| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/crossbeam-utils-0.8.15/src/sync/sharded_lock.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>sharded_lock.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../source-script.js"></script><script defer src="../../../source-files.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../crossbeam_utils/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../crossbeam_utils/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| <span id="636">636</span> |
| </pre><pre class="rust"><code><span class="kw">use </span>std::cell::UnsafeCell; |
| <span class="kw">use </span>std::collections::HashMap; |
| <span class="kw">use </span>std::fmt; |
| <span class="kw">use </span>std::marker::PhantomData; |
| <span class="kw">use </span>std::mem; |
| <span class="kw">use </span>std::ops::{Deref, DerefMut}; |
| <span class="kw">use </span>std::panic::{RefUnwindSafe, UnwindSafe}; |
| <span class="kw">use </span>std::sync::{LockResult, PoisonError, TryLockError, TryLockResult}; |
| <span class="kw">use </span>std::sync::{Mutex, RwLock, RwLockReadGuard, RwLockWriteGuard}; |
| <span class="kw">use </span>std::thread::{<span class="self">self</span>, ThreadId}; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::sync::once_lock::OnceLock; |
| <span class="kw">use </span><span class="kw">crate</span>::CachePadded; |
| |
| <span class="doccomment">/// The number of shards per sharded lock. Must be a power of two. |
| </span><span class="kw">const </span>NUM_SHARDS: usize = <span class="number">8</span>; |
| |
| <span class="doccomment">/// A shard containing a single reader-writer lock. |
| </span><span class="kw">struct </span>Shard { |
| <span class="doccomment">/// The inner reader-writer lock. |
| </span>lock: RwLock<()>, |
| |
| <span class="doccomment">/// The write-guard keeping this shard locked. |
| /// |
| /// Write operations will lock each shard and store the guard here. These guards get dropped at |
| /// the same time the big guard is dropped. |
| </span>write_guard: UnsafeCell<<span class="prelude-ty">Option</span><RwLockWriteGuard<<span class="lifetime">'static</span>, ()>>>, |
| } |
| |
| <span class="doccomment">/// A sharded reader-writer lock. |
| /// |
| /// This lock is equivalent to [`RwLock`], except read operations are faster and write operations |
| /// are slower. |
| /// |
| /// A `ShardedLock` is internally made of a list of *shards*, each being a [`RwLock`] occupying a |
| /// single cache line. Read operations will pick one of the shards depending on the current thread |
| /// and lock it. Write operations need to lock all shards in succession. |
| /// |
| /// By splitting the lock into shards, concurrent read operations will in most cases choose |
| /// different shards and thus update different cache lines, which is good for scalability. However, |
| /// write operations need to do more work and are therefore slower than usual. |
| /// |
| /// The priority policy of the lock is dependent on the underlying operating system's |
| /// implementation, and this type does not guarantee that any particular policy will be used. |
| /// |
| /// # Poisoning |
| /// |
| /// A `ShardedLock`, like [`RwLock`], will become poisoned on a panic. Note that it may only be |
| /// poisoned if a panic occurs while a write operation is in progress. If a panic occurs in any |
| /// read operation, the lock will not be poisoned. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// |
| /// let lock = ShardedLock::new(5); |
| /// |
| /// // Any number of read locks can be held at once. |
| /// { |
| /// let r1 = lock.read().unwrap(); |
| /// let r2 = lock.read().unwrap(); |
| /// assert_eq!(*r1, 5); |
| /// assert_eq!(*r2, 5); |
| /// } // Read locks are dropped at this point. |
| /// |
| /// // However, only one write lock may be held. |
| /// { |
| /// let mut w = lock.write().unwrap(); |
| /// *w += 1; |
| /// assert_eq!(*w, 6); |
| /// } // Write lock is dropped here. |
| /// ``` |
| /// |
| /// [`RwLock`]: std::sync::RwLock |
