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</pre><pre class="rust">
<span class="kw">use</span> <span class="ident">std::cell::UnsafeCell</span>;
<span class="kw">use</span> <span class="ident">std::collections::HashMap</span>;
<span class="kw">use</span> <span class="ident">std::fmt</span>;
<span class="kw">use</span> <span class="ident">std::marker::PhantomData</span>;
<span class="kw">use</span> <span class="ident">std::mem</span>;
<span class="kw">use</span> <span class="ident">std::ops</span>::{<span class="ident">Deref</span>, <span class="ident">DerefMut</span>};
<span class="kw">use</span> <span class="ident">std::panic</span>::{<span class="ident">RefUnwindSafe</span>, <span class="ident">UnwindSafe</span>};
<span class="kw">use</span> <span class="ident">std::sync</span>::{<span class="ident">LockResult</span>, <span class="ident">PoisonError</span>, <span class="ident">TryLockError</span>, <span class="ident">TryLockResult</span>};
<span class="kw">use</span> <span class="ident">std::sync</span>::{<span class="ident">Mutex</span>, <span class="ident">RwLock</span>, <span class="ident">RwLockReadGuard</span>, <span class="ident">RwLockWriteGuard</span>};
<span class="kw">use</span> <span class="ident">std::thread</span>::{<span class="self">self</span>, <span class="ident">ThreadId</span>};
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::CachePadded</span>;
<span class="kw">use</span> <span class="ident">lazy_static::lazy_static</span>;
<span class="doccomment">/// The number of shards per sharded lock. Must be a power of two.</span>
<span class="kw">const</span> <span class="ident">NUM_SHARDS</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">8</span>;
<span class="doccomment">/// A shard containing a single reader-writer lock.</span>
<span class="kw">struct</span> <span class="ident">Shard</span> {
<span class="doccomment">/// The inner reader-writer lock.</span>
<span class="ident">lock</span>: <span class="ident">RwLock</span><span class="op"><</span>()<span class="op">></span>,
<span class="doccomment">/// The write-guard keeping this shard locked.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Write operations will lock each shard and store the guard here. These guards get dropped at</span>
<span class="doccomment">/// the same time the big guard is dropped.</span>
<span class="ident">write_guard</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">RwLockWriteGuard</span><span class="op"><</span><span class="lifetime">'static</span>, ()<span class="op">></span><span class="op">></span><span class="op">></span>,
}
<span class="doccomment">/// A sharded reader-writer lock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This lock is equivalent to [`RwLock`], except read operations are faster and write operations</span>
<span class="doccomment">/// are slower.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A `ShardedLock` is internally made of a list of *shards*, each being a [`RwLock`] occupying a</span>
<span class="doccomment">/// single cache line. Read operations will pick one of the shards depending on the current thread</span>
<span class="doccomment">/// and lock it. Write operations need to lock all shards in succession.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// By splitting the lock into shards, concurrent read operations will in most cases choose</span>
<span class="doccomment">/// different shards and thus update different cache lines, which is good for scalability. However,</span>
<span class="doccomment">/// write operations need to do more work and are therefore slower than usual.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The priority policy of the lock is dependent on the underlying operating system's</span>
<span class="doccomment">/// implementation, and this type does not guarantee that any particular policy will be used.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Poisoning</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A `ShardedLock`, like [`RwLock`], will become poisoned on a panic. Note that it may only be</span>
<span class="doccomment">/// poisoned if a panic occurs while a write operation is in progress. If a panic occurs in any</span>
<span class="doccomment">/// read operation, the lock will not be poisoned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let lock = ShardedLock::new(5);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // Any number of read locks can be held at once.</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let r1 = lock.read().unwrap();</span>
<span class="doccomment">/// let r2 = lock.read().unwrap();</span>
<span class="doccomment">/// assert_eq!(*r1, 5);</span>
<span class="doccomment">/// assert_eq!(*r2, 5);</span>
<span class="doccomment">/// } // Read locks are dropped at this point.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// // However, only one write lock may be held.</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let mut w = lock.write().unwrap();</span>
<span class="doccomment">/// *w += 1;</span>
<span class="doccomment">/// assert_eq!(*w, 6);</span>
<span class="doccomment">/// } // Write lock is dropped here.</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`RwLock`]: std::sync::RwLock</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> {
<span class="doccomment">/// A list of locks protecting the internal data.</span>
