spin-sync 0.3.2

Synchronization primitives using spinlock. The interface resembles std::sync. The constructors of public structs are const; i.e. it is possible to declare static Mutex<T> as long as T can be build statically.
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</pre><div class="example-wrap"><pre class="rust ">
<span class="comment">// Copyright 2020 Shin Yoshida</span>
<span class="comment">//</span>
<span class="comment">// &quot;LGPL-3.0-or-later OR Apache-2.0 OR BSD-2-Clause&quot;</span>
<span class="comment">//</span>
<span class="comment">// This is part of spin-sync</span>
<span class="comment">//</span>
<span class="comment">//  spin-sync is free software: you can redistribute it and/or modify</span>
<span class="comment">//  it under the terms of the GNU Lesser General Public License as published by</span>
<span class="comment">//  the Free Software Foundation, either version 3 of the License, or</span>
<span class="comment">//  (at your option) any later version.</span>
<span class="comment">//</span>
<span class="comment">//  spin-sync is distributed in the hope that it will be useful,</span>
<span class="comment">//  but WITHOUT ANY WARRANTY; without even the implied warranty of</span>
<span class="comment">//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the</span>
<span class="comment">//  GNU Lesser General Public License for more details.</span>
<span class="comment">//</span>
<span class="comment">//  You should have received a copy of the GNU Lesser General Public License</span>
<span class="comment">//  along with spin-sync.  If not, see &lt;http://www.gnu.org/licenses/&gt;.</span>
<span class="comment">//</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 (the &quot;License&quot;);</span>
<span class="comment">// you may not use this file except in compliance with the License.</span>
<span class="comment">// You may obtain a copy of the License at</span>
<span class="comment">//</span>
<span class="comment">//     http://www.apache.org/licenses/LICENSE-2.0</span>
<span class="comment">//</span>
<span class="comment">// Unless required by applicable law or agreed to in writing, software</span>
<span class="comment">// distributed under the License is distributed on an &quot;AS IS&quot; BASIS,</span>
<span class="comment">// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</span>
<span class="comment">// See the License for the specific language governing permissions and</span>
<span class="comment">// limitations under the License.</span>
<span class="comment">//</span>
<span class="comment">//</span>
<span class="comment">// Redistribution and use in source and binary forms, with or without modification, are permitted</span>
<span class="comment">// provided that the following conditions are met:</span>
<span class="comment">//</span>
<span class="comment">// 1. Redistributions of source code must retain the above copyright notice, this list of</span>
<span class="comment">//    conditions and the following disclaimer.</span>
<span class="comment">// 2. Redistributions in binary form must reproduce the above copyright notice, this</span>
<span class="comment">//    list of conditions and the following disclaimer in the documentation and/or other</span>
<span class="comment">//    materials provided with the distribution.</span>
<span class="comment">//</span>
<span class="comment">// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS &quot;AS IS&quot; AND</span>
<span class="comment">// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED</span>
<span class="comment">// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.</span>
<span class="comment">// IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,</span>
<span class="comment">// INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT</span>
<span class="comment">// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR</span>
<span class="comment">// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,</span>
<span class="comment">// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)</span>
<span class="comment">// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE</span>
<span class="comment">// POSSIBILITY OF SUCH DAMAGE.</span>

<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">UnsafeCell</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ops</span>::{<span class="ident">Deref</span>, <span class="ident">DerefMut</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">panic</span>::{<span class="ident">RefUnwindSafe</span>, <span class="ident">UnwindSafe</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicU64</span>, <span class="ident">Ordering</span>};

<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">misc</span>::{<span class="ident">PhantomRwLock</span>, <span class="ident">PhantomRwLockReadGuard</span>, <span class="ident">PhantomRwLockWriteGuard</span>};
<span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">result</span>::{<span class="ident">LockResult</span>, <span class="ident">PoisonError</span>, <span class="ident">TryLockError</span>, <span class="ident">TryLockResult</span>};