| </span><span class="kw">pub struct </span>ShardedLock<T: <span class="question-mark">?</span>Sized> { |
| <span class="doccomment">/// A list of locks protecting the internal data. |
| </span>shards: Box<[CachePadded<Shard>]>, |
| |
| <span class="doccomment">/// The internal data. |
| </span>value: UnsafeCell<T>, |
| } |
| |
| <span class="kw">unsafe impl</span><T: <span class="question-mark">?</span>Sized + Send> Send <span class="kw">for </span>ShardedLock<T> {} |
| <span class="kw">unsafe impl</span><T: <span class="question-mark">?</span>Sized + Send + Sync> Sync <span class="kw">for </span>ShardedLock<T> {} |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> UnwindSafe <span class="kw">for </span>ShardedLock<T> {} |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> RefUnwindSafe <span class="kw">for </span>ShardedLock<T> {} |
| |
| <span class="kw">impl</span><T> ShardedLock<T> { |
| <span class="doccomment">/// Creates a new sharded reader-writer lock. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// |
| /// let lock = ShardedLock::new(5); |
| /// ``` |
| </span><span class="kw">pub fn </span>new(value: T) -> ShardedLock<T> { |
| ShardedLock { |
| shards: (<span class="number">0</span>..NUM_SHARDS) |
| .map(|<span class="kw">_</span>| { |
| CachePadded::new(Shard { |
| lock: RwLock::new(()), |
| write_guard: UnsafeCell::new(<span class="prelude-val">None</span>), |
| }) |
| }) |
| .collect::<Box<[<span class="kw">_</span>]>>(), |
| value: UnsafeCell::new(value), |
| } |
| } |
| |
| <span class="doccomment">/// Consumes this lock, returning the underlying data. |
| /// |
| /// # Errors |
| /// |
| /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write |
| /// operation panics. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// |
| /// let lock = ShardedLock::new(String::new()); |
| /// { |
| /// let mut s = lock.write().unwrap(); |
| /// *s = "modified".to_owned(); |
| /// } |
| /// assert_eq!(lock.into_inner().unwrap(), "modified"); |
| /// ``` |
| </span><span class="kw">pub fn </span>into_inner(<span class="self">self</span>) -> LockResult<T> { |
| <span class="kw">let </span>is_poisoned = <span class="self">self</span>.is_poisoned(); |
| <span class="kw">let </span>inner = <span class="self">self</span>.value.into_inner(); |
| |
| <span class="kw">if </span>is_poisoned { |
| <span class="prelude-val">Err</span>(PoisonError::new(inner)) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Ok</span>(inner) |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> ShardedLock<T> { |
| <span class="doccomment">/// Returns `true` if the lock is poisoned. |
| /// |
| /// If another thread can still access the lock, it may become poisoned at any time. A `false` |
| /// result should not be trusted without additional synchronization. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// use std::sync::Arc; |
| /// use std::thread; |
| /// |
| /// let lock = Arc::new(ShardedLock::new(0)); |
| /// let c_lock = lock.clone(); |
| /// |
| /// let _ = thread::spawn(move || { |
| /// let _lock = c_lock.write().unwrap(); |
| /// panic!(); // the lock gets poisoned |
| /// }).join(); |
| /// assert_eq!(lock.is_poisoned(), true); |
| /// ``` |
| </span><span class="kw">pub fn </span>is_poisoned(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.shards[<span class="number">0</span>].lock.is_poisoned() |
| } |
| |
| <span class="doccomment">/// Returns a mutable reference to the underlying data. |
| /// |
| /// Since this call borrows the lock mutably, no actual locking needs to take place. |
| /// |
| /// # Errors |
| /// |
| /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write |
| /// operation panics. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// |
| /// let mut lock = ShardedLock::new(0); |
| /// *lock.get_mut().unwrap() = 10; |
| /// assert_eq!(*lock.read().unwrap(), 10); |
| /// ``` |
| </span><span class="kw">pub fn </span>get_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> LockResult<<span class="kw-2">&mut </span>T> { |
| <span class="kw">let </span>is_poisoned = <span class="self">self</span>.is_poisoned(); |
