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| </pre><pre class="rust"><code><span class="doccomment">//! Epoch-based memory reclamation. |
| //! |
| //! An interesting problem concurrent collections deal with comes from the remove operation. |
| //! Suppose that a thread removes an element from a lock-free map, while another thread is reading |
| //! that same element at the same time. The first thread must wait until the second thread stops |
| //! reading the element. Only then it is safe to destruct it. |
| //! |
| //! Programming languages that come with garbage collectors solve this problem trivially. The |
| //! garbage collector will destruct the removed element when no thread can hold a reference to it |
| //! anymore. |
| //! |
| //! This crate implements a basic memory reclamation mechanism, which is based on epochs. When an |
| //! element gets removed from a concurrent collection, it is inserted into a pile of garbage and |
| //! marked with the current epoch. Every time a thread accesses a collection, it checks the current |
| //! epoch, attempts to increment it, and destructs some garbage that became so old that no thread |
| //! can be referencing it anymore. |
| //! |
| //! That is the general mechanism behind epoch-based memory reclamation, but the details are a bit |
| //! more complicated. Anyhow, memory reclamation is designed to be fully automatic and something |
| //! users of concurrent collections don't have to worry much about. |
| //! |
| //! # Pointers |
| //! |
| //! Concurrent collections are built using atomic pointers. This module provides [`Atomic`], which |
| //! is just a shared atomic pointer to a heap-allocated object. Loading an [`Atomic`] yields a |
| //! [`Shared`], which is an epoch-protected pointer through which the loaded object can be safely |
| //! read. |
| //! |
| //! # Pinning |
| //! |
| //! Before an [`Atomic`] can be loaded, a participant must be [`pin`]ned. By pinning a participant |
| //! we declare that any object that gets removed from now on must not be destructed just |
| //! yet. Garbage collection of newly removed objects is suspended until the participant gets |
| //! unpinned. |
| //! |
| //! # Garbage |
| //! |
| //! Objects that get removed from concurrent collections must be stashed away until all currently |
| //! pinned participants get unpinned. Such objects can be stored into a thread-local or global |
| //! storage, where they are kept until the right time for their destruction comes. |
| //! |
| //! There is a global shared instance of garbage queue. You can [`defer`](Guard::defer) the execution of an |
| //! arbitrary function until the global epoch is advanced enough. Most notably, concurrent data |
| //! structures may defer the deallocation of an object. |
| //! |
| //! # APIs |
| //! |
| //! For majority of use cases, just use the default garbage collector by invoking [`pin`]. If you |
| //! want to create your own garbage collector, use the [`Collector`] API. |
| |
| </span><span class="attribute">#![doc(test( |
| no_crate_inject, |
| attr( |
| deny(warnings, rust_2018_idioms), |
| allow(dead_code, unused_assignments, unused_variables) |
| ) |
| ))] |
| #![warn( |
| missing_docs, |
| missing_debug_implementations, |
| rust_2018_idioms, |
| unreachable_pub |
| )] |
| #![cfg_attr(not(feature = <span class="string">"std"</span>), no_std)] |
| |
| #[cfg(crossbeam_loom)] |
| </span><span class="kw">extern crate </span>loom_crate <span class="kw">as </span>loom; |
| |
| <span class="kw">use </span>cfg_if::cfg_if; |
| |
| <span class="attribute">#[cfg(crossbeam_loom)] |
| #[allow(unused_imports, dead_code)] |
| </span><span class="kw">mod </span>primitive { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>cell { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>loom::cell::UnsafeCell; |
| } |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>sync { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>atomic { |
| <span class="kw">use </span>core::sync::atomic::Ordering; |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>loom::sync::atomic::{fence, AtomicUsize}; |
| |
| <span class="comment">// FIXME: loom does not support compiler_fence at the moment. |
| // https://github.com/tokio-rs/loom/issues/117 |
| // we use fence as a stand-in for compiler_fence for the time being. |
| // this may miss some races since fence is stronger than compiler_fence, |
