| <!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/git/checkouts/tokio-377c595163f99a10/dfe252d/tokio/src/runtime/time/entry.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>entry.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="../../../../tokio/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="../../../../tokio/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">//! Timer state structures. |
| //! |
| //! This module contains the heart of the intrusive timer implementation, and as |
| //! such the structures inside are full of tricky concurrency and unsafe code. |
| //! |
| //! # Ground rules |
| //! |
| //! The heart of the timer implementation here is the [`TimerShared`] structure, |
| //! shared between the [`TimerEntry`] and the driver. Generally, we permit access |
| //! to [`TimerShared`] ONLY via either 1) a mutable reference to [`TimerEntry`] or |
| //! 2) a held driver lock. |
| //! |
| //! It follows from this that any changes made while holding BOTH 1 and 2 will |
| //! be reliably visible, regardless of ordering. This is because of the acq/rel |
| //! fences on the driver lock ensuring ordering with 2, and rust mutable |
| //! reference rules for 1 (a mutable reference to an object can't be passed |
| //! between threads without an acq/rel barrier, and same-thread we have local |
| //! happens-before ordering). |
| //! |
| //! # State field |
| //! |
| //! Each timer has a state field associated with it. This field contains either |
| //! the current scheduled time, or a special flag value indicating its state. |
| //! This state can either indicate that the timer is on the 'pending' queue (and |
| //! thus will be fired with an `Ok(())` result soon) or that it has already been |
| //! fired/deregistered. |
| //! |
| //! This single state field allows for code that is firing the timer to |
| //! synchronize with any racing `reset` calls reliably. |
| //! |
| //! # Cached vs true timeouts |
| //! |
| //! To allow for the use case of a timeout that is periodically reset before |
| //! expiration to be as lightweight as possible, we support optimistically |
| //! lock-free timer resets, in the case where a timer is rescheduled to a later |
| //! point than it was originally scheduled for. |
| //! |
| //! This is accomplished by lazily rescheduling timers. That is, we update the |
| //! state field with the true expiration of the timer from the holder of |
| //! the [`TimerEntry`]. When the driver services timers (ie, whenever it's |
| //! walking lists of timers), it checks this "true when" value, and reschedules |
| //! based on it. |
| //! |
| //! We do, however, also need to track what the expiration time was when we |
| //! originally registered the timer; this is used to locate the right linked |
| //! list when the timer is being cancelled. This is referred to as the "cached |
| //! when" internally. |
| //! |
| //! There is of course a race condition between timer reset and timer |
| //! expiration. If the driver fails to observe the updated expiration time, it |
| //! could trigger expiration of the timer too early. However, because |
| //! [`mark_pending`][mark_pending] performs a compare-and-swap, it will identify this race and |
| //! refuse to mark the timer as pending. |
| //! |
| //! [mark_pending]: TimerHandle::mark_pending |
| |
| </span><span class="kw">use </span><span class="kw">crate</span>::loom::cell::UnsafeCell; |
| <span class="kw">use </span><span class="kw">crate</span>::loom::sync::atomic::AtomicU64; |
| <span class="kw">use </span><span class="kw">crate</span>::loom::sync::atomic::Ordering; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::runtime::scheduler; |
| <span class="kw">use </span><span class="kw">crate</span>::sync::AtomicWaker; |
| <span class="kw">use </span><span class="kw">crate</span>::time::Instant; |
| <span class="kw">use </span><span class="kw">crate</span>::util::linked_list; |
| |
| <span class="kw">use </span>std::cell::UnsafeCell <span class="kw">as </span>StdUnsafeCell; |
| <span class="kw">use </span>std::task::{Context, Poll, Waker}; |
| <span class="kw">use </span>std::{marker::PhantomPinned, pin::Pin, ptr::NonNull}; |
| |
| <span class="kw">type </span>TimerResult = <span class="prelude-ty">Result</span><(), <span class="kw">crate</span>::time::error::Error>; |
| |
| <span class="kw">const </span>STATE_DEREGISTERED: u64 = u64::MAX; |
| <span class="kw">const </span>STATE_PENDING_FIRE: u64 = STATE_DEREGISTERED - <span class="number">1</span>; |
| <span class="kw">const </span>STATE_MIN_VALUE: u64 = STATE_PENDING_FIRE; |
| |
| <span class="doccomment">/// This structure holds the current shared state of the timer - its scheduled |
