| <!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/arc-swap-1.6.0/src/docs/limitations.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>limitations.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="../../../arc_swap/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="../../../arc_swap/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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| </pre><pre class="rust"><code><span class="doccomment">//! Limitations and common pitfalls. |
| //! |
| //! # Sized types |
| //! |
| //! This currently works only for `Sized` types. Unsized types have „fat pointers“, which are twice |
| //! as large as the normal ones. The [`AtomicPtr`] doesn't support them. One could use something |
| //! like `AtomicU128` for them. The catch is this doesn't exist and the difference would make it |
| //! really hard to implement the debt storage/stripped down hazard pointers. |
| //! |
| //! A workaround is to use double indirection: |
| //! |
| //! ```rust |
| //! # use arc_swap::ArcSwap; |
| //! // This doesn't work: |
| //! // let data: ArcSwap<[u8]> = ArcSwap::new(Arc::from([1, 2, 3])); |
| //! |
| //! // But this does: |
| //! let data: ArcSwap<Box<[u8]>> = ArcSwap::from_pointee(Box::new([1, 2, 3])); |
| //! # drop(data); |
| //! ``` |
| //! |
| //! It also may be possible to use `ArcSwap` with the [`triomphe::ThinArc`] (that crate needs |
| //! enabling a feature flag to cooperate with `ArcSwap`). |
| //! |
| //! # Too many [`Guard`]s |
| //! |
| //! There's only limited number of "fast" slots for borrowing from [`ArcSwap`] for each single |
| //! thread (currently 8, but this might change in future versions). If these run out, the algorithm |
| //! falls back to slower path. |
| //! |
| //! If too many [`Guard`]s are kept around, the performance might be poor. These are not intended |
| //! to be stored in data structures or used across async yield points. |
| //! |
| //! [`ArcSwap`]: crate::ArcSwap |
| //! [`Guard`]: crate::Guard |
| //! [`AtomicPtr`]: std::sync::atomic::AtomicPtr |
| //! |
| //! # No `Clone` implementation |
| //! |
| //! Previous version implemented [`Clone`], but it turned out to be very confusing to people, since |
| //! it created fully independent [`ArcSwap`]. Users expected the instances to be tied to each |
| //! other, that store in one would change the result of future load of the other. |
| //! |
| //! To emulate the original behaviour, one can do something like this: |
| //! |
| //! ```rust |
| //! # use arc_swap::ArcSwap; |
| //! # let old = ArcSwap::from_pointee(42); |
| //! let new = ArcSwap::new(old.load_full()); |
| //! # let _ = new; |
| //! ``` |
| //! |
| //! [`triomphe::ThinArc`]: https://docs.rs/triomphe/latest/triomphe/struct.ThinArc.html |
| </span></code></pre></div> |
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