| <span class="kw">let </span>inner = <span class="kw">unsafe </span>{ <span class="kw-2">&mut *</span><span class="self">self</span>.value.get() }; |
| |
| <span class="kw">if </span>is_poisoned { |
| <span class="prelude-val">Err</span>(PoisonError::new(inner)) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Ok</span>(inner) |
| } |
| } |
| |
| <span class="doccomment">/// Attempts to acquire this lock with shared read access. |
| /// |
| /// If the access could not be granted at this time, an error is returned. Otherwise, a guard |
| /// is returned which will release the shared access when it is dropped. This method does not |
| /// provide any guarantees with respect to the ordering of whether contentious readers or |
| /// writers will acquire the lock first. |
| /// |
| /// # Errors |
| /// |
| /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write |
| /// operation panics. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// |
| /// let lock = ShardedLock::new(1); |
| /// |
| /// match lock.try_read() { |
| /// Ok(n) => assert_eq!(*n, 1), |
| /// Err(_) => unreachable!(), |
| /// }; |
| /// ``` |
| </span><span class="kw">pub fn </span>try_read(<span class="kw-2">&</span><span class="self">self</span>) -> TryLockResult<ShardedLockReadGuard<<span class="lifetime">'_</span>, T>> { |
| <span class="comment">// Take the current thread index and map it to a shard index. Thread indices will tend to |
| // distribute shards among threads equally, thus reducing contention due to read-locking. |
| </span><span class="kw">let </span>current_index = current_index().unwrap_or(<span class="number">0</span>); |
| <span class="kw">let </span>shard_index = current_index & (<span class="self">self</span>.shards.len() - <span class="number">1</span>); |
| |
| <span class="kw">match </span><span class="self">self</span>.shards[shard_index].lock.try_read() { |
| <span class="prelude-val">Ok</span>(guard) => <span class="prelude-val">Ok</span>(ShardedLockReadGuard { |
| lock: <span class="self">self</span>, |
| _guard: guard, |
| _marker: PhantomData, |
| }), |
| <span class="prelude-val">Err</span>(TryLockError::Poisoned(err)) => { |
| <span class="kw">let </span>guard = ShardedLockReadGuard { |
| lock: <span class="self">self</span>, |
| _guard: err.into_inner(), |
| _marker: PhantomData, |
| }; |
| <span class="prelude-val">Err</span>(TryLockError::Poisoned(PoisonError::new(guard))) |
| } |
| <span class="prelude-val">Err</span>(TryLockError::WouldBlock) => <span class="prelude-val">Err</span>(TryLockError::WouldBlock), |
| } |
| } |
| |
| <span class="doccomment">/// Locks with shared read access, blocking the current thread until it can be acquired. |
| /// |
| /// The calling thread will be blocked until there are no more writers which hold the lock. |
| /// There may be other readers currently inside the lock when this method returns. This method |
| /// does not provide any guarantees with respect to the ordering of whether contentious readers |
| /// or writers will acquire the lock first. |
| /// |
| /// Returns a guard which will release the shared access when dropped. |
| /// |
| /// # Errors |
| /// |
| /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write |
| /// operation panics. |
| /// |
| /// # Panics |
| /// |
| /// This method might panic when called if the lock is already held by the current thread. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// use std::sync::Arc; |
| /// use std::thread; |
| /// |
| /// let lock = Arc::new(ShardedLock::new(1)); |
| /// let c_lock = lock.clone(); |
| /// |
| /// let n = lock.read().unwrap(); |
| /// assert_eq!(*n, 1); |
| /// |
| /// thread::spawn(move || { |
| /// let r = c_lock.read(); |
| /// assert!(r.is_ok()); |
| /// }).join().unwrap(); |
| /// ``` |
| </span><span class="kw">pub fn </span>read(<span class="kw-2">&</span><span class="self">self</span>) -> LockResult<ShardedLockReadGuard<<span class="lifetime">'_</span>, T>> { |
| <span class="comment">// Take the current thread index and map it to a shard index. Thread indices will tend to |