| /// time (if registered), or otherwise the result of the timer completing, as |
| /// well as the registered waker. |
| /// |
| /// Generally, the StateCell is only permitted to be accessed from two contexts: |
| /// Either a thread holding the corresponding &mut TimerEntry, or a thread |
| /// holding the timer driver lock. The write actions on the StateCell amount to |
| /// passing "ownership" of the StateCell between these contexts; moving a timer |
| /// from the TimerEntry to the driver requires _both_ holding the &mut |
| /// TimerEntry and the driver lock, while moving it back (firing the timer) |
| /// requires only the driver lock. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>StateCell { |
| <span class="doccomment">/// Holds either the scheduled expiration time for this timer, or (if the |
| /// timer has been fired and is unregistered), `u64::MAX`. |
| </span>state: AtomicU64, |
| <span class="doccomment">/// If the timer is fired (an Acquire order read on state shows |
| /// `u64::MAX`), holds the result that should be returned from |
| /// polling the timer. Otherwise, the contents are unspecified and reading |
| /// without holding the driver lock is undefined behavior. |
| </span>result: UnsafeCell<TimerResult>, |
| <span class="doccomment">/// The currently-registered waker |
| </span>waker: CachePadded<AtomicWaker>, |
| } |
| |
| <span class="kw">impl </span>Default <span class="kw">for </span>StateCell { |
| <span class="kw">fn </span>default() -> <span class="self">Self </span>{ |
| <span class="self">Self</span>::new() |
| } |
| } |
| |
| <span class="kw">impl </span>std::fmt::Debug <span class="kw">for </span>StateCell { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>std::fmt::Formatter<<span class="lifetime">'_</span>>) -> std::fmt::Result { |
| <span class="macro">write!</span>(f, <span class="string">"StateCell({:?})"</span>, <span class="self">self</span>.read_state()) |
| } |
| } |
| |
| <span class="kw">impl </span>StateCell { |
| <span class="kw">fn </span>new() -> <span class="self">Self </span>{ |
| <span class="self">Self </span>{ |
| state: AtomicU64::new(STATE_DEREGISTERED), |
| result: UnsafeCell::new(<span class="prelude-val">Ok</span>(())), |
| waker: CachePadded(AtomicWaker::new()), |
| } |
| } |
| |
| <span class="kw">fn </span>is_pending(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.state.load(Ordering::Relaxed) == STATE_PENDING_FIRE |
| } |
| |
| <span class="doccomment">/// Returns the current expiration time, or None if not currently scheduled. |
| </span><span class="kw">fn </span>when(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><u64> { |
| <span class="kw">let </span>cur_state = <span class="self">self</span>.state.load(Ordering::Relaxed); |
| |
| <span class="kw">if </span>cur_state == u64::MAX { |
| <span class="prelude-val">None |
| </span>} <span class="kw">else </span>{ |
| <span class="prelude-val">Some</span>(cur_state) |
| } |
| } |
| |
| <span class="doccomment">/// If the timer is completed, returns the result of the timer. Otherwise, |
| /// returns None and registers the waker. |
| </span><span class="kw">fn </span>poll(<span class="kw-2">&</span><span class="self">self</span>, waker: <span class="kw-2">&</span>Waker) -> Poll<TimerResult> { |
| <span class="comment">// We must register first. This ensures that either `fire` will |
| // observe the new waker, or we will observe a racing fire to have set |
| // the state, or both. |
| </span><span class="self">self</span>.waker.<span class="number">0</span>.register_by_ref(waker); |
| |
| <span class="self">self</span>.read_state() |
| } |
| |
| <span class="kw">fn </span>read_state(<span class="kw-2">&</span><span class="self">self</span>) -> Poll<TimerResult> { |
| <span class="kw">let </span>cur_state = <span class="self">self</span>.state.load(Ordering::Acquire); |
| |
| <span class="kw">if </span>cur_state == STATE_DEREGISTERED { |
| <span class="comment">// SAFETY: The driver has fired this timer; this involves writing |
| // the result, and then writing (with release ordering) the state |
| // field. |
| </span>Poll::Ready(<span class="kw">unsafe </span>{ <span class="self">self</span>.result.with(|p| <span class="kw-2">*</span>p) }) |
| } <span class="kw">else </span>{ |
| Poll::Pending |
| } |
| } |
| |
| <span class="doccomment">/// Marks this timer as being moved to the pending list, if its scheduled |
| /// time is not after `not_after`. |
| /// |
| /// If the timer is scheduled for a time after not_after, returns an Err |
| /// containing the current scheduled time. |
| /// |
| /// SAFETY: Must hold the driver lock. |