<span class="ident">shards</span>: <span class="ident">Box</span><span class="op"><</span>[<span class="ident">CachePadded</span><span class="op"><</span><span class="ident">Shard</span><span class="op">></span>]<span class="op">></span>,
<span class="doccomment">/// The internal data.</span>
<span class="ident">value</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</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">Send</span> <span class="kw">for</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</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">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">UnwindSafe</span> <span class="kw">for</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">RefUnwindSafe</span> <span class="kw">for</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Creates a new sharded reader-writer lock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let lock = ShardedLock::new(5);</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">value</span>: <span class="ident">T</span>) <span class="op">-</span><span class="op">></span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">ShardedLock</span> {
<span class="ident">shards</span>: (<span class="number">0</span>..<span class="ident">NUM_SHARDS</span>)
.<span class="ident">map</span>(<span class="op">|</span><span class="kw">_</span><span class="op">|</span> {
<span class="ident">CachePadded::new</span>(<span class="ident">Shard</span> {
<span class="ident">lock</span>: <span class="ident">RwLock::new</span>(()),
<span class="ident">write_guard</span>: <span class="ident">UnsafeCell::new</span>(<span class="prelude-val">None</span>),
})
})
.<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Box</span><span class="op"><</span>[<span class="kw">_</span>]<span class="op">></span><span class="op">></span>(),
<span class="ident">value</span>: <span class="ident">UnsafeCell::new</span>(<span class="ident">value</span>),
}
}
<span class="doccomment">/// Consumes this lock, returning the underlying data.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method will return an error if the lock is poisoned. A lock gets poisoned when a write</span>
<span class="doccomment">/// operation panics.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let lock = ShardedLock::new(String::new());</span>
<span class="doccomment">/// {</span>
<span class="doccomment">/// let mut s = lock.write().unwrap();</span>
<span class="doccomment">/// *s = "modified".to_owned();</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// assert_eq!(lock.into_inner().unwrap(), "modified");</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">></span> <span class="ident">LockResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">is_poisoned</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">is_poisoned</span>();
<span class="kw">let</span> <span class="ident">inner</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">value</span>.<span class="ident">into_inner</span>();
<span class="kw">if</span> <span class="ident">is_poisoned</span> {
<span class="prelude-val">Err</span>(<span class="ident">PoisonError::new</span>(<span class="ident">inner</span>))
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="ident">inner</span>)
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Returns `true` if the lock is poisoned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If another thread can still access the lock, it may become poisoned at any time. A `false`</span>
<span class="doccomment">/// result should not be trusted 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 crossbeam_utils::sync::ShardedLock;</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(ShardedLock::new(0));</span>
<span class="doccomment">/// let c_lock = lock.clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let _ = thread::spawn(move || {</span>
<span class="doccomment">/// let _lock = c_lock.write().unwrap();</span>
<span class="doccomment">/// panic!(); // the lock gets poisoned</span>
<span class="doccomment">/// }).join();</span>
<span class="doccomment">/// assert_eq!(lock.is_poisoned(), true);</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">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="self">self</span>.<span class="ident">shards</span>[<span class="number">0</span>].<span class="ident">lock</span>.<span class="ident">is_poisoned</span>()
}
<span class="doccomment">/// Returns a mutable reference to the underlying data.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Since this call borrows the lock mutably, no actual locking needs to take place.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method will return an error if the lock is poisoned. A lock gets poisoned when a write</span>
<span class="doccomment">/// operation panics.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut lock = ShardedLock::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">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">LockResult</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">is_poisoned</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">is_poisoned</span>();
<span class="kw">let</span> <span class="ident">inner</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">value</span>.<span class="ident">get</span>() };
<span class="kw">if</span> <span class="ident">is_poisoned</span> {