| // distribute shards among threads equally, thus reducing contention due to read-locking. |
| </span><span class="kw">let </span>current_index = current_index().unwrap_or(<span class="number">0</span>); |
| <span class="kw">let </span>shard_index = current_index & (<span class="self">self</span>.shards.len() - <span class="number">1</span>); |
| |
| <span class="kw">match </span><span class="self">self</span>.shards[shard_index].lock.read() { |
| <span class="prelude-val">Ok</span>(guard) => <span class="prelude-val">Ok</span>(ShardedLockReadGuard { |
| lock: <span class="self">self</span>, |
| _guard: guard, |
| _marker: PhantomData, |
| }), |
| <span class="prelude-val">Err</span>(err) => <span class="prelude-val">Err</span>(PoisonError::new(ShardedLockReadGuard { |
| lock: <span class="self">self</span>, |
| _guard: err.into_inner(), |
| _marker: PhantomData, |
| })), |
| } |
| } |
| |
| <span class="doccomment">/// Attempts to acquire this lock with exclusive write access. |
| /// |
| /// If the access could not be granted at this time, an error is returned. Otherwise, a guard |
| /// is returned which will release the exclusive access when it is dropped. This method does |
| /// not provide any guarantees with respect to the ordering of whether contentious readers or |
| /// writers will acquire the lock first. |
| /// |
| /// # Errors |
| /// |
| /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write |
| /// operation panics. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// |
| /// let lock = ShardedLock::new(1); |
| /// |
| /// let n = lock.read().unwrap(); |
| /// assert_eq!(*n, 1); |
| /// |
| /// assert!(lock.try_write().is_err()); |
| /// ``` |
| </span><span class="kw">pub fn </span>try_write(<span class="kw-2">&</span><span class="self">self</span>) -> TryLockResult<ShardedLockWriteGuard<<span class="lifetime">'_</span>, T>> { |
| <span class="kw">let </span><span class="kw-2">mut </span>poisoned = <span class="bool-val">false</span>; |
| <span class="kw">let </span><span class="kw-2">mut </span>blocked = <span class="prelude-val">None</span>; |
| |
| <span class="comment">// Write-lock each shard in succession. |
| </span><span class="kw">for </span>(i, shard) <span class="kw">in </span><span class="self">self</span>.shards.iter().enumerate() { |
| <span class="kw">let </span>guard = <span class="kw">match </span>shard.lock.try_write() { |
| <span class="prelude-val">Ok</span>(guard) => guard, |
| <span class="prelude-val">Err</span>(TryLockError::Poisoned(err)) => { |
| poisoned = <span class="bool-val">true</span>; |
| err.into_inner() |
| } |
| <span class="prelude-val">Err</span>(TryLockError::WouldBlock) => { |
| blocked = <span class="prelude-val">Some</span>(i); |
| <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>guard: RwLockWriteGuard<<span class="lifetime">'static</span>, ()> = mem::transmute(guard); |
| <span class="kw">let </span>dest: <span class="kw-2">*mut </span><span class="kw">_ </span>= shard.write_guard.get(); |
| <span class="kw-2">*</span>dest = <span class="prelude-val">Some</span>(guard); |
| } |
| } |
| |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(i) = blocked { |
| <span class="comment">// Unlock the shards in reverse order of locking. |
| </span><span class="kw">for </span>shard <span class="kw">in </span><span class="self">self</span>.shards[<span class="number">0</span>..i].iter().rev() { |
| <span class="kw">unsafe </span>{ |
| <span class="kw">let </span>dest: <span class="kw-2">*mut </span><span class="kw">_ </span>= shard.write_guard.get(); |
| <span class="kw">let </span>guard = mem::replace(<span class="kw-2">&mut *</span>dest, <span class="prelude-val">None</span>); |
| drop(guard); |
| } |
| } |
| <span class="prelude-val">Err</span>(TryLockError::WouldBlock) |
| } <span class="kw">else if </span>poisoned { |
| <span class="kw">let </span>guard = ShardedLockWriteGuard { |
| lock: <span class="self">self</span>, |
| _marker: PhantomData, |
| }; |