| </span><span class="kw">unsafe fn </span>mark_pending(<span class="kw-2">&</span><span class="self">self</span>, not_after: u64) -> <span class="prelude-ty">Result</span><(), u64> { |
| <span class="comment">// Quick initial debug check to see if the timer is already fired. Since |
| // firing the timer can only happen with the driver lock held, we know |
| // we shouldn't be able to "miss" a transition to a fired state, even |
| // with relaxed ordering. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>cur_state = <span class="self">self</span>.state.load(Ordering::Relaxed); |
| |
| <span class="kw">loop </span>{ |
| <span class="comment">// improve the error message for things like |
| // https://github.com/tokio-rs/tokio/issues/3675 |
| </span><span class="macro">assert!</span>( |
| cur_state < STATE_MIN_VALUE, |
| <span class="string">"mark_pending called when the timer entry is in an invalid state" |
| </span>); |
| |
| <span class="kw">if </span>cur_state > not_after { |
| <span class="kw">break </span><span class="prelude-val">Err</span>(cur_state); |
| } |
| |
| <span class="kw">match </span><span class="self">self</span>.state.compare_exchange( |
| cur_state, |
| STATE_PENDING_FIRE, |
| Ordering::AcqRel, |
| Ordering::Acquire, |
| ) { |
| <span class="prelude-val">Ok</span>(<span class="kw">_</span>) => { |
| <span class="kw">break </span><span class="prelude-val">Ok</span>(()); |
| } |
| <span class="prelude-val">Err</span>(actual_state) => { |
| cur_state = actual_state; |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Fires the timer, setting the result to the provided result. |
| /// |
| /// Returns: |
| /// * `Some(waker) - if fired and a waker needs to be invoked once the |
| /// driver lock is released |
| /// * `None` - if fired and a waker does not need to be invoked, or if |
| /// already fired |
| /// |
| /// SAFETY: The driver lock must be held. |
| </span><span class="kw">unsafe fn </span>fire(<span class="kw-2">&</span><span class="self">self</span>, result: TimerResult) -> <span class="prelude-ty">Option</span><Waker> { |
| <span class="comment">// Quick initial check to see if the timer is already fired. Since |
| // firing the timer can only happen with the driver lock held, we know |
| // we shouldn't be able to "miss" a transition to a fired state, even |
| // with relaxed ordering. |
| </span><span class="kw">let </span>cur_state = <span class="self">self</span>.state.load(Ordering::Relaxed); |
| <span class="kw">if </span>cur_state == STATE_DEREGISTERED { |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| |
| <span class="comment">// SAFETY: We assume the driver lock is held and the timer is not |
| // fired, so only the driver is accessing this field. |
| // |
| // We perform a release-ordered store to state below, to ensure this |
| // write is visible before the state update is visible. |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.result.with_mut(|p| <span class="kw-2">*</span>p = result) }; |
| |
| <span class="self">self</span>.state.store(STATE_DEREGISTERED, Ordering::Release); |
| |
| <span class="self">self</span>.waker.<span class="number">0</span>.take_waker() |
| } |
| |
| <span class="doccomment">/// Marks the timer as registered (poll will return None) and sets the |
| /// expiration time. |
| /// |
| /// While this function is memory-safe, it should only be called from a |
| /// context holding both `&mut TimerEntry` and the driver lock. |
| </span><span class="kw">fn </span>set_expiration(<span class="kw-2">&</span><span class="self">self</span>, timestamp: u64) { |
| <span class="macro">debug_assert!</span>(timestamp < STATE_MIN_VALUE); |
| |
| <span class="comment">// We can use relaxed ordering because we hold the driver lock and will |
| // fence when we release the lock. |
| </span><span class="self">self</span>.state.store(timestamp, Ordering::Relaxed); |
| } |
| |
| <span class="doccomment">/// Attempts to adjust the timer to a new timestamp. |
| /// |
| /// If the timer has already been fired, is pending firing, or the new |
| /// timestamp is earlier than the old timestamp, (or occasionally |
| /// spuriously) returns Err without changing the timer's state. In this |
| /// case, the timer must be deregistered and re-registered. |
| </span><span class="kw">fn </span>extend_expiration(<span class="kw-2">&</span><span class="self">self</span>, new_timestamp: u64) -> <span class="prelude-ty">Result</span><(), ()> { |
| <span class="kw">let </span><span class="kw-2">mut </span>prior = <span class="self">self</span>.state.load(Ordering::Relaxed); |
| <span class="kw">loop </span>{ |