<span class="doccomment">/// A reader-writer lock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// It behaves like std::sync::RwLock except for using spinlock.</span>
<span class="doccomment">/// What is more, the constructor is a const function; i.e. it is possible to declare</span>
<span class="doccomment">/// `static RwLock&lt;T&gt;` variable as long as the inner data can be built statically.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This type of lock allows either a number of readers or at most one writer</span>
<span class="doccomment">/// at the same time. Readers are allowed read-only access (shared access)</span>
<span class="doccomment">/// to the underlying data while the writer is allowed read/write access</span>
<span class="doccomment">/// (exclusive access.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In comparison, a [`Mutex`] does not distinguish between readers and writers,</span>
<span class="doccomment">/// therefore blocking any threads waiting for the lock to become available.</span>
<span class="doccomment">/// An `RwLock` will allow any number of readers to acquire the lock as long as</span>
<span class="doccomment">/// a writer is not holding the lock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// There is no priority difference with respect to the ordering of</span>
<span class="doccomment">/// whether contentious readers or writers will acquire the lock first.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Poisoning</span>
<span class="doccomment">///</span>
<span class="doccomment">/// An `RwLock`, like [`Mutex`], will become poisoned on a panic. Note, however,</span>
<span class="doccomment">/// that an `RwLock` may only be poisoned if a panic occurs while it is locked</span>
<span class="doccomment">/// exclusively (write mode). If a panic occurs in any reader, then the lock</span>
<span class="doccomment">/// will not be poisoned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Mutex`]: struct.Mutex.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Create a variable protected by a RwLock, increment it by 2 in worker threads</span>
<span class="doccomment">/// at the same time, and check the variable was updated rightly.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use spin_sync::RwLock;</span>
<span class="doccomment">/// use std::sync::Arc;</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// const WORKER_NUM: usize = 10;</span>
<span class="doccomment">/// let mut handles = Vec::with_capacity(WORKER_NUM);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // We can declare static RwLock&lt;usize&gt; variable because RwLock::new is a const function.</span>
<span class="doccomment">/// static RWLOCK: RwLock&lt;usize&gt; = RwLock::new(0);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Create worker threads to inclement the value by 2.</span>
<span class="doccomment">/// for _ in 0..WORKER_NUM {</span>
<span class="doccomment">///     let handle = thread::spawn(move || {</span>
<span class="doccomment">///         let mut num = RWLOCK.write().unwrap();</span>
<span class="doccomment">///         *num += 2;</span>
<span class="doccomment">///     });</span>
<span class="doccomment">///</span>
<span class="doccomment">///     handles.push(handle);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Make sure the value is always multipile of 2 even if some worker threads</span>
<span class="doccomment">/// // are working.</span>
<span class="doccomment">/// //</span>
<span class="doccomment">/// // Enclosing the lock with `{}` to drop it before waiting for the worker</span>
<span class="doccomment">/// // threads; otherwise, deadlocks could be occurred.</span>
<span class="doccomment">/// {</span>
<span class="doccomment">///     let num = RWLOCK.read().unwrap();</span>
<span class="doccomment">///     assert_eq!(0, *num % 2);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Wait for the all worker threads are finished.</span>
<span class="doccomment">/// for handle in handles {</span>
<span class="doccomment">///     handle.join().unwrap();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Make sure the value is incremented by 2 times the worker count.</span>
<span class="doccomment">/// let num = RWLOCK.read().unwrap();</span>
<span class="doccomment">/// assert_eq!(2 * WORKER_NUM, *num);</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> {
    <span class="comment">// Each bit represents as follows.</span>
    <span class="comment">// - The most significant bit: poison flag</span>
    <span class="comment">// - The 2nd most significant bit: exclusive write lock flag</span>
    <span class="comment">// - The others: shared read lock count</span>
    <span class="comment">// Use helper functions for lock state.</span>
    <span class="ident">lock</span>: <span class="ident">AtomicU64</span>,

    <span class="ident">_phantom</span>: <span class="ident">PhantomRwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>,
    <span class="ident">data</span>: <span class="ident">UnsafeCell</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>,
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Creates a new instance in unlocked state ready for use.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Declare as a static variable.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// static LOCK: RwLock&lt;i32&gt; = RwLock::new(5);</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Declare as a local variable.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let lock = RwLock::new(5);</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">const</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="self">Self</span> {
        <span class="self">Self</span> {
            <span class="ident">lock</span>: <span class="ident">AtomicU64</span>::<span class="ident">new</span>(<span class="ident">INIT</span>),
            <span class="ident">data</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">t</span>),
            <span class="ident">_phantom</span>: <span class="ident">PhantomRwLock</span> {},
        }
    }

    <span class="doccomment">/// Consumes this instance and returns the underlying data.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Note that this method won&#39;t acquire any lock because we know there is</span>
    <span class="doccomment">/// no other references to `self`.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Errors</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If another user panicked while holding the exclusive write lock of this instance,</span>
    <span class="doccomment">/// this method call wraps the guard in an error and returns it.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let rwlock = RwLock::new(0);</span>
    <span class="doccomment">/// assert_eq!(0, rwlock.into_inner().unwrap());</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_inner</span>(<span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockResult</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {
        <span class="comment">// We know statically that there are no outstanding references to</span>
        <span class="comment">// `self` so there&#39;s no need to lock the inner lock.</span>
        <span class="kw">let</span> <span class="ident">is_err</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">is_poisoned</span>();
        <span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">data</span>.<span class="ident">into_inner</span>();

        <span class="kw">if</span> <span class="ident">is_err</span> {
            <span class="prelude-val">Err</span>(<span class="ident">PoisonError</span>::<span class="ident">new</span>(<span class="ident">data</span>))
        } <span class="kw">else</span> {
            <span class="prelude-val">Ok</span>(<span class="ident">data</span>)
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {
    <span class="doccomment">/// The maximum shared read locks of each instance.</span>
    <span class="kw">pub</span> <span class="kw">const</span> <span class="ident">MAX_READ_LOCK_COUNT</span>: <span class="ident">u64</span> <span class="op">=</span> <span class="ident">SHARED_LOCK_MASK</span>;