| <span class="prelude-val">Err</span>(TryLockError::Poisoned(PoisonError::new(guard))) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Ok</span>(ShardedLockWriteGuard { |
| lock: <span class="self">self</span>, |
| _marker: PhantomData, |
| }) |
| } |
| } |
| |
| <span class="doccomment">/// Locks with exclusive write access, blocking the current thread until it can be acquired. |
| /// |
| /// The calling thread will be blocked until there are no more writers which hold the lock. |
| /// There may be other readers currently inside the lock when this method returns. This method |
| /// does not provide any guarantees with respect to the ordering of whether contentious readers |
| /// or writers will acquire the lock first. |
| /// |
| /// Returns a guard which will release the exclusive access when dropped. |
| /// |
| /// # Errors |
| /// |
| /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write |
| /// operation panics. |
| /// |
| /// # Panics |
| /// |
| /// This method might panic when called if the lock is already held by the current thread. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use crossbeam_utils::sync::ShardedLock; |
| /// |
| /// let lock = ShardedLock::new(1); |
| /// |
| /// let mut n = lock.write().unwrap(); |
| /// *n = 2; |
| /// |
| /// assert!(lock.try_read().is_err()); |
| /// ``` |
| </span><span class="kw">pub fn </span>write(<span class="kw-2">&</span><span class="self">self</span>) -> LockResult<ShardedLockWriteGuard<<span class="lifetime">'_</span>, T>> { |
| <span class="kw">let </span><span class="kw-2">mut </span>poisoned = <span class="bool-val">false</span>; |
| |
| <span class="comment">// Write-lock each shard in succession. |
| </span><span class="kw">for </span>shard <span class="kw">in </span><span class="self">self</span>.shards.iter() { |
| <span class="kw">let </span>guard = <span class="kw">match </span>shard.lock.write() { |
| <span class="prelude-val">Ok</span>(guard) => guard, |
| <span class="prelude-val">Err</span>(err) => { |
| poisoned = <span class="bool-val">true</span>; |
| err.into_inner() |
| } |
| }; |
| |
| <span class="comment">// Store the guard into the shard. |
| </span><span class="kw">unsafe </span>{ |
| <span class="kw">let </span>guard: RwLockWriteGuard<<span class="lifetime">'_</span>, ()> = guard; |
| <span class="kw">let </span>guard: RwLockWriteGuard<<span class="lifetime">'static</span>, ()> = mem::transmute(guard); |
| <span class="kw">let </span>dest: <span class="kw-2">*mut </span><span class="kw">_ </span>= shard.write_guard.get(); |
| <span class="kw-2">*</span>dest = <span class="prelude-val">Some</span>(guard); |
| } |
| } |
| |
| <span class="kw">if </span>poisoned { |
| <span class="prelude-val">Err</span>(PoisonError::new(ShardedLockWriteGuard { |
| lock: <span class="self">self</span>, |
| _marker: PhantomData, |
| })) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Ok</span>(ShardedLockWriteGuard { |
| lock: <span class="self">self</span>, |
| _marker: PhantomData, |
| }) |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized + fmt::Debug> fmt::Debug <span class="kw">for </span>ShardedLock<T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| <span class="kw">match </span><span class="self">self</span>.try_read() { |
| <span class="prelude-val">Ok</span>(guard) => f |
| .debug_struct(<span class="string">"ShardedLock"</span>) |
| .field(<span class="string">"data"</span>, &&<span class="kw-2">*</span>guard) |
| .finish(), |
| <span class="prelude-val">Err</span>(TryLockError::Poisoned(err)) => f |
| .debug_struct(<span class="string">"ShardedLock"</span>) |
| .field(<span class="string">"data"</span>, &&<span class="kw-2">**</span>err.get_ref()) |
| .finish(), |
| <span class="prelude-val">Err</span>(TryLockError::WouldBlock) => { |
| <span class="kw">struct </span>LockedPlaceholder; |
| <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>LockedPlaceholder { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| f.write_str(<span class="string">"<locked>"</span>) |
| } |
| } |
| f.debug_struct(<span class="string">"ShardedLock"</span>) |