| <span class="kw">if </span>new_timestamp < prior || prior >= STATE_MIN_VALUE { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(()); |
| } |
| |
| <span class="kw">match </span><span class="self">self</span>.state.compare_exchange_weak( |
| prior, |
| new_timestamp, |
| Ordering::AcqRel, |
| Ordering::Acquire, |
| ) { |
| <span class="prelude-val">Ok</span>(<span class="kw">_</span>) => { |
| <span class="kw">return </span><span class="prelude-val">Ok</span>(()); |
| } |
| <span class="prelude-val">Err</span>(true_prior) => { |
| prior = true_prior; |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Returns true if the state of this timer indicates that the timer might |
| /// be registered with the driver. This check is performed with relaxed |
| /// ordering, but is conservative - if it returns false, the timer is |
| /// definitely _not_ registered. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>might_be_registered(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.state.load(Ordering::Relaxed) != u64::MAX |
| } |
| } |
| |
| <span class="doccomment">/// A timer entry. |
| /// |
| /// This is the handle to a timer that is controlled by the requester of the |
| /// timer. As this participates in intrusive data structures, it must be pinned |
| /// before polling. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>TimerEntry { |
| <span class="doccomment">/// Arc reference to the runtime handle. We can only free the driver after |
| /// deregistering everything from their respective timer wheels. |
| </span>driver: scheduler::Handle, |
| <span class="doccomment">/// Shared inner structure; this is part of an intrusive linked list, and |
| /// therefore other references can exist to it while mutable references to |
| /// Entry exist. |
| /// |
| /// This is manipulated only under the inner mutex. TODO: Can we use loom |
| /// cells for this? |
| </span>inner: StdUnsafeCell<TimerShared>, |
| <span class="doccomment">/// Initial deadline for the timer. This is used to register on the first |
| /// poll, as we can't register prior to being pinned. |
| </span>initial_deadline: <span class="prelude-ty">Option</span><Instant>, |
| <span class="doccomment">/// Ensure the type is !Unpin |
| </span>_m: std::marker::PhantomPinned, |
| } |
| |
| <span class="kw">unsafe impl </span>Send <span class="kw">for </span>TimerEntry {} |
| <span class="kw">unsafe impl </span>Sync <span class="kw">for </span>TimerEntry {} |
| |
| <span class="doccomment">/// An TimerHandle is the (non-enforced) "unique" pointer from the driver to the |
| /// timer entry. Generally, at most one TimerHandle exists for a timer at a time |
| /// (enforced by the timer state machine). |
| /// |
| /// SAFETY: An TimerHandle is essentially a raw pointer, and the usual caveats |
| /// of pointer safety apply. In particular, TimerHandle does not itself enforce |
| /// that the timer does still exist; however, normally an TimerHandle is created |
| /// immediately before registering the timer, and is consumed when firing the |
| /// timer, to help minimize mistakes. Still, because TimerHandle cannot enforce |
| /// memory safety, all operations are unsafe. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>TimerHandle { |
| inner: NonNull<TimerShared>, |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">type </span>EntryList = <span class="kw">crate</span>::util::linked_list::LinkedList<TimerShared, TimerShared>; |
| |
| <span class="doccomment">/// The shared state structure of a timer. This structure is shared between the |
| /// frontend (`Entry`) and driver backend. |
| /// |
| /// Note that this structure is located inside the `TimerEntry` structure. |
| </span><span class="attribute">#[derive(Debug)] |
| #[repr(C)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>TimerShared { |
| <span class="doccomment">/// Data manipulated by the driver thread itself, only. |
| </span>driver_state: CachePadded<TimerSharedPadded>, |
| |
| <span class="doccomment">/// Current state. This records whether the timer entry is currently under |
| /// the ownership of the driver, and if not, its current state (not |
| /// complete, fired, error, etc). |
| </span>state: StateCell, |
| |
| _p: PhantomPinned, |
| } |
| |
| <span class="macro">generate_addr_of_methods! </span>{ |
| <span class="kw">impl</span><> TimerShared { |
| <span class="kw">unsafe fn </span>addr_of_pointers(<span class="self">self</span>: NonNull<<span class="self">Self</span>>) -> NonNull<linked_list::Pointers<TimerShared>> { |
| <span class="kw-2">&</span><span class="self">self</span>.driver_state.<span class="number">0</span>.pointers |
| } |
| } |
| } |
| |