    <span class="doccomment">/// Blocks the current thread until acquiring a shared read lock, and</span>
    <span class="doccomment">/// returns an RAII guard object.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The actual flow will be as follows.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// 1. User calls this method.</span>
    <span class="doccomment">///    1. Blocks until this thread acquires a shared read lock</span>
    <span class="doccomment">///       (i.e. until the exclusive write lock is held.)</span>
    <span class="doccomment">///    1. Creates an RAII guard object.</span>
    <span class="doccomment">///    1. Wrapps the guard in `Result` and returns it. If this instance has been</span>
    <span class="doccomment">///       poisoned, it is wrapped in an `Err`; otherwise wrapped in an `Ok`.</span>
    <span class="doccomment">/// 1. User accesses to the underlying data to read through the guard.</span>
    <span class="doccomment">///    (No write access is then.)</span>
    <span class="doccomment">/// 1. The guard is dropped (falls out of scope) and the lock is released.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Errors</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If another user panicked while holding the exclusive write lock of this instance,</span>
    <span class="doccomment">/// this method call wraps the guard in an error and returns it.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Panics</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// This method panics if `MAX_READ_LOCK_COUNT` shared locks are.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let lock = RwLock::new(1);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let guard1 = lock.read().unwrap();</span>
    <span class="doccomment">/// assert_eq!(1, *guard1);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let guard2 = lock.read().unwrap();</span>
    <span class="doccomment">/// assert_eq!(1, *guard2);</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockResult</span><span class="op">&lt;</span><span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span><span class="op">&gt;</span> {
        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_lock</span>(<span class="ident">acquire_shared_lock</span>, <span class="ident">is_locked_exclusively</span>) {
                <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_locked_exclusively</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="ident">std</span>::<span class="ident">thread</span>::<span class="ident">yield_now</span>(),
                <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_poisoned</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">PoisonError</span>::<span class="ident">new</span>(<span class="ident">RwLockReadGuard</span>::<span class="ident">new</span>(<span class="self">self</span>))),
                <span class="kw">_</span> <span class="op">=</span><span class="op">&gt;</span> <span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">RwLockReadGuard</span>::<span class="ident">new</span>(<span class="self">self</span>)),
            }
        }
    }

    <span class="doccomment">/// Attempts to acquire a shared read lock and returns an RAII guard object if succeeded.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Behaves like [`read`] except for this method returns an error immediately</span>
    <span class="doccomment">/// if the exclusive write lock is being held.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// This function does not block.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The actual flow will be as follows.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// 1. User calls this method.</span>
    <span class="doccomment">///    1. Tries to acquire a shared read lock. If failed (i.e. if the exclusive write</span>
    <span class="doccomment">///       lock is being held,) returns an error immediately and this flow is finished here.</span>
    <span class="doccomment">///    1. Creates an RAII guard object.</span>
    <span class="doccomment">///    1. Wrapps the guard in `Result` and returns it. If this instance has been poisoned,</span>
    <span class="doccomment">///       it is wrapped in an `Err`; otherwise wrapped in an `Ok`.</span>
    <span class="doccomment">/// 1. User accesses to the underlying data to read through the guard.</span>
    <span class="doccomment">///    (No write access is at then.)</span>
    <span class="doccomment">/// 1. The guard is dropped (falls out of scope) and the lock is released.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`read`]: #method.read</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Panics</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// This method panics if `MAX_READ_LOCK` shared read locks are.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Errors</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// - If another user is holding the exclusive write lock,</span>
    <span class="doccomment">///   [`TryLockError::WouldBlock`] is returned.</span>
    <span class="doccomment">/// - If this method call succeeded to acquire a shared read lock, and if another</span>
    <span class="doccomment">///   user had panicked while holding the exclusive write lock,</span>
    <span class="doccomment">///   [`TryLockError::Poisoned`] is returned.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`TryLockError::WouldBlock`]: type.TryLockError.html</span>
    <span class="doccomment">/// [`TryLockError::Poisoned`]: type.TryLockError.html</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let lock = RwLock::new(1);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let guard0 = lock.try_read().unwrap();</span>
    <span class="doccomment">/// assert_eq!(1, *guard0);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let guard1 = lock.try_read().unwrap();</span>
    <span class="doccomment">/// assert_eq!(1, *guard1);</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">try_read</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">TryLockResult</span><span class="op">&lt;</span><span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span><span class="op">&gt;</span> {
        <span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_lock</span>(<span class="ident">acquire_shared_lock</span>, <span class="ident">is_locked_exclusively</span>) {
            <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_locked_exclusively</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="prelude-val">Err</span>(<span class="ident">TryLockError</span>::<span class="ident">WouldBlock</span>),
            <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_poisoned</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="prelude-val">Err</span>(<span class="ident">TryLockError</span>::<span class="ident">Poisoned</span>(<span class="ident">PoisonError</span>::<span class="ident">new</span>(
                <span class="ident">RwLockReadGuard</span>::<span class="ident">new</span>(<span class="self">self</span>),
            ))),
            <span class="kw">_</span> <span class="op">=</span><span class="op">&gt;</span> <span class="prelude-val">Ok</span>(<span class="ident">RwLockReadGuard</span>::<span class="ident">new</span>(<span class="self">self</span>)),
        }
    }