| .field(<span class="string">"data"</span>, <span class="kw-2">&</span>LockedPlaceholder) |
| .finish() |
| } |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T: Default> Default <span class="kw">for </span>ShardedLock<T> { |
| <span class="kw">fn </span>default() -> ShardedLock<T> { |
| ShardedLock::new(Default::default()) |
| } |
| } |
| |
| <span class="kw">impl</span><T> From<T> <span class="kw">for </span>ShardedLock<T> { |
| <span class="kw">fn </span>from(t: T) -> <span class="self">Self </span>{ |
| ShardedLock::new(t) |
| } |
| } |
| |
| <span class="doccomment">/// A guard used to release the shared read access of a [`ShardedLock`] when dropped. |
| </span><span class="attribute">#[clippy::has_significant_drop] |
| </span><span class="kw">pub struct </span>ShardedLockReadGuard<<span class="lifetime">'a</span>, T: <span class="question-mark">?</span>Sized> { |
| lock: <span class="kw-2">&</span><span class="lifetime">'a </span>ShardedLock<T>, |
| _guard: RwLockReadGuard<<span class="lifetime">'a</span>, ()>, |
| _marker: PhantomData<RwLockReadGuard<<span class="lifetime">'a</span>, T>>, |
| } |
| |
| <span class="kw">unsafe impl</span><T: <span class="question-mark">?</span>Sized + Sync> Sync <span class="kw">for </span>ShardedLockReadGuard<<span class="lifetime">'_</span>, T> {} |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> Deref <span class="kw">for </span>ShardedLockReadGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">type </span>Target = T; |
| |
| <span class="kw">fn </span>deref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="kw">unsafe </span>{ <span class="kw-2">&*</span><span class="self">self</span>.lock.value.get() } |
| } |
| } |
| |
| <span class="kw">impl</span><T: fmt::Debug> fmt::Debug <span class="kw">for </span>ShardedLockReadGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| f.debug_struct(<span class="string">"ShardedLockReadGuard"</span>) |
| .field(<span class="string">"lock"</span>, <span class="kw-2">&</span><span class="self">self</span>.lock) |
| .finish() |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized + fmt::Display> fmt::Display <span class="kw">for </span>ShardedLockReadGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| (<span class="kw-2">**</span><span class="self">self</span>).fmt(f) |
| } |
| } |
| |
| <span class="doccomment">/// A guard used to release the exclusive write access of a [`ShardedLock`] when dropped. |
| </span><span class="attribute">#[clippy::has_significant_drop] |
| </span><span class="kw">pub struct </span>ShardedLockWriteGuard<<span class="lifetime">'a</span>, T: <span class="question-mark">?</span>Sized> { |
| lock: <span class="kw-2">&</span><span class="lifetime">'a </span>ShardedLock<T>, |
| _marker: PhantomData<RwLockWriteGuard<<span class="lifetime">'a</span>, T>>, |
| } |
| |
| <span class="kw">unsafe impl</span><T: <span class="question-mark">?</span>Sized + Sync> Sync <span class="kw">for </span>ShardedLockWriteGuard<<span class="lifetime">'_</span>, T> {} |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> Drop <span class="kw">for </span>ShardedLockWriteGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>drop(<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>shard <span class="kw">in </span><span class="self">self</span>.lock.shards.iter().rev() { |
| <span class="kw">unsafe </span>{ |
| <span class="kw">let </span>dest: <span class="kw-2">*mut </span><span class="kw">_ </span>= shard.write_guard.get(); |
| <span class="kw">let </span>guard = mem::replace(<span class="kw-2">&mut *</span>dest, <span class="prelude-val">None</span>); |
| drop(guard); |
| } |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T: fmt::Debug> fmt::Debug <span class="kw">for </span>ShardedLockWriteGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| f.debug_struct(<span class="string">"ShardedLockWriteGuard"</span>) |
| .field(<span class="string">"lock"</span>, <span class="kw-2">&</span><span class="self">self</span>.lock) |