| <span class="kw">impl </span>TimerShared { |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new() -> <span class="self">Self </span>{ |
| <span class="self">Self </span>{ |
| state: StateCell::default(), |
| driver_state: CachePadded(TimerSharedPadded::new()), |
| _p: PhantomPinned, |
| } |
| } |
| |
| <span class="doccomment">/// Gets the cached time-of-expiration value. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>cached_when(<span class="kw-2">&</span><span class="self">self</span>) -> u64 { |
| <span class="comment">// Cached-when is only accessed under the driver lock, so we can use relaxed |
| </span><span class="self">self</span>.driver_state.<span class="number">0</span>.cached_when.load(Ordering::Relaxed) |
| } |
| |
| <span class="doccomment">/// Gets the true time-of-expiration value, and copies it into the cached |
| /// time-of-expiration value. |
| /// |
| /// SAFETY: Must be called with the driver lock held, and when this entry is |
| /// not in any timer wheel lists. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>sync_when(<span class="kw-2">&</span><span class="self">self</span>) -> u64 { |
| <span class="kw">let </span>true_when = <span class="self">self</span>.true_when(); |
| |
| <span class="self">self</span>.driver_state |
| .<span class="number">0 |
| </span>.cached_when |
| .store(true_when, Ordering::Relaxed); |
| |
| true_when |
| } |
| |
| <span class="doccomment">/// Sets the cached time-of-expiration value. |
| /// |
| /// SAFETY: Must be called with the driver lock held, and when this entry is |
| /// not in any timer wheel lists. |
| </span><span class="kw">unsafe fn </span>set_cached_when(<span class="kw-2">&</span><span class="self">self</span>, when: u64) { |
| <span class="self">self</span>.driver_state |
| .<span class="number">0 |
| </span>.cached_when |
| .store(when, Ordering::Relaxed); |
| } |
| |
| <span class="doccomment">/// Returns the true time-of-expiration value, with relaxed memory ordering. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>true_when(<span class="kw-2">&</span><span class="self">self</span>) -> u64 { |
| <span class="self">self</span>.state.when().expect(<span class="string">"Timer already fired"</span>) |
| } |
| |
| <span class="doccomment">/// Sets the true time-of-expiration value, even if it is less than the |
| /// current expiration or the timer is deregistered. |
| /// |
| /// SAFETY: Must only be called with the driver lock held and the entry not |
| /// in the timer wheel. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>set_expiration(<span class="kw-2">&</span><span class="self">self</span>, t: u64) { |
| <span class="self">self</span>.state.set_expiration(t); |
| <span class="self">self</span>.driver_state.<span class="number">0</span>.cached_when.store(t, Ordering::Relaxed); |
| } |
| |
| <span class="doccomment">/// Sets the true time-of-expiration only if it is after the current. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>extend_expiration(<span class="kw-2">&</span><span class="self">self</span>, t: u64) -> <span class="prelude-ty">Result</span><(), ()> { |
| <span class="self">self</span>.state.extend_expiration(t) |
| } |
| |
| <span class="doccomment">/// Returns a TimerHandle for this timer. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>handle(<span class="kw-2">&</span><span class="self">self</span>) -> TimerHandle { |
| TimerHandle { |
| inner: NonNull::from(<span class="self">self</span>), |
| } |
| } |
| |
| <span class="doccomment">/// Returns true if the state of this timer indicates that the timer might |
| /// be registered with the driver. This check is performed with relaxed |
| /// ordering, but is conservative - if it returns false, the timer is |
| /// definitely _not_ registered. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>might_be_registered(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.state.might_be_registered() |
| } |
| } |
| |
| <span class="doccomment">/// Additional shared state between the driver and the timer which is cache |
| /// padded. This contains the information that the driver thread accesses most |
| /// frequently to minimize contention. In particular, we move it away from the |
| /// waker, as the waker is updated on every poll. |
| </span><span class="kw">struct </span>TimerSharedPadded { |
| <span class="doccomment">/// A link within the doubly-linked list of timers on a particular level and |
| /// slot. Valid only if state is equal to Registered. |
| /// |
| /// Only accessed under the entry lock. |
| </span>pointers: linked_list::Pointers<TimerShared>, |
| |
| <span class="doccomment">/// The expiration time for which this entry is currently registered. |