<span class="prelude-val">Err</span>(<span class="ident">PoisonError::new</span>(<span class="ident">inner</span>))
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="ident">inner</span>)
}
}
<span class="doccomment">/// Attempts to acquire this lock with shared read access.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the access could not be granted at this time, an error is returned. Otherwise, a guard</span>
<span class="doccomment">/// is returned which will release the shared access when it is dropped. This method does not</span>
<span class="doccomment">/// provide any guarantees with respect to the ordering of whether contentious readers or</span>
<span class="doccomment">/// writers will acquire the lock first.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method will return an error if the lock is poisoned. A lock gets poisoned when a write</span>
<span class="doccomment">/// operation panics.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let lock = ShardedLock::new(1);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// match lock.try_read() {</span>
<span class="doccomment">/// Ok(n) => assert_eq!(*n, 1),</span>
<span class="doccomment">/// Err(_) => unreachable!(),</span>
<span class="doccomment">/// };</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">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">TryLockResult</span><span class="op"><</span><span class="ident">ShardedLockReadGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span><span class="op">></span> {
<span class="comment">// Take the current thread index and map it to a shard index. Thread indices will tend to</span>
<span class="comment">// distribute shards among threads equally, thus reducing contention due to read-locking.</span>
<span class="kw">let</span> <span class="ident">current_index</span> <span class="op">=</span> <span class="ident">current_index</span>().<span class="ident">unwrap_or</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">shard_index</span> <span class="op">=</span> <span class="ident">current_index</span> <span class="op">&</span> (<span class="self">self</span>.<span class="ident">shards</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>);
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">shards</span>[<span class="ident">shard_index</span>].<span class="ident">lock</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">></span> <span class="prelude-val">Ok</span>(<span class="ident">ShardedLockReadGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_guard</span>: <span class="ident">guard</span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
}),
<span class="prelude-val">Err</span>(<span class="ident">TryLockError::Poisoned</span>(<span class="ident">err</span>)) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">ShardedLockReadGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_guard</span>: <span class="ident">err</span>.<span class="ident">into_inner</span>(),
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
};
<span class="prelude-val">Err</span>(<span class="ident">TryLockError::Poisoned</span>(<span class="ident">PoisonError::new</span>(<span class="ident">guard</span>)))
}
<span class="prelude-val">Err</span>(<span class="ident">TryLockError::WouldBlock</span>) <span class="op">=</span><span class="op">></span> <span class="prelude-val">Err</span>(<span class="ident">TryLockError::WouldBlock</span>),
}
}
<span class="doccomment">/// Locks with shared read access, blocking the current thread until it can be acquired.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The calling thread will be blocked until there are no more writers which hold the lock.</span>
<span class="doccomment">/// There may be other readers currently inside the lock when this method returns. This method</span>
<span class="doccomment">/// does not provide any guarantees with respect to the ordering of whether contentious readers</span>
<span class="doccomment">/// or writers will acquire the lock first.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns a guard which will release the shared access when dropped.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method will return an error if the lock is poisoned. A lock gets poisoned when a write</span>
<span class="doccomment">/// operation panics.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method might panic when called if the lock is already held by the current thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</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(ShardedLock::new(1));</span>
<span class="doccomment">/// let c_lock = lock.clone();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let n = lock.read().unwrap();</span>
<span class="doccomment">/// assert_eq!(*n, 1);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// thread::spawn(move || {</span>
<span class="doccomment">/// let r = c_lock.read();</span>
<span class="doccomment">/// assert!(r.is_ok());</span>
<span class="doccomment">/// }).join().unwrap();</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">read</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">LockResult</span><span class="op"><</span><span class="ident">ShardedLockReadGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span><span class="op">></span> {
<span class="comment">// Take the current thread index and map it to a shard index. Thread indices will tend to</span>
<span class="comment">// distribute shards among threads equally, thus reducing contention due to read-locking.</span>
<span class="kw">let</span> <span class="ident">current_index</span> <span class="op">=</span> <span class="ident">current_index</span>().<span class="ident">unwrap_or</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">shard_index</span> <span class="op">=</span> <span class="ident">current_index</span> <span class="op">&</span> (<span class="self">self</span>.<span class="ident">shards</span>.<span class="ident">len</span>() <span class="op">-</span> <span class="number">1</span>);
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">shards</span>[<span class="ident">shard_index</span>].<span class="ident">lock</span>.<span class="ident">read</span>() {
<span class="prelude-val">Ok</span>(<span class="ident">guard</span>) <span class="op">=</span><span class="op">></span> <span class="prelude-val">Ok</span>(<span class="ident">ShardedLockReadGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_guard</span>: <span class="ident">guard</span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
}),
<span class="prelude-val">Err</span>(<span class="ident">err</span>) <span class="op">=</span><span class="op">></span> <span class="prelude-val">Err</span>(<span class="ident">PoisonError::new</span>(<span class="ident">ShardedLockReadGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_guard</span>: <span class="ident">err</span>.<span class="ident">into_inner</span>(),
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
})),
}
}
<span class="doccomment">/// Attempts to acquire this lock with exclusive write access.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the access could not be granted at this time, an error is returned. Otherwise, a guard</span>
<span class="doccomment">/// is returned which will release the exclusive access when it is dropped. This method does</span>
<span class="doccomment">/// not provide any guarantees with respect to the ordering of whether contentious readers or</span>
<span class="doccomment">/// writers will acquire the lock first.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method will return an error if the lock is poisoned. A lock gets poisoned when a write</span>
<span class="doccomment">/// operation panics.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let lock = ShardedLock::new(1);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let n = lock.read().unwrap();</span>
<span class="doccomment">/// assert_eq!(*n, 1);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// assert!(lock.try_write().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">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">TryLockResult</span><span class="op"><</span><span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span><span class="op">></span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">poisoned</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">blocked</span> <span class="op">=</span> <span class="prelude-val">None</span>;
<span class="comment">// Write-lock each shard in succession.</span>
<span class="kw">for</span> (<span class="ident">i</span>, <span class="ident">shard</span>) <span class="kw">in</span> <span class="self">self</span>.<span class="ident">shards</span>.<span class="ident">iter</span>().<span class="ident">enumerate</span>() {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">shard</span>.<span class="ident">lock</span>.<span class="ident">try_write</span>() {
<span class="prelude-val">Ok</span>(<span class="ident">guard</span>) <span class="op">=</span><span class="op">></span> <span class="ident">guard</span>,
<span class="prelude-val">Err</span>(<span class="ident">TryLockError::Poisoned</span>(<span class="ident">err</span>)) <span class="op">=</span><span class="op">></span> {
<span class="ident">poisoned</span> <span class="op">=</span> <span class="bool-val">true</span>;
<span class="ident">err</span>.<span class="ident">into_inner</span>()
}
<span class="prelude-val">Err</span>(<span class="ident">TryLockError::WouldBlock</span>) <span class="op">=</span><span class="op">></span> {
<span class="ident">blocked</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">i</span>);
<span class="kw">break</span>;
}
};
<span class="comment">// Store the guard into the shard.</span>
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">guard</span>: <span class="ident">RwLockWriteGuard</span><span class="op"><</span><span class="lifetime">'static</span>, ()<span class="op">></span> <span class="op">=</span> <span class="ident">mem::transmute</span>(<span class="ident">guard</span>);
<span class="kw">let</span> <span class="ident">dest</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">shard</span>.<span class="ident">write_guard</span>.<span class="ident">get</span>();
<span class="kw-2">*</span><span class="ident">dest</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">guard</span>);
}
}
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">i</span>) <span class="op">=</span> <span class="ident">blocked</span> {
<span class="comment">// Unlock the shards in reverse order of locking.</span>
<span class="kw">for</span> <span class="ident">shard</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">shards</span>[<span class="number">0</span>..<span class="ident">i</span>].<span class="ident">iter</span>().<span class="ident">rev</span>() {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">dest</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">shard</span>.<span class="ident">write_guard</span>.<span class="ident">get</span>();
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">mem::replace</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">dest</span>, <span class="prelude-val">None</span>);
<span class="ident">drop</span>(<span class="ident">guard</span>);
}
}
<span class="prelude-val">Err</span>(<span class="ident">TryLockError::WouldBlock</span>)
} <span class="kw">else</span> <span class="kw">if</span> <span class="ident">poisoned</span> {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">ShardedLockWriteGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
};
<span class="prelude-val">Err</span>(<span class="ident">TryLockError::Poisoned</span>(<span class="ident">PoisonError::new</span>(<span class="ident">guard</span>)))
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="ident">ShardedLockWriteGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
})
}
}
<span class="doccomment">/// Locks with exclusive write access, blocking the current thread until it can be acquired.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The calling thread will be blocked until there are no more writers which hold the lock.</span>
<span class="doccomment">/// There may be other readers currently inside the lock when this method returns. This method</span>
<span class="doccomment">/// does not provide any guarantees with respect to the ordering of whether contentious readers</span>
<span class="doccomment">/// or writers will acquire the lock first.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns a guard which will release the exclusive access when dropped.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method will return an error if the lock is poisoned. A lock gets poisoned when a write</span>
<span class="doccomment">/// operation panics.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method might panic when called if the lock is already held by the current thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use crossbeam_utils::sync::ShardedLock;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let lock = ShardedLock::new(1);</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut n = lock.write().unwrap();</span>
<span class="doccomment">/// *n = 2;</span>
<span class="doccomment">///</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">write</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">LockResult</span><span class="op"><</span><span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span><span class="op">></span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">poisoned</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="comment">// Write-lock each shard in succession.</span>
<span class="kw">for</span> <span class="ident">shard</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">shards</span>.<span class="ident">iter</span>() {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">shard</span>.<span class="ident">lock</span>.<span class="ident">write</span>() {
<span class="prelude-val">Ok</span>(<span class="ident">guard</span>) <span class="op">=</span><span class="op">></span> <span class="ident">guard</span>,
<span class="prelude-val">Err</span>(<span class="ident">err</span>) <span class="op">=</span><span class="op">></span> {
<span class="ident">poisoned</span> <span class="op">=</span> <span class="bool-val">true</span>;
<span class="ident">err</span>.<span class="ident">into_inner</span>()
}
};
<span class="comment">// Store the guard into the shard.</span>
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">guard</span>: <span class="ident">RwLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, ()<span class="op">></span> <span class="op">=</span> <span class="ident">guard</span>;
<span class="kw">let</span> <span class="ident">guard</span>: <span class="ident">RwLockWriteGuard</span><span class="op"><</span><span class="lifetime">'static</span>, ()<span class="op">></span> <span class="op">=</span> <span class="ident">mem::transmute</span>(<span class="ident">guard</span>);
<span class="kw">let</span> <span class="ident">dest</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">shard</span>.<span class="ident">write_guard</span>.<span class="ident">get</span>();
<span class="kw-2">*</span><span class="ident">dest</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">guard</span>);
}
}
<span class="kw">if</span> <span class="ident">poisoned</span> {
<span class="prelude-val">Err</span>(<span class="ident">PoisonError::new</span>(<span class="ident">ShardedLockWriteGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
}))
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="ident">ShardedLockWriteGuard</span> {
<span class="ident">lock</span>: <span class="self">self</span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span>,
})
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt::Debug</span><span class="op">></span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::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">></span> <span class="ident">f</span>
.<span class="ident">debug_struct</span>(<span class="string">"ShardedLock"</span>)
.<span class="ident">field</span>(<span class="string">"data"</span>, <span class="op">&&</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::Poisoned</span>(<span class="ident">err</span>)) <span class="op">=</span><span class="op">></span> <span class="ident">f</span>
.<span class="ident">debug_struct</span>(<span class="string">"ShardedLock"</span>)
.<span class="ident">field</span>(<span class="string">"data"</span>, <span class="op">&&</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::WouldBlock</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">struct</span> <span class="ident">LockedPlaceholder</span>;
<span class="kw">impl</span> <span class="ident">fmt::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">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">write_str</span>(<span class="string">"<locked>"</span>)
}
}
<span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"ShardedLock"</span>)
.<span class="ident">field</span>(<span class="string">"data"</span>, <span class="kw-2">&</span><span class="ident">LockedPlaceholder</span>)
.<span class="ident">finish</span>()
}
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Default</span><span class="op">></span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">></span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">ShardedLock::new</span>(<span class="ident">Default::default</span>())
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></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">></span> <span class="self">Self</span> {
<span class="ident">ShardedLock::new</span>(<span class="ident">t</span>)
}
}
<span class="doccomment">/// A guard used to release the shared read access of a [`ShardedLock`] when dropped.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ShardedLockReadGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> {
<span class="ident">lock</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">_guard</span>: <span class="ident">RwLockReadGuard</span><span class="op"><</span><span class="lifetime">'a</span>, ()<span class="op">></span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span><span class="op"><</span><span class="ident">RwLockReadGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span><span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</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">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">ShardedLockReadGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">ShardedLockReadGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></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">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">value</span>.<span class="ident">get</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">fmt::Debug</span><span class="op">></span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">ShardedLockReadGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"ShardedLockReadGuard"</span>)
.<span class="ident">field</span>(<span class="string">"lock"</span>, <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">lock</span>)
.<span class="ident">finish</span>()
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt::Display</span><span class="op">></span> <span class="ident">fmt::Display</span> <span class="kw">for</span> <span class="ident">ShardedLockReadGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::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="doccomment">/// A guard used to release the exclusive write access of a [`ShardedLock`] when dropped.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> {
<span class="ident">lock</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">ShardedLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">_marker</span>: <span class="ident">PhantomData</span><span class="op"><</span><span class="ident">RwLockWriteGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span><span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</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">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="comment">// Unlock the shards in reverse order of locking.</span>
<span class="kw">for</span> <span class="ident">shard</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">shards</span>.<span class="ident">iter</span>().<span class="ident">rev</span>() {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">dest</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">shard</span>.<span class="ident">write_guard</span>.<span class="ident">get</span>();
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">mem::replace</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">dest</span>, <span class="prelude-val">None</span>);
<span class="ident">drop</span>(<span class="ident">guard</span>);
}
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">fmt::Debug</span><span class="op">></span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"ShardedLockWriteGuard"</span>)
.<span class="ident">field</span>(<span class="string">"lock"</span>, <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">lock</span>)
.<span class="ident">finish</span>()