    <span class="doccomment">/// Attempts to acquire the exclusive write lock and returns an RAII guard object</span>
    <span class="doccomment">/// if succeeded.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Behaves like [`write`] except for this method returns an error immediately</span>
    <span class="doccomment">/// if any other lock (either read lock or write lock) is being held.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// This method does not block.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The actual flow will be as follows.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// 1. User calls this method.</span>
    <span class="doccomment">///    1. Tries to acquire the exclusive write lock. If failed (i.e. if any other lock is</span>
    <span class="doccomment">///       being held,) returns an error immediately and this flow is finished here.</span>
    <span class="doccomment">///    1. Creates an RAII guard object.</span>
    <span class="doccomment">///    1. Wraps the guard in `Result` and returns it. If this instance has been poisoned,</span>
    <span class="doccomment">///       it is wrapped in an `Err`; otherwise wrapped in an `Ok`.</span>
    <span class="doccomment">/// 1. User accesses to the underlying data to read/write through the guard.</span>
    <span class="doccomment">///    (No other access is then.)</span>
    <span class="doccomment">/// 1. The guard is dropped (falls out of scope) and the lock is released.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`write`]: #method.write</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Errors</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// - If another user is holding any other lock (either read lock or write lock),</span>
    <span class="doccomment">///   [`TryLockError::WouldBlock`] is returned.</span>
    <span class="doccomment">/// - If this method call succeeded to acquire the lock, and if another user had panicked</span>
    <span class="doccomment">///   while holding the exclusive write lock, [`TryLockError::Poisoned`] is returned.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// [`TryLockError::WouldBlock`]: type.TryLockError.html</span>
    <span class="doccomment">/// [`TryLockError::Poisoned`]: type.TryLockError.html</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let lock = RwLock::new(1);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut guard = lock.try_write().unwrap();</span>
    <span class="doccomment">/// assert_eq!(1, *guard);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// *guard += 1;</span>
    <span class="doccomment">/// assert_eq!(2, *guard);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert!(lock.try_write().is_err());</span>
    <span class="doccomment">/// assert!(lock.try_read().is_err());</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">try_write</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">TryLockResult</span><span class="op">&lt;</span><span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span><span class="op">&gt;</span> {
        <span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_lock</span>(<span class="ident">acquire_exclusive_lock</span>, <span class="ident">is_locked</span>) {
            <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_locked</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="prelude-val">Err</span>(<span class="ident">TryLockError</span>::<span class="ident">WouldBlock</span>),
            <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_poisoned</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="prelude-val">Err</span>(<span class="ident">TryLockError</span>::<span class="ident">Poisoned</span>(<span class="ident">PoisonError</span>::<span class="ident">new</span>(
                <span class="ident">RwLockWriteGuard</span>::<span class="ident">new</span>(<span class="self">self</span>),
            ))),
            <span class="kw">_</span> <span class="op">=</span><span class="op">&gt;</span> <span class="prelude-val">Ok</span>(<span class="ident">RwLockWriteGuard</span>::<span class="ident">new</span>(<span class="self">self</span>)),
        }
    }

    <span class="doccomment">/// Blocks the current thread until acquiring the exclusive write lock, and</span>
    <span class="doccomment">/// returns an RAII guard object.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// The actual flow will be as follows.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// 1. User calls this method.</span>
    <span class="doccomment">///    1. Blocks until this thread acquires the exclusive write lock</span>
    <span class="doccomment">///       (i.e. until any other lock is held.)</span>
    <span class="doccomment">///    1. Creates an RAII guard object.</span>
    <span class="doccomment">///    1. Wrapps the guard in Result and returns it. If this instance has been</span>
    <span class="doccomment">///       poisoned, it is wrapped in an `Err`; otherwise wrapped in an `Ok`.</span>
    <span class="doccomment">/// 1. User accesses to the underlying data to read/write through the guard.</span>
    <span class="doccomment">///    (No other access is then.)</span>
    <span class="doccomment">/// 1. The guard is dropped (falls out of scope) and the lock is released.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Errors</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If another user panicked while holding the exclusive write lock of this instance,</span>
    <span class="doccomment">/// this method call wraps the guard in an error and returns it.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let lock = RwLock::new(0);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut guard = lock.write().unwrap();</span>
    <span class="doccomment">/// assert_eq!(0, *guard);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// *guard += 1;</span>
    <span class="doccomment">/// assert_eq!(1, *guard);</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(true, lock.try_read().is_err());</span>
    <span class="doccomment">/// assert_eq!(true, lock.try_write().is_err());</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">write</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockResult</span><span class="op">&lt;</span><span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span><span class="op">&gt;</span> {
        <span class="kw">loop</span> {
            <span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_lock</span>(<span class="ident">acquire_exclusive_lock</span>, <span class="ident">is_locked</span>) {
                <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_locked</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="ident">std</span>::<span class="ident">thread</span>::<span class="ident">yield_now</span>(),
                <span class="ident">s</span> <span class="kw">if</span> <span class="ident">is_poisoned</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">PoisonError</span>::<span class="ident">new</span>(<span class="ident">RwLockWriteGuard</span>::<span class="ident">new</span>(<span class="self">self</span>))),
                <span class="kw">_</span> <span class="op">=</span><span class="op">&gt;</span> <span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">RwLockWriteGuard</span>::<span class="ident">new</span>(<span class="self">self</span>)),
            }
        }
    }

    <span class="doccomment">/// Try to acquire lock and return the lock status before updated.</span>
    <span class="kw">fn</span> <span class="ident">try_lock</span><span class="op">&lt;</span><span class="ident">AcqFn</span>, <span class="ident">LockCheckFn</span><span class="op">&gt;</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">acq_fn</span>: <span class="ident">AcqFn</span>, <span class="ident">lock_check_fn</span>: <span class="ident">LockCheckFn</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockStatus</span>
    <span class="kw">where</span>
        <span class="ident">AcqFn</span>: <span class="ident">Fn</span>(<span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockStatus</span>,
        <span class="ident">LockCheckFn</span>: <span class="ident">Fn</span>(<span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">bool</span>,
    {
        <span class="comment">// Assume not poisoned, no user is holding the lock at first.</span>
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">expected</span> <span class="op">=</span> <span class="ident">INIT</span>;

        <span class="kw">loop</span> {
            <span class="comment">// Try to acquire the lock.</span>
            <span class="kw">let</span> <span class="ident">desired</span> <span class="op">=</span> <span class="ident">acq_fn</span>(<span class="ident">expected</span>);
            <span class="kw">let</span> <span class="ident">current</span> <span class="op">=</span> <span class="self">self</span>
                .<span class="ident">lock</span>
                .<span class="ident">compare_and_swap</span>(<span class="ident">expected</span>, <span class="ident">desired</span>, <span class="ident">Ordering</span>::<span class="ident">Acquire</span>);

            <span class="comment">// Succeeded.</span>
            <span class="kw">if</span> <span class="ident">current</span> <span class="op">=</span><span class="op">=</span> <span class="ident">expected</span> {
                <span class="kw">return</span> <span class="ident">current</span>;
            }

            <span class="comment">// Locked.</span>
            <span class="kw">if</span> <span class="ident">lock_check_fn</span>(<span class="ident">current</span>) {
                <span class="kw">return</span> <span class="ident">current</span>;
            }

            <span class="comment">// - The first assumption was wrong.</span>
            <span class="comment">// - Another user changes the lock status at the same time.</span>
            <span class="comment">// Try again soon.</span>
            <span class="ident">expected</span> <span class="op">=</span> <span class="ident">current</span>;
        }
    }

    <span class="doccomment">/// Determines whether the lock is poisoned or not.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Warning</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// This function won&#39;t acquire any lock. If another thread is active,</span>
    <span class="doccomment">/// the rwlock can become poisoned at any time. You should not trust a `false`</span>
    <span class="doccomment">/// value for program correctness without additional synchronization.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">/// use std::sync::Arc;</span>
    <span class="doccomment">/// use std::thread;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let lock = Arc::new(RwLock::new(0));</span>
    <span class="doccomment">/// assert_eq!(false, lock.is_poisoned());</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// {</span>
    <span class="doccomment">///     let lock = lock.clone();</span>
    <span class="doccomment">///</span>
    <span class="doccomment">///     let _ = thread::spawn(move || {</span>
    <span class="doccomment">///         // This panic while holding the lock (`_guard` is in scope) will poison</span>
    <span class="doccomment">///         // the instance.</span>
    <span class="doccomment">///         let _guard = lock.write().unwrap();</span>
    <span class="doccomment">///         panic!(&quot;Poison here&quot;);</span>
    <span class="doccomment">///     }).join();</span>
    <span class="doccomment">/// }</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// assert_eq!(true, lock.is_poisoned());</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is_poisoned</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">bool</span> {
        <span class="kw">let</span> <span class="ident">status</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);
        <span class="ident">is_poisoned</span>(<span class="ident">status</span>)
    }

    <span class="doccomment">/// Returns a mutable reference to the underlying data.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// Note that this method won&#39;t acquire any lock because we know there is</span>
    <span class="doccomment">/// no other references to `self`.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Errors</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If another user panicked while holding the exclusive write lock of this instance,</span>
    <span class="doccomment">/// this method call wraps the guard in an error and returns it.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// # Examples</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// ```</span>
    <span class="doccomment">/// use spin_sync::RwLock;</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// let mut lock = RwLock::new(0);</span>
    <span class="doccomment">/// *lock.get_mut().unwrap() = 10;</span>
    <span class="doccomment">/// assert_eq!(*lock.read().unwrap(), 10);</span>
    <span class="doccomment">/// ```</span>
    <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_mut</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockResult</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">T</span><span class="op">&gt;</span> {
        <span class="comment">// We know statically that there are no other references to `self`, so</span>
        <span class="comment">// there&#39;s no need to lock the inner lock.</span>
        <span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>() };
        <span class="kw">if</span> <span class="self">self</span>.<span class="ident">is_poisoned</span>() {
            <span class="prelude-val">Err</span>(<span class="ident">PoisonError</span>::<span class="ident">new</span>(<span class="ident">data</span>))
        } <span class="kw">else</span> {
            <span class="prelude-val">Ok</span>(<span class="ident">data</span>)
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> <span class="ident">From</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> <span class="kw">for</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="self">Self</span> {
        <span class="ident">RwLock</span>::<span class="ident">new</span>(<span class="ident">t</span>)
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="ident">Default</span><span class="op">&gt;</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">&gt;</span> <span class="self">Self</span> {
        <span class="ident">RwLock</span>::<span class="ident">new</span>(<span class="ident">T</span>::<span class="ident">default</span>())
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_read</span>() {
            <span class="prelude-val">Ok</span>(<span class="ident">guard</span>) <span class="op">=</span><span class="op">&gt;</span> <span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">&quot;RwLock&quot;</span>).<span class="ident">field</span>(<span class="string">&quot;data&quot;</span>, <span class="op">&amp;&amp;</span><span class="kw-2">*</span><span class="ident">guard</span>).<span class="ident">finish</span>(),
            <span class="prelude-val">Err</span>(<span class="ident">TryLockError</span>::<span class="ident">Poisoned</span>(<span class="ident">err</span>)) <span class="op">=</span><span class="op">&gt;</span> <span class="ident">f</span>
                .<span class="ident">debug_struct</span>(<span class="string">&quot;RwLock&quot;</span>)
                .<span class="ident">field</span>(<span class="string">&quot;data&quot;</span>, <span class="op">&amp;&amp;</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="ident">err</span>.<span class="ident">get_ref</span>())
                .<span class="ident">finish</span>(),
            <span class="prelude-val">Err</span>(<span class="ident">TryLockError</span>::<span class="ident">WouldBlock</span>) <span class="op">=</span><span class="op">&gt;</span> {
                <span class="kw">struct</span> <span class="ident">LockedPlaceholder</span>;
                <span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">LockedPlaceholder</span> {
                    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
                        <span class="ident">f</span>.<span class="ident">write_str</span>(<span class="string">&quot;&lt;locked&gt;&quot;</span>)
                    }
                }

                <span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">&quot;RwLock&quot;</span>)
                    .<span class="ident">field</span>(<span class="string">&quot;data&quot;</span>, <span class="kw-2">&amp;</span><span class="ident">LockedPlaceholder</span>)
                    .<span class="ident">finish</span>()
            }
        }
    }
}

<span class="doccomment">/// An RAII implementation of a &quot;scoped shared read lock&quot; of a RwLock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When this instance is dropped (falls out of scope), the lock will be released.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The data protected by the RwLock can be accessed to read</span>
<span class="doccomment">/// through this guard via its `Deref` implementation.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This instance is created by [`read`] and [`try_read`] methods on</span>
<span class="doccomment">/// [`RwLock`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`read`]: struct.RwLock.html#method.read</span>
<span class="doccomment">/// [`try_read`]: struct.RwLock.html#method.try_read</span>
<span class="doccomment">/// [`RwLock`]: struct.RwLock.html</span>
<span class="attribute">#[<span class="ident">must_use</span> <span class="op">=</span> <span class="string">&quot;if unused the RwLock will immediately unlock&quot;</span>]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">rwlock</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>,
    <span class="ident">_phantom</span>: <span class="ident">PhantomRwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span><span class="op">&gt;</span>, <span class="comment">// To implement !Send.</span>
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">rwlock</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="self">Self</span> {
        <span class="self">Self</span> {
            <span class="ident">rwlock</span>,
            <span class="ident">_phantom</span>: <span class="ident">Default</span>::<span class="ident">default</span>(),
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</span>;

    <span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="kw-2">&amp;</span><span class="self">Self</span>::<span class="ident">Target</span> {
        <span class="kw">unsafe</span> { <span class="kw-2">&amp;</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">rwlock</span>.<span class="ident">data</span>.<span class="ident">get</span>() }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Make sure to release the shared read lock.</span>
    <span class="doccomment">/// This function will never poison the rwlock.</span>
    <span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="comment">// Assume not poisoned and no other user is holding the lock at first.</span>
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">expected</span> <span class="op">=</span> <span class="ident">acquire_shared_lock</span>(<span class="ident">INIT</span>);

        <span class="kw">loop</span> {
            <span class="kw">let</span> <span class="ident">desired</span> <span class="op">=</span> <span class="ident">release_shared_lock</span>(<span class="ident">expected</span>);
            <span class="kw">let</span> <span class="ident">current</span> <span class="op">=</span> <span class="self">self</span>
                .<span class="ident">rwlock</span>
                .<span class="ident">lock</span>
                .<span class="ident">compare_and_swap</span>(<span class="ident">expected</span>, <span class="ident">desired</span>, <span class="ident">Ordering</span>::<span class="ident">Release</span>);

            <span class="comment">// Succeeded to release the lock.</span>
            <span class="kw">if</span> <span class="ident">current</span> <span class="op">=</span><span class="op">=</span> <span class="ident">expected</span> {
                <span class="kw">return</span>;
            }

            <span class="comment">// - Assumption was wrong.</span>
            <span class="comment">// - Another user release the lock at the same time.</span>
            <span class="comment">// Try again.</span>
            <span class="ident">expected</span> <span class="op">=</span> <span class="ident">current</span>;
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Display</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        (<span class="kw-2">*</span><span class="kw-2">*</span><span class="self">self</span>).<span class="ident">fmt</span>(<span class="ident">f</span>)
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">&quot;RwLockReadGuard&quot;</span>)
            .<span class="ident">field</span>(<span class="string">&quot;lock&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">rwlock</span>)
            .<span class="ident">finish</span>()
    }
}

<span class="doccomment">/// An RAII implementation of a &quot;scoped exclusive write lock&quot; of a RwLock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When this instance is dropped (falls out of scope), the lock will be released.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The data protected by the RwLock can be accessed to read/write</span>
<span class="doccomment">/// through this guard via its `Deref` and `DerefMut` implementation.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This instance is created by [`write`] and [`try_write`] methods on</span>
<span class="doccomment">/// [`RwLock`].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`write`]: struct.RwLock.html#method.write</span>
<span class="doccomment">/// [`try_write`]: struct.RwLock.html#method.try_write</span>
<span class="doccomment">/// [`RwLock`]: struct.RwLock.html</span>
<span class="attribute">#[<span class="ident">must_use</span> <span class="op">=</span> <span class="string">&quot;if unused the RwLock will immediately unlock&quot;</span>]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
    <span class="ident">rwlock</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>,
    <span class="ident">_phantom</span>: <span class="ident">PhantomRwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span><span class="op">&gt;</span>, <span class="comment">// To implement !Send.</span>
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">rwlock</span>: <span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="self">Self</span> {
        <span class="self">Self</span> {
            <span class="ident">rwlock</span>,
            <span class="ident">_phantom</span>: <span class="ident">Default</span>::<span class="ident">default</span>(),
        }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</span>;

    <span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&amp;</span><span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="kw-2">&amp;</span><span class="self">Self</span>::<span class="ident">Target</span> {
        <span class="kw">unsafe</span> { <span class="kw-2">&amp;</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">rwlock</span>.<span class="ident">data</span>.<span class="ident">get</span>() }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">Self</span>::<span class="ident">Target</span> {
        <span class="kw">unsafe</span> { <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">rwlock</span>.<span class="ident">data</span>.<span class="ident">get</span>() }
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="doccomment">/// Make sure to release the exclusive write lock.</span>
    <span class="doccomment">///</span>
    <span class="doccomment">/// If this user panicked, poison the lock.</span>
    <span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="self">self</span>) {
        <span class="kw">let</span> <span class="ident">old_status</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">rwlock</span>.<span class="ident">lock</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">Relaxed</span>);