| /// Generally owned by the driver, but is accessed by the entry when not |
| /// registered. |
| </span>cached_when: AtomicU64, |
| |
| <span class="doccomment">/// The true expiration time. Set by the timer future, read by the driver. |
| </span>true_when: AtomicU64, |
| } |
| |
| <span class="kw">impl </span>std::fmt::Debug <span class="kw">for </span>TimerSharedPadded { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>std::fmt::Formatter<<span class="lifetime">'_</span>>) -> std::fmt::Result { |
| f.debug_struct(<span class="string">"TimerSharedPadded"</span>) |
| .field(<span class="string">"when"</span>, <span class="kw-2">&</span><span class="self">self</span>.true_when.load(Ordering::Relaxed)) |
| .field(<span class="string">"cached_when"</span>, <span class="kw-2">&</span><span class="self">self</span>.cached_when.load(Ordering::Relaxed)) |
| .finish() |
| } |
| } |
| |
| <span class="kw">impl </span>TimerSharedPadded { |
| <span class="kw">fn </span>new() -> <span class="self">Self </span>{ |
| <span class="self">Self </span>{ |
| cached_when: AtomicU64::new(<span class="number">0</span>), |
| true_when: AtomicU64::new(<span class="number">0</span>), |
| pointers: linked_list::Pointers::new(), |
| } |
| } |
| } |
| |
| <span class="kw">unsafe impl </span>Send <span class="kw">for </span>TimerShared {} |
| <span class="kw">unsafe impl </span>Sync <span class="kw">for </span>TimerShared {} |
| |
| <span class="kw">unsafe impl </span>linked_list::Link <span class="kw">for </span>TimerShared { |
| <span class="kw">type </span>Handle = TimerHandle; |
| |
| <span class="kw">type </span>Target = TimerShared; |
| |
| <span class="kw">fn </span>as_raw(handle: <span class="kw-2">&</span><span class="self">Self</span>::Handle) -> NonNull<<span class="self">Self</span>::Target> { |
| handle.inner |
| } |
| |
| <span class="kw">unsafe fn </span>from_raw(ptr: NonNull<<span class="self">Self</span>::Target>) -> <span class="self">Self</span>::Handle { |
| TimerHandle { inner: ptr } |
| } |
| |
| <span class="kw">unsafe fn </span>pointers( |
| target: NonNull<<span class="self">Self</span>::Target>, |
| ) -> NonNull<linked_list::Pointers<<span class="self">Self</span>::Target>> { |
| TimerShared::addr_of_pointers(target) |
| } |
| } |
| |
| <span class="comment">// ===== impl Entry ===== |
| |
| </span><span class="kw">impl </span>TimerEntry { |
| <span class="attribute">#[track_caller] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new(handle: <span class="kw-2">&</span>scheduler::Handle, deadline: Instant) -> <span class="self">Self </span>{ |
| <span class="comment">// Panic if the time driver is not enabled |
| </span><span class="kw">let _ </span>= handle.driver().time(); |
| |
| <span class="kw">let </span>driver = handle.clone(); |
| |
| <span class="self">Self </span>{ |
| driver, |
| inner: StdUnsafeCell::new(TimerShared::new()), |
| initial_deadline: <span class="prelude-val">Some</span>(deadline), |
| _m: std::marker::PhantomPinned, |
| } |
| } |
| |
| <span class="kw">fn </span>inner(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>TimerShared { |
| <span class="kw">unsafe </span>{ <span class="kw-2">&*</span><span class="self">self</span>.inner.get() } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>is_elapsed(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| !<span class="self">self</span>.inner().state.might_be_registered() && <span class="self">self</span>.initial_deadline.is_none() |
| } |
| |
| <span class="doccomment">/// Cancels and deregisters the timer. This operation is irreversible. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>cancel(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) { |
| <span class="comment">// We need to perform an acq/rel fence with the driver thread, and the |
| // simplest way to do so is to grab the driver lock. |
| // |
| // Why is this necessary? We're about to release this timer's memory for |
| // some other non-timer use. However, we've been doing a bunch of |
| // relaxed (or even non-atomic) writes from the driver thread, and we'll |
| // be doing more from _this thread_ (as this memory is interpreted as |
| // something else). |
| // |
| // It is critical to ensure that, from the point of view of the driver, |
| // those future non-timer writes happen-after the timer is fully fired, |
| // and from the purpose of this thread, the driver's writes all |
| // happen-before we drop the timer. This in turn requires us to perform |
| // an acquire-release barrier in _both_ directions between the driver |
| // and dropping thread. |
| // |
| // The lock acquisition in clear_entry serves this purpose. All of the |