| // but it's the best we can do for the time being. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span><span class="self">self</span>::fence <span class="kw">as </span>compiler_fence; |
| } |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>loom::sync::Arc; |
| } |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>loom::thread_local; |
| } |
| <span class="attribute">#[cfg(not(crossbeam_no_atomic_cas))] |
| #[cfg(not(crossbeam_loom))] |
| #[allow(unused_imports, dead_code)] |
| </span><span class="kw">mod </span>primitive { |
| <span class="attribute">#[cfg(feature = <span class="string">"alloc"</span>)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>cell { |
| <span class="attribute">#[derive(Debug)] |
| #[repr(transparent)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>UnsafeCell<T>(::core::cell::UnsafeCell<T>); |
| |
| <span class="comment">// loom's UnsafeCell has a slightly different API than the standard library UnsafeCell. |
| // Since we want the rest of the code to be agnostic to whether it's running under loom or |
| // not, we write this small wrapper that provides the loom-supported API for the standard |
| // library UnsafeCell. This is also what the loom documentation recommends: |
| // https://github.com/tokio-rs/loom#handling-loom-api-differences |
| </span><span class="kw">impl</span><T> UnsafeCell<T> { |
| <span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">const fn </span>new(data: T) -> UnsafeCell<T> { |
| UnsafeCell(::core::cell::UnsafeCell::new(data)) |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>with<R>(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw">impl </span>FnOnce(<span class="kw-2">*const </span>T) -> R) -> R { |
| f(<span class="self">self</span>.<span class="number">0</span>.get()) |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>with_mut<R>(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw">impl </span>FnOnce(<span class="kw-2">*mut </span>T) -> R) -> R { |
| f(<span class="self">self</span>.<span class="number">0</span>.get()) |
| } |
| } |
| } |
| <span class="attribute">#[cfg(feature = <span class="string">"alloc"</span>)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>sync { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">mod </span>atomic { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>core::sync::atomic::compiler_fence; |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>core::sync::atomic::fence; |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>core::sync::atomic::AtomicUsize; |
| } |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>alloc::sync::Arc; |
| } |
| |
| <span class="attribute">#[cfg(feature = <span class="string">"std"</span>)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">use </span>std::thread_local; |
| } |
| |
| <span class="attribute">#[cfg(not(crossbeam_no_atomic_cas))] |
| </span><span class="macro">cfg_if! </span>{ |
| <span class="kw">if </span><span class="attribute">#[cfg(feature = <span class="string">"alloc"</span>)] </span>{ |
| <span class="kw">extern crate </span>alloc; |
| |
| <span class="kw">mod </span>atomic; |
| <span class="kw">mod </span>collector; |
| <span class="kw">mod </span>deferred; |
| <span class="kw">mod </span>epoch; |
| <span class="kw">mod </span>guard; |
| <span class="kw">mod </span>internal; |
| <span class="kw">mod </span>sync; |
| |
| <span class="kw">pub use </span><span class="self">self</span>::atomic::{ |
| Pointable, Atomic, CompareExchangeError, |
| Owned, Pointer, Shared, |
| }; |
| <span class="kw">pub use </span><span class="self">self</span>::collector::{Collector, LocalHandle}; |
| <span class="kw">pub use </span><span class="self">self</span>::guard::{unprotected, Guard}; |
| |
| <span class="attribute">#[allow(deprecated)] |
| </span><span class="kw">pub use </span><span class="self">self</span>::atomic::{CompareAndSetError, CompareAndSetOrdering}; |
| } |
| } |
| |
| <span class="macro">cfg_if! </span>{ |
| <span class="kw">if </span><span class="attribute">#[cfg(feature = <span class="string">"std"</span>)] </span>{ |
| <span class="kw">mod </span>default; |
| <span class="kw">pub use </span><span class="self">self</span>::default::{default_collector, is_pinned, pin}; |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="crossbeam_epoch" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