        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">new_status</span> <span class="op">=</span> <span class="ident">release_exclusive_lock</span>(<span class="ident">old_status</span>);
        <span class="kw">if</span> <span class="ident">std</span>::<span class="ident">thread</span>::<span class="ident">panicking</span>() {
            <span class="ident">new_status</span> <span class="op">=</span> <span class="ident">set_poison_flag</span>(<span class="ident">new_status</span>);
        }

        <span class="self">self</span>.<span class="ident">rwlock</span>.<span class="ident">lock</span>.<span class="ident">store</span>(<span class="ident">new_status</span>, <span class="ident">Ordering</span>::<span class="ident">Release</span>);
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt</span>::<span class="ident">Display</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        (<span class="kw-2">*</span><span class="kw-2">*</span><span class="self">self</span>).<span class="ident">fmt</span>(<span class="ident">f</span>)
    }
}

<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {
    <span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&amp;</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span><span class="op">&gt;</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
        <span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">&quot;RwLockWriteGuard&quot;</span>)
            .<span class="ident">field</span>(<span class="string">&quot;lock&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.<span class="ident">rwlock</span>)
            .<span class="ident">finish</span>()
    }
}

<span class="comment">//</span>
<span class="comment">// Marker Traits</span>
<span class="comment">//</span>
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">UnwindSafe</span> <span class="kw">for</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {}
<span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">&gt;</span> <span class="ident">RefUnwindSafe</span> <span class="kw">for</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {}

<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Send</span><span class="op">&gt;</span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span><span class="op">&gt;</span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">RwLock</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span> {}

<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Sync</span><span class="op">&gt;</span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">RwLockReadGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op">&lt;</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">Sync</span><span class="op">&gt;</span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">RwLockWriteGuard</span><span class="op">&lt;</span><span class="lifetime">&#39;_</span>, <span class="ident">T</span><span class="op">&gt;</span> {}

<span class="comment">//</span>
<span class="comment">// Helpers for Lock State</span>
<span class="comment">//</span>
<span class="kw">type</span> <span class="ident">LockStatus</span> <span class="op">=</span> <span class="ident">u64</span>;

<span class="kw">const</span> <span class="ident">INIT</span>: <span class="ident">LockStatus</span> <span class="op">=</span> <span class="number">0</span>;
<span class="kw">const</span> <span class="ident">SHARED_LOCK_MASK</span>: <span class="ident">LockStatus</span> <span class="op">=</span> <span class="number">0x3fffffffffffffff</span>;
<span class="kw">const</span> <span class="ident">EXCLUSIVE_LOCK_FLAG</span>: <span class="ident">LockStatus</span> <span class="op">=</span> <span class="number">0x4000000000000000</span>;
<span class="kw">const</span> <span class="ident">POISON_FLAG</span>: <span class="ident">LockStatus</span> <span class="op">=</span> <span class="number">0x8000000000000000</span>;

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">is_poisoned</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">bool</span> {
    (<span class="ident">s</span> <span class="op">&amp;</span> <span class="ident">POISON_FLAG</span>) <span class="op">!</span><span class="op">=</span> <span class="number">0</span>
}

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">set_poison_flag</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockStatus</span> {
    <span class="ident">s</span> <span class="op">|</span> <span class="ident">POISON_FLAG</span>
}

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">is_locked</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">bool</span> {
    <span class="ident">s</span> <span class="op">&amp;</span> (<span class="op">!</span><span class="ident">POISON_FLAG</span>) <span class="op">!</span><span class="op">=</span> <span class="number">0</span>
}

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">is_locked_exclusively</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">bool</span> {
    <span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> (<span class="ident">s</span> <span class="op">&amp;</span> <span class="ident">EXCLUSIVE_LOCK_FLAG</span>) <span class="op">!</span><span class="op">=</span> <span class="number">0</span>;

    <span class="kw">if</span> <span class="ident">ret</span> {
        <span class="macro">debug_assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">s</span> <span class="op">&amp;</span> <span class="ident">SHARED_LOCK_MASK</span>);
    }

    <span class="ident">ret</span>
}

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">acquire_exclusive_lock</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockStatus</span> {
    <span class="macro">debug_assert_eq</span><span class="macro">!</span>(<span class="bool-val">false</span>, <span class="ident">is_locked</span>(<span class="ident">s</span>));
    <span class="ident">s</span> <span class="op">|</span> <span class="ident">EXCLUSIVE_LOCK_FLAG</span>
}

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">release_exclusive_lock</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockStatus</span> {
    <span class="macro">debug_assert_eq</span><span class="macro">!</span>(<span class="bool-val">true</span>, <span class="ident">is_locked_exclusively</span>(<span class="ident">s</span>));
    <span class="ident">s</span> <span class="op">&amp;</span> (<span class="op">!</span><span class="ident">EXCLUSIVE_LOCK_FLAG</span>)
}

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">count_shared_locks</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">u64</span> {
    <span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="ident">s</span> <span class="op">&amp;</span> <span class="ident">SHARED_LOCK_MASK</span>;

    <span class="kw">if</span> <span class="number">0</span> <span class="op">&lt;</span> <span class="ident">ret</span> {
        <span class="macro">debug_assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">s</span> <span class="op">&amp;</span> <span class="ident">EXCLUSIVE_LOCK_FLAG</span>);
    }

    <span class="ident">ret</span>
}

<span class="doccomment">/// # Panic</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Cause panic if the maximum count of shared locks are being holded. (maximum</span>
<span class="doccomment">/// number is 0x3fffffffffffffff.)</span>
<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">acquire_shared_lock</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockStatus</span> {
    <span class="macro">debug_assert_eq</span><span class="macro">!</span>(<span class="bool-val">false</span>, <span class="ident">is_locked_exclusively</span>(<span class="ident">s</span>));

    <span class="kw">if</span> <span class="ident">count_shared_locks</span>(<span class="ident">s</span>) <span class="op">=</span><span class="op">=</span> <span class="ident">SHARED_LOCK_MASK</span> {
        <span class="macro">panic</span><span class="macro">!</span>(<span class="string">&quot;rwlock maximum reader count exceeded&quot;</span>);
    }

    <span class="ident">s</span> <span class="op">+</span> <span class="number">1</span>
}

<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">release_shared_lock</span>(<span class="ident">s</span>: <span class="ident">LockStatus</span>) <span class="op">-</span><span class="op">&gt;</span> <span class="ident">LockStatus</span> {
    <span class="macro">debug_assert</span><span class="macro">!</span>(<span class="number">0</span> <span class="op">&lt;</span> <span class="ident">count_shared_locks</span>(<span class="ident">s</span>));
    <span class="ident">s</span> <span class="op">-</span> <span class="number">1</span>
}

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">rwlock_tests</span> {
    <span class="kw">use</span> <span class="kw">super</span>::<span class="kw-2">*</span>;

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">try_many_times</span>() {
        <span class="kw">let</span> <span class="ident">lock</span> <span class="op">=</span> <span class="ident">RwLock</span>::<span class="ident">new</span>(<span class="number">0</span>);

        <span class="comment">// Try to write at first.</span>
        {
            <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">guard0</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_write</span>().<span class="ident">unwrap</span>();
            <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="kw-2">*</span><span class="ident">guard0</span>);

            <span class="kw-2">*</span><span class="ident">guard0</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
            <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">1</span>, <span class="kw-2">*</span><span class="ident">guard0</span>);

            <span class="kw">let</span> <span class="ident">result1</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_read</span>();
            <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">result1</span>.<span class="ident">is_err</span>());

            <span class="kw">let</span> <span class="ident">result2</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_write</span>();
            <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">result2</span>.<span class="ident">is_err</span>());

            <span class="kw">let</span> <span class="ident">result3</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_read</span>();
            <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">result3</span>.<span class="ident">is_err</span>());

            <span class="kw">let</span> <span class="ident">result4</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_write</span>();
            <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">result4</span>.<span class="ident">is_err</span>());
        }

        <span class="comment">// Try to read at first.</span>
        {
            <span class="kw">let</span> <span class="ident">guard0</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_read</span>().<span class="ident">unwrap</span>();
            <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">1</span>, <span class="kw-2">*</span><span class="ident">guard0</span>);

            <span class="kw">let</span> <span class="ident">result1</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_write</span>();
            <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">result1</span>.<span class="ident">is_err</span>());

            <span class="kw">let</span> <span class="ident">guard2</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_read</span>().<span class="ident">unwrap</span>();
            <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">1</span>, <span class="kw-2">*</span><span class="ident">guard2</span>);

            <span class="kw">let</span> <span class="ident">result3</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_write</span>();
            <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">result3</span>.<span class="ident">is_err</span>());

            <span class="kw">let</span> <span class="ident">guard4</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_read</span>().<span class="ident">unwrap</span>();
            <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">1</span>, <span class="kw-2">*</span><span class="ident">guard4</span>);

            <span class="kw">let</span> <span class="ident">result5</span> <span class="op">=</span> <span class="ident">lock</span>.<span class="ident">try_write</span>();
            <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">result5</span>.<span class="ident">is_err</span>());
        }
    }
}

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">lock_state_tests</span> {
    <span class="kw">use</span> <span class="kw">super</span>::<span class="kw-2">*</span>;

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">flag_duplication</span>() {
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">INIT</span> <span class="op">&amp;</span> <span class="ident">SHARED_LOCK_MASK</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">INIT</span> <span class="op">&amp;</span> <span class="ident">EXCLUSIVE_LOCK_FLAG</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">INIT</span> <span class="op">&amp;</span> <span class="ident">POISON_FLAG</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">SHARED_LOCK_MASK</span> <span class="op">&amp;</span> <span class="ident">EXCLUSIVE_LOCK_FLAG</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">SHARED_LOCK_MASK</span> <span class="op">&amp;</span> <span class="ident">POISON_FLAG</span>);
        <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">0</span>, <span class="ident">EXCLUSIVE_LOCK_FLAG</span> <span class="op">&amp;</span> <span class="ident">POISON_FLAG</span>);
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">flag_uses_all_bits</span>() {
        <span class="macro">assert_eq</span><span class="macro">!</span>(
            <span class="ident">std</span>::<span class="ident">u64</span>::<span class="ident">MAX</span>,
            <span class="ident">INIT</span> <span class="op">|</span> <span class="ident">SHARED_LOCK_MASK</span> <span class="op">|</span> <span class="ident">EXCLUSIVE_LOCK_FLAG</span> <span class="op">|</span> <span class="ident">POISON_FLAG</span>
        );
    }
}
</pre></div>
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