| // driver manipulations happen with the lock held, so we can just take |
| // the lock and be sure that this drop happens-after everything the |
| // driver did so far and happens-before everything the driver does in |
| // the future. While we have the lock held, we also go ahead and |
| // deregister the entry if necessary. |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.driver().clear_entry(NonNull::from(<span class="self">self</span>.inner())) }; |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>reset(<span class="kw-2">mut </span><span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>, new_time: Instant) { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.as_mut().get_unchecked_mut() }.initial_deadline = <span class="prelude-val">None</span>; |
| |
| <span class="kw">let </span>tick = <span class="self">self</span>.driver().time_source().deadline_to_tick(new_time); |
| |
| <span class="kw">if </span><span class="self">self</span>.inner().extend_expiration(tick).is_ok() { |
| <span class="kw">return</span>; |
| } |
| |
| <span class="kw">unsafe </span>{ |
| <span class="self">self</span>.driver() |
| .reregister(<span class="kw-2">&</span><span class="self">self</span>.driver.driver().io, tick, <span class="self">self</span>.inner().into()); |
| } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>poll_elapsed( |
| <span class="kw-2">mut </span><span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>, |
| cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>, |
| ) -> Poll<<span class="prelude-ty">Result</span><(), <span class="kw">super</span>::Error>> { |
| <span class="kw">if </span><span class="self">self</span>.driver().is_shutdown() { |
| <span class="macro">panic!</span>(<span class="string">"{}"</span>, <span class="kw">crate</span>::util::error::RUNTIME_SHUTTING_DOWN_ERROR); |
| } |
| |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(deadline) = <span class="self">self</span>.initial_deadline { |
| <span class="self">self</span>.as_mut().reset(deadline); |
| } |
| |
| <span class="kw">let </span>this = <span class="kw">unsafe </span>{ <span class="self">self</span>.get_unchecked_mut() }; |
| |
| this.inner().state.poll(cx.waker()) |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>driver(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span><span class="kw">super</span>::Handle { |
| <span class="self">self</span>.driver.driver().time() |
| } |
| } |
| |
| <span class="kw">impl </span>TimerHandle { |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>cached_when(<span class="kw-2">&</span><span class="self">self</span>) -> u64 { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.inner.as_ref().cached_when() } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>sync_when(<span class="kw-2">&</span><span class="self">self</span>) -> u64 { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.inner.as_ref().sync_when() } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>is_pending(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.inner.as_ref().state.is_pending() } |
| } |
| |
| <span class="doccomment">/// Forcibly sets the true and cached expiration times to the given tick. |
| /// |
| /// SAFETY: The caller must ensure that the handle remains valid, the driver |
| /// lock is held, and that the timer is not in any wheel linked lists. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>set_expiration(<span class="kw-2">&</span><span class="self">self</span>, tick: u64) { |
| <span class="self">self</span>.inner.as_ref().set_expiration(tick); |
| } |
| |
| <span class="doccomment">/// Attempts to mark this entry as pending. If the expiration time is after |
| /// `not_after`, however, returns an Err with the current expiration time. |
| /// |
| /// If an `Err` is returned, the `cached_when` value will be updated to this |
| /// new expiration time. |
| /// |
| /// SAFETY: The caller must ensure that the handle remains valid, the driver |
| /// lock is held, and that the timer is not in any wheel linked lists. |
| /// After returning Ok, the entry must be added to the pending list. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>mark_pending(<span class="kw-2">&</span><span class="self">self</span>, not_after: u64) -> <span class="prelude-ty">Result</span><(), u64> { |
| <span class="kw">match </span><span class="self">self</span>.inner.as_ref().state.mark_pending(not_after) { |
| <span class="prelude-val">Ok</span>(()) => { |
| <span class="comment">// mark this as being on the pending queue in cached_when |
| </span><span class="self">self</span>.inner.as_ref().set_cached_when(u64::MAX); |
| <span class="prelude-val">Ok</span>(()) |
| } |
