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Diffstat (limited to 'vendor/crossbeam-epoch/src/lib.rs')
| -rw-r--r-- | vendor/crossbeam-epoch/src/lib.rs | 167 |
1 files changed, 0 insertions, 167 deletions
diff --git a/vendor/crossbeam-epoch/src/lib.rs b/vendor/crossbeam-epoch/src/lib.rs deleted file mode 100644 index 96374ed..0000000 --- a/vendor/crossbeam-epoch/src/lib.rs +++ /dev/null @@ -1,167 +0,0 @@ -//! 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. - -#![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 = "std"), no_std)] - -#[cfg(crossbeam_loom)] -extern crate loom_crate as loom; - -use cfg_if::cfg_if; - -#[cfg(crossbeam_loom)] -#[allow(unused_imports, dead_code)] -mod primitive { - pub(crate) mod cell { - pub(crate) use loom::cell::UnsafeCell; - } - pub(crate) mod sync { - pub(crate) mod atomic { - pub(crate) use loom::sync::atomic::{fence, AtomicPtr, AtomicUsize, Ordering}; - - // 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. - pub(crate) use self::fence as compiler_fence; - } - pub(crate) use loom::sync::Arc; - } - pub(crate) use loom::thread_local; -} -#[cfg(target_has_atomic = "ptr")] -#[cfg(not(crossbeam_loom))] -#[allow(unused_imports, dead_code)] -mod primitive { - pub(crate) mod cell { - #[derive(Debug)] - #[repr(transparent)] - pub(crate) struct UnsafeCell<T>(::core::cell::UnsafeCell<T>); - - // 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 - impl<T> UnsafeCell<T> { - #[inline] - pub(crate) const fn new(data: T) -> UnsafeCell<T> { - UnsafeCell(::core::cell::UnsafeCell::new(data)) - } - - #[inline] - pub(crate) fn with<R>(&self, f: impl FnOnce(*const T) -> R) -> R { - f(self.0.get()) - } - - #[inline] - pub(crate) fn with_mut<R>(&self, f: impl FnOnce(*mut T) -> R) -> R { - f(self.0.get()) - } - } - } - pub(crate) mod sync { - pub(crate) mod atomic { - pub(crate) use core::sync::atomic::{ - compiler_fence, fence, AtomicPtr, AtomicUsize, Ordering, - }; - } - #[cfg(feature = "alloc")] - pub(crate) use alloc::sync::Arc; - } - - #[cfg(feature = "std")] - pub(crate) use std::thread_local; -} - -#[cfg(target_has_atomic = "ptr")] -cfg_if! { - if #[cfg(feature = "alloc")] { - extern crate alloc; - - mod atomic; - mod collector; - mod deferred; - mod epoch; - mod guard; - mod internal; - mod sync; - - pub use self::atomic::{ - Pointable, Atomic, CompareExchangeError, - Owned, Pointer, Shared, - }; - pub use self::collector::{Collector, LocalHandle}; - pub use self::guard::{unprotected, Guard}; - - #[allow(deprecated)] - pub use self::atomic::{CompareAndSetError, CompareAndSetOrdering}; - } -} - -cfg_if! { - if #[cfg(feature = "std")] { - mod default; - pub use self::default::{default_collector, is_pinned, pin}; - } -} |