.lock();
+                {
+                    let c = m.lock();
+                    assert_eq!(*c, 2);
+                }
+                assert_eq!(*b, 2);
+            }
+            assert_eq!(*a, 2);
+        }
+    }
+
+    #[test]
+    fn is_mutex() {
+        let m = Arc::new(ReentrantMutex::new(RefCell::new(0)));
+        let m2 = m.clone();
+        let lock = m.lock();
+        let child = thread::spawn(move || {
+            let lock = m2.lock();
+            assert_eq!(*lock.borrow(), 4950);
+        });
+        for i in 0..100 {
+            let lock = m.lock();
+            *lock.borrow_mut() += i;
+        }
+        drop(lock);
+        child.join().unwrap();
+    }
+
+    #[test]
+    fn trylock_works() {
+        let m = Arc::new(ReentrantMutex::new(()));
+        let m2 = m.clone();
+        let _lock = m.try_lock();
+        let _lock2 = m.try_lock();
+        thread::spawn(move || {
+            let lock = m2.try_lock();
+            assert!(lock.is_none());
+        })
+        .join()
+        .unwrap();
+        let _lock3 = m.try_lock();
+    }
+
+    #[test]
+    fn test_reentrant_mutex_debug() {
+        let mutex = ReentrantMutex::new(vec![0u8, 10]);
+
+        assert_eq!(format!("{:?}", mutex), "ReentrantMutex { data: [0, 10] }");
+    }
+
+    #[cfg(feature = "serde")]
+    #[test]
+    fn test_serde() {
+        let contents: Vec<u8> = vec![0, 1, 2];
+        let mutex = ReentrantMutex::new(contents.clone());
+
+        let serialized = serialize(&mutex).unwrap();
+        let deserialized: ReentrantMutex<Vec<u8>> = deserialize(&serialized).unwrap();
+
+        assert_eq!(*(mutex.lock()), *(deserialized.lock()));
+        assert_eq!(contents, *(deserialized.lock()));
+    }
+}