| <span class="prelude-val">Err</span>(tick) => { |
| <span class="self">self</span>.inner.as_ref().set_cached_when(tick); |
| <span class="prelude-val">Err</span>(tick) |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Attempts to transition to a terminal state. If the state is already a |
| /// terminal state, does nothing. |
| /// |
| /// Because the entry might be dropped after the state is moved to a |
| /// terminal state, this function consumes the handle to ensure we don't |
| /// access the entry afterwards. |
| /// |
| /// Returns the last-registered waker, if any. |
| /// |
| /// SAFETY: The driver lock must be held while invoking this function, and |
| /// the entry must not be in any wheel linked lists. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>fire(<span class="self">self</span>, completed_state: TimerResult) -> <span class="prelude-ty">Option</span><Waker> { |
| <span class="self">self</span>.inner.as_ref().state.fire(completed_state) |
| } |
| } |
| |
| <span class="kw">impl </span>Drop <span class="kw">for </span>TimerEntry { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">unsafe </span>{ Pin::new_unchecked(<span class="self">self</span>) }.as_mut().cancel() |
| } |
| } |
| |
| <span class="comment">// Copied from [crossbeam/cache_padded](https://github.com/crossbeam-rs/crossbeam/blob/fa35346b7c789bba045ad789e894c68c466d1779/crossbeam-utils/src/cache_padded.rs#L62-L127) |
| // |
| // Starting from Intel's Sandy Bridge, spatial prefetcher is now pulling pairs of 64-byte cache |
| // lines at a time, so we have to align to 128 bytes rather than 64. |
| // |
| // Sources: |
| // - https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf |
| // - https://github.com/facebook/folly/blob/1b5288e6eea6df074758f877c849b6e73bbb9fbb/folly/lang/Align.h#L107 |
| // |
| // ARM's big.LITTLE architecture has asymmetric cores and "big" cores have 128-byte cache line size. |
| // |
| // Sources: |
| // - https://www.mono-project.com/news/2016/09/12/arm64-icache/ |
| // |
| // powerpc64 has 128-byte cache line size. |
| // |
| // Sources: |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_ppc64x.go#L9 |
| </span><span class="attribute">#[cfg_attr( |
| any( |
| target_arch = <span class="string">"x86_64"</span>, |
| target_arch = <span class="string">"aarch64"</span>, |
| target_arch = <span class="string">"powerpc64"</span>, |
| ), |
| repr(align(<span class="number">128</span>)) |
| )] |
| </span><span class="comment">// arm, mips, mips64, and riscv64 have 32-byte cache line size. |
| // |
| // Sources: |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_arm.go#L7 |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips.go#L7 |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mipsle.go#L7 |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips64x.go#L9 |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_riscv64.go#L7 |
| </span><span class="attribute">#[cfg_attr( |
| any( |
| target_arch = <span class="string">"arm"</span>, |
| target_arch = <span class="string">"mips"</span>, |
| target_arch = <span class="string">"mips64"</span>, |
| target_arch = <span class="string">"riscv64"</span>, |
| ), |
| repr(align(<span class="number">32</span>)) |
| )] |
| </span><span class="comment">// s390x has 256-byte cache line size. |
| // |
| // Sources: |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_s390x.go#L7 |
| </span><span class="attribute">#[cfg_attr(target_arch = <span class="string">"s390x"</span>, repr(align(<span class="number">256</span>)))] |
| </span><span class="comment">// x86 and wasm have 64-byte cache line size. |
| // |
| // Sources: |
| // - https://github.com/golang/go/blob/dda2991c2ea0c5914714469c4defc2562a907230/src/internal/cpu/cpu_x86.go#L9 |
| // - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_wasm.go#L7 |
| // |
| // All others are assumed to have 64-byte cache line size. |
| </span><span class="attribute">#[cfg_attr( |
| not(any( |
| target_arch = <span class="string">"x86_64"</span>, |
| target_arch = <span class="string">"aarch64"</span>, |
| target_arch = <span class="string">"powerpc64"</span>, |
| target_arch = <span class="string">"arm"</span>, |
| target_arch = <span class="string">"mips"</span>, |
| target_arch = <span class="string">"mips64"</span>, |
| target_arch = <span class="string">"riscv64"</span>, |
| target_arch = <span class="string">"s390x"</span>, |
| )), |
| repr(align(<span class="number">64</span>)) |
| )] |
| #[derive(Debug, Default)] |
| </span><span class="kw">struct </span>CachePadded<T>(T); |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../../" data-current-crate="tokio" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