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span> <span class="op">+</span> <span class="ident">fmt::Display</span><span class="op">></span> <span class="ident">fmt::Display</span> <span class="kw">for</span> <span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::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"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></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">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">value</span>.<span class="ident">get</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">ShardedLockWriteGuard</span><span class="op"><</span><span class="lifetime">'_</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">lock</span>.<span class="ident">value</span>.<span class="ident">get</span>() }
}
}
<span class="doccomment">/// Returns a `usize` that identifies the current thread.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Each thread is associated with an 'index'. While there are no particular guarantees, indices</span>
<span class="doccomment">/// usually tend to be consecutive numbers between 0 and the number of running threads.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Since this function accesses TLS, `None` might be returned if the current thread's TLS is</span>
<span class="doccomment">/// tearing down.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">current_index</span>() <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span> {
<span class="ident">REGISTRATION</span>.<span class="ident">try_with</span>(<span class="op">|</span><span class="ident">reg</span><span class="op">|</span> <span class="ident">reg</span>.<span class="ident">index</span>).<span class="ident">ok</span>()
}
<span class="doccomment">/// The global registry keeping track of registered threads and indices.</span>
<span class="kw">struct</span> <span class="ident">ThreadIndices</span> {
<span class="doccomment">/// Mapping from `ThreadId` to thread index.</span>
<span class="ident">mapping</span>: <span class="ident">HashMap</span><span class="op"><</span><span class="ident">ThreadId</span>, <span class="ident">usize</span><span class="op">></span>,
<span class="doccomment">/// A list of free indices.</span>
<span class="ident">free_list</span>: <span class="ident">Vec</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>,
<span class="doccomment">/// The next index to allocate if the free list is empty.</span>
<span class="ident">next_index</span>: <span class="ident">usize</span>,
}
<span class="macro">lazy_static!</span> {
<span class="kw">static</span> <span class="kw-2">ref</span> <span class="ident">THREAD_INDICES</span>: <span class="ident">Mutex</span><span class="op"><</span><span class="ident">ThreadIndices</span><span class="op">></span> <span class="op">=</span> <span class="ident">Mutex::new</span>(<span class="ident">ThreadIndices</span> {
<span class="ident">mapping</span>: <span class="ident">HashMap::new</span>(),
<span class="ident">free_list</span>: <span class="ident">Vec::new</span>(),
<span class="ident">next_index</span>: <span class="number">0</span>,
});
}
<span class="doccomment">/// A registration of a thread with an index.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When dropped, unregisters the thread and frees the reserved index.</span>
<span class="kw">struct</span> <span class="ident">Registration</span> {
<span class="ident">index</span>: <span class="ident">usize</span>,
<span class="ident">thread_id</span>: <span class="ident">ThreadId</span>,
}
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Registration</span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">indices</span> <span class="op">=</span> <span class="ident">THREAD_INDICES</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="ident">indices</span>.<span class="ident">mapping</span>.<span class="ident">remove</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">thread_id</span>);
<span class="ident">indices</span>.<span class="ident">free_list</span>.<span class="ident">push</span>(<span class="self">self</span>.<span class="ident">index</span>);
}
}
<span class="macro">thread_local!</span> {
<span class="kw">static</span> <span class="ident">REGISTRATION</span>: <span class="ident">Registration</span> <span class="op">=</span> {
<span class="kw">let</span> <span class="ident">thread_id</span> <span class="op">=</span> <span class="ident">thread::current</span>().<span class="ident">id</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">indices</span> <span class="op">=</span> <span class="ident">THREAD_INDICES</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw">let</span> <span class="ident">index</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">indices</span>.<span class="ident">free_list</span>.<span class="ident">pop</span>() {
<span class="prelude-val">Some</span>(<span class="ident">i</span>) <span class="op">=</span><span class="op">></span> <span class="ident">i</span>,
<span class="prelude-val">None</span> <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">i</span> <span class="op">=</span> <span class="ident">indices</span>.<span class="ident">next_index</span>;
<span class="ident">indices</span>.<span class="ident">next_index</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
<span class="ident">i</span>
}
};
<span class="ident">indices</span>.<span class="ident">mapping</span>.<span class="ident">insert</span>(<span class="ident">thread_id</span>, <span class="ident">index</span>);
<span class="ident">Registration</span> {
<span class="ident">index</span>,
<span class="ident">thread_id</span>,
}
};
}
</pre></div>
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