| .finish() |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized + fmt::Display> fmt::Display <span class="kw">for </span>ShardedLockWriteGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| (<span class="kw-2">**</span><span class="self">self</span>).fmt(f) |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> Deref <span class="kw">for </span>ShardedLockWriteGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">type </span>Target = T; |
| |
| <span class="kw">fn </span>deref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="kw">unsafe </span>{ <span class="kw-2">&*</span><span class="self">self</span>.lock.value.get() } |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> DerefMut <span class="kw">for </span>ShardedLockWriteGuard<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>deref_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>T { |
| <span class="kw">unsafe </span>{ <span class="kw-2">&mut *</span><span class="self">self</span>.lock.value.get() } |
| } |
| } |
| |
| <span class="doccomment">/// Returns a `usize` that identifies the current thread. |
| /// |
| /// Each thread is associated with an 'index'. While there are no particular guarantees, indices |
| /// usually tend to be consecutive numbers between 0 and the number of running threads. |
| /// |
| /// Since this function accesses TLS, `None` might be returned if the current thread's TLS is |
| /// tearing down. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">fn </span>current_index() -> <span class="prelude-ty">Option</span><usize> { |
| REGISTRATION.try_with(|reg| reg.index).ok() |
| } |
| |
| <span class="doccomment">/// The global registry keeping track of registered threads and indices. |
| </span><span class="kw">struct </span>ThreadIndices { |
| <span class="doccomment">/// Mapping from `ThreadId` to thread index. |
| </span>mapping: HashMap<ThreadId, usize>, |
| |
| <span class="doccomment">/// A list of free indices. |
| </span>free_list: Vec<usize>, |
| |
| <span class="doccomment">/// The next index to allocate if the free list is empty. |
| </span>next_index: usize, |
| } |
| |
| <span class="kw">fn </span>thread_indices() -> <span class="kw-2">&</span><span class="lifetime">'static </span>Mutex<ThreadIndices> { |
| <span class="kw">static </span>THREAD_INDICES: OnceLock<Mutex<ThreadIndices>> = OnceLock::new(); |
| <span class="kw">fn </span>init() -> Mutex<ThreadIndices> { |
| Mutex::new(ThreadIndices { |
| mapping: HashMap::new(), |
| free_list: Vec::new(), |
| next_index: <span class="number">0</span>, |
| }) |
| } |
| THREAD_INDICES.get_or_init(init) |
| } |
| |
| <span class="doccomment">/// A registration of a thread with an index. |
| /// |
| /// When dropped, unregisters the thread and frees the reserved index. |
| </span><span class="kw">struct </span>Registration { |
| index: usize, |
| thread_id: ThreadId, |
| } |
| |
| <span class="kw">impl </span>Drop <span class="kw">for </span>Registration { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">let </span><span class="kw-2">mut </span>indices = thread_indices().lock().unwrap(); |
| indices.mapping.remove(<span class="kw-2">&</span><span class="self">self</span>.thread_id); |
| indices.free_list.push(<span class="self">self</span>.index); |
| } |
| } |
| |
| <span class="macro">thread_local! </span>{ |
| <span class="kw">static </span>REGISTRATION: Registration = { |
| <span class="kw">let </span>thread_id = thread::current().id(); |
| <span class="kw">let </span><span class="kw-2">mut </span>indices = thread_indices().lock().unwrap(); |
| |
| <span class="kw">let </span>index = <span class="kw">match </span>indices.free_list.pop() { |
| <span class="prelude-val">Some</span>(i) => i, |
| <span class="prelude-val">None </span>=> { |
| <span class="kw">let </span>i = indices.next_index; |
| indices.next_index += <span class="number">1</span>; |
| i |
| } |
| }; |
| indices.mapping.insert(thread_id, index); |
| |
| Registration { |
| index, |
| thread_id, |
| } |
| }; |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="crossbeam_utils" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |