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</pre><pre class="rust">
<span class="doccomment">//! The global data and participant for garbage collection.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Registration</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! In order to track all participants in one place, we need some form of participant</span>
<span class="doccomment">//! registration. When a participant is created, it is registered to a global lock-free</span>
<span class="doccomment">//! singly-linked list of registries; and when a participant is leaving, it is unregistered from the</span>
<span class="doccomment">//! list.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Pinning</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Every participant contains an integer that tells whether the participant is pinned and if so,</span>
<span class="doccomment">//! what was the global epoch at the time it was pinned. Participants also hold a pin counter that</span>
<span class="doccomment">//! aids in periodic global epoch advancement.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! When a participant is pinned, a `Guard` is returned as a witness that the participant is pinned.</span>
<span class="doccomment">//! Guards are necessary for performing atomic operations, and for freeing/dropping locations.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Thread-local bag</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Objects that get unlinked from concurrent data structures must be stashed away until the global</span>
<span class="doccomment">//! epoch sufficiently advances so that they become safe for destruction. Pointers to such objects</span>
<span class="doccomment">//! are pushed into a thread-local bag, and when it becomes full, the bag is marked with the current</span>
<span class="doccomment">//! global epoch and pushed into the global queue of bags. We store objects in thread-local storages</span>
<span class="doccomment">//! for amortizing the synchronization cost of pushing the garbages to a global queue.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Global queue</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Whenever a bag is pushed into a queue, the objects in some bags in the queue are collected and</span>
<span class="doccomment">//! destroyed along the way. This design reduces contention on data structures. The global queue</span>
<span class="doccomment">//! cannot be explicitly accessed: the only way to interact with it is by calling functions</span>
<span class="doccomment">//! `defer()` that adds an object to the thread-local bag, or `collect()` that manually triggers</span>
<span class="doccomment">//! garbage collection.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Ideally each instance of concurrent data structure may have its own queue that gets fully</span>
<span class="doccomment">//! destroyed as soon as the data structure gets dropped.</span>
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::primitive::cell::UnsafeCell</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::primitive::sync::atomic</span>;
<span class="kw">use</span> <span class="ident">core::cell::Cell</span>;
<span class="kw">use</span> <span class="ident">core::mem</span>::{<span class="self">self</span>, <span class="ident">ManuallyDrop</span>};
<span class="kw">use</span> <span class="ident">core::num::Wrapping</span>;
<span class="kw">use</span> <span class="ident">core::sync::atomic::Ordering</span>;
<span class="kw">use</span> <span class="ident">core</span>::{<span class="ident">fmt</span>, <span class="ident">ptr</span>};
<span class="kw">use</span> <span class="ident">crossbeam_utils::CachePadded</span>;
<span class="kw">use</span> <span class="ident">memoffset::offset_of</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::atomic</span>::{<span class="ident">Owned</span>, <span class="ident">Shared</span>};
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::collector</span>::{<span class="ident">Collector</span>, <span class="ident">LocalHandle</span>};
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::deferred::Deferred</span>;
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::epoch</span>::{<span class="ident">AtomicEpoch</span>, <span class="ident">Epoch</span>};
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::guard</span>::{<span class="ident">unprotected</span>, <span class="ident">Guard</span>};
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::sync::list</span>::{<span class="ident">Entry</span>, <span class="ident">IsElement</span>, <span class="ident">IterError</span>, <span class="ident">List</span>};
<span class="kw">use</span> <span class="kw">crate</span><span class="ident">::sync::queue::Queue</span>;
<span class="doccomment">/// Maximum number of objects a bag can contain.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">crossbeam_sanitize</span>))]</span>
<span class="kw">const</span> <span class="ident">MAX_OBJECTS</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">62</span>;
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">crossbeam_sanitize</span>)]</span>
<span class="kw">const</span> <span class="ident">MAX_OBJECTS</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">4</span>;
<span class="doccomment">/// A bag of deferred functions.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct</span> <span class="ident">Bag</span> {
<span class="doccomment">/// Stashed objects.</span>
<span class="ident">deferreds</span>: [<span class="ident">Deferred</span>; <span class="ident">MAX_OBJECTS</span>],
<span class="ident">len</span>: <span class="ident">usize</span>,
}
<span class="doccomment">/// `Bag::try_push()` requires that it is safe for another thread to execute the given functions.</span>
<span class="kw">unsafe</span> <span class="kw">impl</span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">Bag</span> {}
<span class="kw">impl</span> <span class="ident">Bag</span> {
<span class="doccomment">/// Returns a new, empty bag.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="self">Self</span><span class="ident">::default</span>()
}
<span class="doccomment">/// Returns `true` if the bag is empty.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">is_empty</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="self">self</span>.<span class="ident">len</span> <span class="op">=</span><span class="op">=</span> <span class="number">0</span>
}
<span class="doccomment">/// Attempts to insert a deferred function into the bag.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `Ok(())` if successful, and `Err(deferred)` for the given `deferred` if the bag is</span>
<span class="doccomment">/// full.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// It should be safe for another thread to execute the given function.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">try_push</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">deferred</span>: <span class="ident">Deferred</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Deferred</span><span class="op">></span> {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">len</span> <span class="op"><</span> <span class="ident">MAX_OBJECTS</span> {
<span class="self">self</span>.<span class="ident">deferreds</span>[<span class="self">self</span>.<span class="ident">len</span>] <span class="op">=</span> <span class="ident">deferred</span>;
<span class="self">self</span>.<span class="ident">len</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
<span class="prelude-val">Ok</span>(())
} <span class="kw">else</span> {
<span class="prelude-val">Err</span>(<span class="ident">deferred</span>)
}
}
<span class="doccomment">/// Seals the bag with the given epoch.</span>
<span class="kw">fn</span> <span class="ident">seal</span>(<span class="self">self</span>, <span class="ident">epoch</span>: <span class="ident">Epoch</span>) <span class="op">-</span><span class="op">></span> <span class="ident">SealedBag</span> {
<span class="ident">SealedBag</span> { <span class="ident">epoch</span>, <span class="ident">bag</span>: <span class="self">self</span> }
}
}
<span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">Bag</span> {
<span class="attribute">#[<span class="ident">rustfmt::skip</span>]</span>
<span class="kw">fn</span> <span class="ident">default</span>() <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="comment">// TODO: [no_op; MAX_OBJECTS] syntax blocked by https://github.com/rust-lang/rust/issues/49147</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">crossbeam_sanitize</span>))]</span>
<span class="kw">return</span> <span class="ident">Bag</span> {
<span class="ident">len</span>: <span class="number">0</span>,
<span class="ident">deferreds</span>: [
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
],
};
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">crossbeam_sanitize</span>)]</span>
<span class="kw">return</span> <span class="ident">Bag</span> {
<span class="ident">len</span>: <span class="number">0</span>,
<span class="ident">deferreds</span>: [
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
<span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>),
],
};
}
}
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Bag</span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="comment">// Call all deferred functions.</span>
<span class="kw">for</span> <span class="ident">deferred</span> <span class="kw">in</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">deferreds</span>[..<span class="self">self</span>.<span class="ident">len</span>] {
<span class="kw">let</span> <span class="ident">no_op</span> <span class="op">=</span> <span class="ident">Deferred::new</span>(<span class="ident">no_op_func</span>);
<span class="kw">let</span> <span class="ident">owned_deferred</span> <span class="op">=</span> <span class="ident">mem::replace</span>(<span class="ident">deferred</span>, <span class="ident">no_op</span>);
<span class="ident">owned_deferred</span>.<span class="ident">call</span>();
}
}
}
<span class="comment">// can't #[derive(Debug)] because Debug is not implemented for arrays 64 items long</span>
<span class="kw">impl</span> <span class="ident">fmt::Debug</span> <span class="kw">for</span> <span class="ident">Bag</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt::Formatter</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">fmt::Result</span> {
<span class="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"Bag"</span>)
.<span class="ident">field</span>(<span class="string">"deferreds"</span>, <span class="op">&&</span><span class="self">self</span>.<span class="ident">deferreds</span>[..<span class="self">self</span>.<span class="ident">len</span>])
.<span class="ident">finish</span>()
}
}
<span class="kw">fn</span> <span class="ident">no_op_func</span>() {}
<span class="doccomment">/// A pair of an epoch and a bag.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Default</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">SealedBag</span> {
<span class="ident">epoch</span>: <span class="ident">Epoch</span>,
<span class="ident">bag</span>: <span class="ident">Bag</span>,
}
<span class="doccomment">/// It is safe to share `SealedBag` because `is_expired` only inspects the epoch.</span>
<span class="kw">unsafe</span> <span class="kw">impl</span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">SealedBag</span> {}
<span class="kw">impl</span> <span class="ident">SealedBag</span> {
<span class="doccomment">/// Checks if it is safe to drop the bag w.r.t. the given global epoch.</span>
<span class="kw">fn</span> <span class="ident">is_expired</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">global_epoch</span>: <span class="ident">Epoch</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="comment">// A pinned participant can witness at most one epoch advancement. Therefore, any bag that</span>
<span class="comment">// is within one epoch of the current one cannot be destroyed yet.</span>
<span class="ident">global_epoch</span>.<span class="ident">wrapping_sub</span>(<span class="self">self</span>.<span class="ident">epoch</span>) <span class="op">></span><span class="op">=</span> <span class="number">2</span>
}
}
<span class="doccomment">/// The global data for a garbage collector.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct</span> <span class="ident">Global</span> {
<span class="doccomment">/// The intrusive linked list of `Local`s.</span>
<span class="ident">locals</span>: <span class="ident">List</span><span class="op"><</span><span class="ident">Local</span><span class="op">></span>,
<span class="doccomment">/// The global queue of bags of deferred functions.</span>
<span class="ident">queue</span>: <span class="ident">Queue</span><span class="op"><</span><span class="ident">SealedBag</span><span class="op">></span>,
<span class="doccomment">/// The global epoch.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="ident">epoch</span>: <span class="ident">CachePadded</span><span class="op"><</span><span class="ident">AtomicEpoch</span><span class="op">></span>,
}
<span class="kw">impl</span> <span class="ident">Global</span> {
<span class="doccomment">/// Number of bags to destroy.</span>
<span class="kw">const</span> <span class="ident">COLLECT_STEPS</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">8</span>;
<span class="doccomment">/// Creates a new global data for garbage collection.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="self">Self</span> {
<span class="ident">locals</span>: <span class="ident">List::new</span>(),
<span class="ident">queue</span>: <span class="ident">Queue::new</span>(),
<span class="ident">epoch</span>: <span class="ident">CachePadded::new</span>(<span class="ident">AtomicEpoch::new</span>(<span class="ident">Epoch::starting</span>())),
}
}
<span class="doccomment">/// Pushes the bag into the global queue and replaces the bag with a new empty bag.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">push_bag</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">bag</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">Bag</span>, <span class="ident">guard</span>: <span class="kw-2">&</span><span class="ident">Guard</span>) {
<span class="kw">let</span> <span class="ident">bag</span> <span class="op">=</span> <span class="ident">mem::replace</span>(<span class="ident">bag</span>, <span class="ident">Bag::new</span>());
<span class="ident">atomic::fence</span>(<span class="ident">Ordering::SeqCst</span>);
<span class="kw">let</span> <span class="ident">epoch</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>);
<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">push</span>(<span class="ident">bag</span>.<span class="ident">seal</span>(<span class="ident">epoch</span>), <span class="ident">guard</span>);
}
<span class="doccomment">/// Collects several bags from the global queue and executes deferred functions in them.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note: This may itself produce garbage and in turn allocate new bags.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `pin()` rarely calls `collect()`, so we want the compiler to place that call on a cold</span>
<span class="doccomment">/// path. In other words, we want the compiler to optimize branching for the case when</span>
<span class="doccomment">/// `collect()` is not called.</span>
<span class="attribute">#[<span class="ident">cold</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">collect</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">guard</span>: <span class="kw-2">&</span><span class="ident">Guard</span>) {
<span class="kw">let</span> <span class="ident">global_epoch</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">try_advance</span>(<span class="ident">guard</span>);
<span class="kw">let</span> <span class="ident">steps</span> <span class="op">=</span> <span class="kw">if</span> <span class="macro">cfg!</span>(<span class="ident">crossbeam_sanitize</span>) {
<span class="ident">usize::max_value</span>()
} <span class="kw">else</span> {
<span class="self">Self</span><span class="ident">::COLLECT_STEPS</span>
};
<span class="kw">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..<span class="ident">steps</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">try_pop_if</span>(
<span class="kw-2">&</span><span class="op">|</span><span class="ident">sealed_bag</span>: <span class="kw-2">&</span><span class="ident">SealedBag</span><span class="op">|</span> <span class="ident">sealed_bag</span>.<span class="ident">is_expired</span>(<span class="ident">global_epoch</span>),
<span class="ident">guard</span>,
) {
<span class="prelude-val">None</span> <span class="op">=</span><span class="op">></span> <span class="kw">break</span>,
<span class="prelude-val">Some</span>(<span class="ident">sealed_bag</span>) <span class="op">=</span><span class="op">></span> <span class="ident">drop</span>(<span class="ident">sealed_bag</span>),
}
}
}
<span class="doccomment">/// Attempts to advance the global epoch.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The global epoch can advance only if all currently pinned participants have been pinned in</span>
<span class="doccomment">/// the current epoch.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns the current global epoch.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// `try_advance()` is annotated `#[cold]` because it is rarely called.</span>
<span class="attribute">#[<span class="ident">cold</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">try_advance</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">guard</span>: <span class="kw-2">&</span><span class="ident">Guard</span>) <span class="op">-</span><span class="op">></span> <span class="ident">Epoch</span> {
<span class="kw">let</span> <span class="ident">global_epoch</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>);
<span class="ident">atomic::fence</span>(<span class="ident">Ordering::SeqCst</span>);
<span class="comment">// TODO(stjepang): `Local`s are stored in a linked list because linked lists are fairly</span>
<span class="comment">// easy to implement in a lock-free manner. However, traversal can be slow due to cache</span>
<span class="comment">// misses and data dependencies. We should experiment with other data structures as well.</span>
<span class="kw">for</span> <span class="ident">local</span> <span class="kw">in</span> <span class="self">self</span>.<span class="ident">locals</span>.<span class="ident">iter</span>(<span class="kw-2">&</span><span class="ident">guard</span>) {
<span class="kw">match</span> <span class="ident">local</span> {
<span class="prelude-val">Err</span>(<span class="ident">IterError::Stalled</span>) <span class="op">=</span><span class="op">></span> {
<span class="comment">// A concurrent thread stalled this iteration. That thread might also try to</span>
<span class="comment">// advance the epoch, in which case we leave the job to it. Otherwise, the</span>
<span class="comment">// epoch will not be advanced.</span>
<span class="kw">return</span> <span class="ident">global_epoch</span>;
}
<span class="prelude-val">Ok</span>(<span class="ident">local</span>) <span class="op">=</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">local_epoch</span> <span class="op">=</span> <span class="ident">local</span>.<span class="ident">epoch</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>);
<span class="comment">// If the participant was pinned in a different epoch, we cannot advance the</span>
<span class="comment">// global epoch just yet.</span>
<span class="kw">if</span> <span class="ident">local_epoch</span>.<span class="ident">is_pinned</span>() <span class="op">&&</span> <span class="ident">local_epoch</span>.<span class="ident">unpinned</span>() <span class="op">!</span><span class="op">=</span> <span class="ident">global_epoch</span> {
<span class="kw">return</span> <span class="ident">global_epoch</span>;
}
}
}
}
<span class="ident">atomic::fence</span>(<span class="ident">Ordering::Acquire</span>);
<span class="comment">// All pinned participants were pinned in the current global epoch.</span>
<span class="comment">// Now let's advance the global epoch...</span>
<span class="comment">//</span>
<span class="comment">// Note that if another thread already advanced it before us, this store will simply</span>
<span class="comment">// overwrite the global epoch with the same value. This is true because `try_advance` was</span>
<span class="comment">// called from a thread that was pinned in `global_epoch`, and the global epoch cannot be</span>
<span class="comment">// advanced two steps ahead of it.</span>
<span class="kw">let</span> <span class="ident">new_epoch</span> <span class="op">=</span> <span class="ident">global_epoch</span>.<span class="ident">successor</span>();
<span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">store</span>(<span class="ident">new_epoch</span>, <span class="ident">Ordering::Release</span>);
<span class="ident">new_epoch</span>
}
}
<span class="doccomment">/// Participant for garbage collection.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct</span> <span class="ident">Local</span> {
<span class="doccomment">/// A node in the intrusive linked list of `Local`s.</span>
<span class="ident">entry</span>: <span class="ident">Entry</span>,
<span class="doccomment">/// The local epoch.</span>
<span class="ident">epoch</span>: <span class="ident">AtomicEpoch</span>,
<span class="doccomment">/// A reference to the global data.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When all guards and handles get dropped, this reference is destroyed.</span>
<span class="ident">collector</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">ManuallyDrop</span><span class="op"><</span><span class="ident">Collector</span><span class="op">></span><span class="op">></span>,
<span class="doccomment">/// The local bag of deferred functions.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="ident">bag</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">Bag</span><span class="op">></span>,
<span class="doccomment">/// The number of guards keeping this participant pinned.</span>
<span class="ident">guard_count</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>,
<span class="doccomment">/// The number of active handles.</span>
<span class="ident">handle_count</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>,
<span class="doccomment">/// Total number of pinnings performed.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is just an auxiliary counter that sometimes kicks off collection.</span>
<span class="ident">pin_count</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">Wrapping</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span><span class="op">></span>,
}
<span class="comment">// Make sure `Local` is less than or equal to 2048 bytes.</span>
<span class="comment">// https://github.com/crossbeam-rs/crossbeam/issues/551</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">not</span>(<span class="ident">crossbeam_sanitize</span>))]</span> <span class="comment">// `crossbeam_sanitize` reduces the size of `Local`</span>
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">local_size</span>() {
<span class="macro">assert!</span>(
<span class="ident">core::mem::size_of</span>::<span class="op"><</span><span class="ident">Local</span><span class="op">></span>() <span class="op"><</span><span class="op">=</span> <span class="number">2048</span>,
<span class="string">"An allocation of `Local` should be <= 2048 bytes."</span>
);
}
<span class="kw">impl</span> <span class="ident">Local</span> {
<span class="doccomment">/// Number of pinnings after which a participant will execute some deferred functions from the</span>
<span class="doccomment">/// global queue.</span>
<span class="kw">const</span> <span class="ident">PINNINGS_BETWEEN_COLLECT</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">128</span>;
<span class="doccomment">/// Registers a new `Local` in the provided `Global`.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">register</span>(<span class="ident">collector</span>: <span class="kw-2">&</span><span class="ident">Collector</span>) <span class="op">-</span><span class="op">></span> <span class="ident">LocalHandle</span> {
<span class="kw">unsafe</span> {
<span class="comment">// Since we dereference no pointers in this block, it is safe to use `unprotected`.</span>
<span class="kw">let</span> <span class="ident">local</span> <span class="op">=</span> <span class="ident">Owned::new</span>(<span class="ident">Local</span> {
<span class="ident">entry</span>: <span class="ident">Entry::default</span>(),
<span class="ident">epoch</span>: <span class="ident">AtomicEpoch::new</span>(<span class="ident">Epoch::starting</span>()),
<span class="ident">collector</span>: <span class="ident">UnsafeCell::new</span>(<span class="ident">ManuallyDrop::new</span>(<span class="ident">collector</span>.<span class="ident">clone</span>())),
<span class="ident">bag</span>: <span class="ident">UnsafeCell::new</span>(<span class="ident">Bag::new</span>()),
<span class="ident">guard_count</span>: <span class="ident">Cell::new</span>(<span class="number">0</span>),
<span class="ident">handle_count</span>: <span class="ident">Cell::new</span>(<span class="number">1</span>),
<span class="ident">pin_count</span>: <span class="ident">Cell::new</span>(<span class="ident">Wrapping</span>(<span class="number">0</span>)),
})
.<span class="ident">into_shared</span>(<span class="ident">unprotected</span>());
<span class="ident">collector</span>.<span class="ident">global</span>.<span class="ident">locals</span>.<span class="ident">insert</span>(<span class="ident">local</span>, <span class="ident">unprotected</span>());
<span class="ident">LocalHandle</span> {
<span class="ident">local</span>: <span class="ident">local</span>.<span class="ident">as_raw</span>(),
}
}
}
<span class="doccomment">/// Returns a reference to the `Global` in which this `Local` resides.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">global</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">Global</span> {
<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">collector</span>().<span class="ident">global</span>
}
<span class="doccomment">/// Returns a reference to the `Collector` in which this `Local` resides.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">collector</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">Collector</span> {
<span class="self">self</span>.<span class="ident">collector</span>.<span class="ident">with</span>(<span class="op">|</span><span class="ident">c</span><span class="op">|</span> <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="ident">c</span> })
}
<span class="doccomment">/// Returns `true` if the current participant is pinned.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">is_pinned</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">get</span>() <span class="op">></span> <span class="number">0</span>
}
<span class="doccomment">/// Adds `deferred` to the thread-local bag.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// It should be safe for another thread to execute the given function.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">defer</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="kw-2">mut</span> <span class="ident">deferred</span>: <span class="ident">Deferred</span>, <span class="ident">guard</span>: <span class="kw-2">&</span><span class="ident">Guard</span>) {
<span class="kw">let</span> <span class="ident">bag</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bag</span>.<span class="ident">with_mut</span>(<span class="op">|</span><span class="ident">b</span><span class="op">|</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">b</span>);
<span class="kw">while</span> <span class="kw">let</span> <span class="prelude-val">Err</span>(<span class="ident">d</span>) <span class="op">=</span> <span class="ident">bag</span>.<span class="ident">try_push</span>(<span class="ident">deferred</span>) {
<span class="self">self</span>.<span class="ident">global</span>().<span class="ident">push_bag</span>(<span class="ident">bag</span>, <span class="ident">guard</span>);
<span class="ident">deferred</span> <span class="op">=</span> <span class="ident">d</span>;
}
}
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">flush</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">guard</span>: <span class="kw-2">&</span><span class="ident">Guard</span>) {
<span class="kw">let</span> <span class="ident">bag</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">bag</span>.<span class="ident">with_mut</span>(<span class="op">|</span><span class="ident">b</span><span class="op">|</span> <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">b</span> });
<span class="kw">if</span> <span class="op">!</span><span class="ident">bag</span>.<span class="ident">is_empty</span>() {
<span class="self">self</span>.<span class="ident">global</span>().<span class="ident">push_bag</span>(<span class="ident">bag</span>, <span class="ident">guard</span>);
}
<span class="self">self</span>.<span class="ident">global</span>().<span class="ident">collect</span>(<span class="ident">guard</span>);
}
<span class="doccomment">/// Pins the `Local`.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">pin</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">Guard</span> {
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="ident">Guard</span> { <span class="ident">local</span>: <span class="self">self</span> };
<span class="kw">let</span> <span class="ident">guard_count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">get</span>();
<span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">set</span>(<span class="ident">guard_count</span>.<span class="ident">checked_add</span>(<span class="number">1</span>).<span class="ident">unwrap</span>());
<span class="kw">if</span> <span class="ident">guard_count</span> <span class="op">=</span><span class="op">=</span> <span class="number">0</span> {
<span class="kw">let</span> <span class="ident">global_epoch</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">global</span>().<span class="ident">epoch</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>);
<span class="kw">let</span> <span class="ident">new_epoch</span> <span class="op">=</span> <span class="ident">global_epoch</span>.<span class="ident">pinned</span>();
<span class="comment">// Now we must store `new_epoch` into `self.epoch` and execute a `SeqCst` fence.</span>
<span class="comment">// The fence makes sure that any future loads from `Atomic`s will not happen before</span>
<span class="comment">// this store.</span>
<span class="kw">if</span> <span class="macro">cfg!</span>(<span class="ident">any</span>(<span class="ident">target_arch</span> <span class="op">=</span> <span class="string">"x86"</span>, <span class="ident">target_arch</span> <span class="op">=</span> <span class="string">"x86_64"</span>)) {
<span class="comment">// HACK(stjepang): On x86 architectures there are two different ways of executing</span>
<span class="comment">// a `SeqCst` fence.</span>
<span class="comment">//</span>
<span class="comment">// 1. `atomic::fence(SeqCst)`, which compiles into a `mfence` instruction.</span>
<span class="comment">// 2. `_.compare_exchange(_, _, SeqCst, SeqCst)`, which compiles into a `lock cmpxchg`</span>
<span class="comment">// instruction.</span>
<span class="comment">//</span>
<span class="comment">// Both instructions have the effect of a full barrier, but benchmarks have shown</span>
<span class="comment">// that the second one makes pinning faster in this particular case. It is not</span>
<span class="comment">// clear that this is permitted by the C++ memory model (SC fences work very</span>
<span class="comment">// differently from SC accesses), but experimental evidence suggests that this</span>
<span class="comment">// works fine. Using inline assembly would be a viable (and correct) alternative,</span>
<span class="comment">// but alas, that is not possible on stable Rust.</span>
<span class="kw">let</span> <span class="ident">current</span> <span class="op">=</span> <span class="ident">Epoch::starting</span>();
<span class="kw">let</span> <span class="ident">res</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">compare_exchange</span>(
<span class="ident">current</span>,
<span class="ident">new_epoch</span>,
<span class="ident">Ordering::SeqCst</span>,
<span class="ident">Ordering::SeqCst</span>,
);
<span class="macro">debug_assert!</span>(<span class="ident">res</span>.<span class="ident">is_ok</span>(), <span class="string">"participant was expected to be unpinned"</span>);
<span class="comment">// We add a compiler fence to make it less likely for LLVM to do something wrong</span>
<span class="comment">// here. Formally, this is not enough to get rid of data races; practically,</span>
<span class="comment">// it should go a long way.</span>
<span class="ident">atomic::compiler_fence</span>(<span class="ident">Ordering::SeqCst</span>);
} <span class="kw">else</span> {
<span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">store</span>(<span class="ident">new_epoch</span>, <span class="ident">Ordering::Relaxed</span>);
<span class="ident">atomic::fence</span>(<span class="ident">Ordering::SeqCst</span>);
}
<span class="comment">// Increment the pin counter.</span>
<span class="kw">let</span> <span class="ident">count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">pin_count</span>.<span class="ident">get</span>();
<span class="self">self</span>.<span class="ident">pin_count</span>.<span class="ident">set</span>(<span class="ident">count</span> <span class="op">+</span> <span class="ident">Wrapping</span>(<span class="number">1</span>));
<span class="comment">// After every `PINNINGS_BETWEEN_COLLECT` try advancing the epoch and collecting</span>
<span class="comment">// some garbage.</span>
<span class="kw">if</span> <span class="ident">count</span>.<span class="number">0</span> <span class="op">%</span> <span class="self">Self</span><span class="ident">::PINNINGS_BETWEEN_COLLECT</span> <span class="op">=</span><span class="op">=</span> <span class="number">0</span> {
<span class="self">self</span>.<span class="ident">global</span>().<span class="ident">collect</span>(<span class="kw-2">&</span><span class="ident">guard</span>);
}
}
<span class="ident">guard</span>
}
<span class="doccomment">/// Unpins the `Local`.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">unpin</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let</span> <span class="ident">guard_count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">get</span>();
<span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">set</span>(<span class="ident">guard_count</span> <span class="op">-</span> <span class="number">1</span>);
<span class="kw">if</span> <span class="ident">guard_count</span> <span class="op">=</span><span class="op">=</span> <span class="number">1</span> {
<span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">store</span>(<span class="ident">Epoch::starting</span>(), <span class="ident">Ordering::Release</span>);
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">get</span>() <span class="op">=</span><span class="op">=</span> <span class="number">0</span> {
<span class="self">self</span>.<span class="ident">finalize</span>();
}
}
}
<span class="doccomment">/// Unpins and then pins the `Local`.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">repin</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let</span> <span class="ident">guard_count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">get</span>();
<span class="comment">// Update the local epoch only if there's only one guard.</span>
<span class="kw">if</span> <span class="ident">guard_count</span> <span class="op">=</span><span class="op">=</span> <span class="number">1</span> {
<span class="kw">let</span> <span class="ident">epoch</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>);
<span class="kw">let</span> <span class="ident">global_epoch</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">global</span>().<span class="ident">epoch</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>).<span class="ident">pinned</span>();
<span class="comment">// Update the local epoch only if the global epoch is greater than the local epoch.</span>
<span class="kw">if</span> <span class="ident">epoch</span> <span class="op">!</span><span class="op">=</span> <span class="ident">global_epoch</span> {
<span class="comment">// We store the new epoch with `Release` because we need to ensure any memory</span>
<span class="comment">// accesses from the previous epoch do not leak into the new one.</span>
<span class="self">self</span>.<span class="ident">epoch</span>.<span class="ident">store</span>(<span class="ident">global_epoch</span>, <span class="ident">Ordering::Release</span>);
<span class="comment">// However, we don't need a following `SeqCst` fence, because it is safe for memory</span>
<span class="comment">// accesses from the new epoch to be executed before updating the local epoch. At</span>
<span class="comment">// worse, other threads will see the new epoch late and delay GC slightly.</span>
}
}
}
<span class="doccomment">/// Increments the handle count.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">acquire_handle</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let</span> <span class="ident">handle_count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">get</span>();
<span class="macro">debug_assert!</span>(<span class="ident">handle_count</span> <span class="op">></span><span class="op">=</span> <span class="number">1</span>);
<span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">set</span>(<span class="ident">handle_count</span> <span class="op">+</span> <span class="number">1</span>);
}
<span class="doccomment">/// Decrements the handle count.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">release_handle</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let</span> <span class="ident">guard_count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">get</span>();
<span class="kw">let</span> <span class="ident">handle_count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">get</span>();
<span class="macro">debug_assert!</span>(<span class="ident">handle_count</span> <span class="op">></span><span class="op">=</span> <span class="number">1</span>);
<span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">set</span>(<span class="ident">handle_count</span> <span class="op">-</span> <span class="number">1</span>);
<span class="kw">if</span> <span class="ident">guard_count</span> <span class="op">=</span><span class="op">=</span> <span class="number">0</span> <span class="op">&&</span> <span class="ident">handle_count</span> <span class="op">=</span><span class="op">=</span> <span class="number">1</span> {
<span class="self">self</span>.<span class="ident">finalize</span>();
}
}
<span class="doccomment">/// Removes the `Local` from the global linked list.</span>
<span class="attribute">#[<span class="ident">cold</span>]</span>
<span class="kw">fn</span> <span class="ident">finalize</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="macro">debug_assert_eq!</span>(<span class="self">self</span>.<span class="ident">guard_count</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="macro">debug_assert_eq!</span>(<span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">get</span>(), <span class="number">0</span>);
<span class="comment">// Temporarily increment handle count. This is required so that the following call to `pin`</span>
<span class="comment">// doesn't call `finalize` again.</span>
<span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">set</span>(<span class="number">1</span>);
<span class="kw">unsafe</span> {
<span class="comment">// Pin and move the local bag into the global queue. It's important that `push_bag`</span>
<span class="comment">// doesn't defer destruction on any new garbage.</span>
<span class="kw">let</span> <span class="ident">guard</span> <span class="op">=</span> <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">pin</span>();
<span class="self">self</span>.<span class="ident">global</span>()
.<span class="ident">push_bag</span>(<span class="self">self</span>.<span class="ident">bag</span>.<span class="ident">with_mut</span>(<span class="op">|</span><span class="ident">b</span><span class="op">|</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">b</span>), <span class="ident">guard</span>);
}
<span class="comment">// Revert the handle count back to zero.</span>
<span class="self">self</span>.<span class="ident">handle_count</span>.<span class="ident">set</span>(<span class="number">0</span>);
<span class="kw">unsafe</span> {
<span class="comment">// Take the reference to the `Global` out of this `Local`. Since we're not protected</span>
<span class="comment">// by a guard at this time, it's crucial that the reference is read before marking the</span>
<span class="comment">// `Local` as deleted.</span>
<span class="kw">let</span> <span class="ident">collector</span>: <span class="ident">Collector</span> <span class="op">=</span> <span class="ident">ptr::read</span>(<span class="self">self</span>.<span class="ident">collector</span>.<span class="ident">with</span>(<span class="op">|</span><span class="ident">c</span><span class="op">|</span> <span class="kw-2">&</span><span class="kw-2">*</span>(<span class="kw-2">*</span><span class="ident">c</span>)));
<span class="comment">// Mark this node in the linked list as deleted.</span>
<span class="self">self</span>.<span class="ident">entry</span>.<span class="ident">delete</span>(<span class="ident">unprotected</span>());
<span class="comment">// Finally, drop the reference to the global. Note that this might be the last reference</span>
<span class="comment">// to the `Global`. If so, the global data will be destroyed and all deferred functions</span>
<span class="comment">// in its queue will be executed.</span>
<span class="ident">drop</span>(<span class="ident">collector</span>);
}
}
}
<span class="kw">impl</span> <span class="ident">IsElement</span><span class="op"><</span><span class="ident">Local</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Local</span> {
<span class="kw">fn</span> <span class="ident">entry_of</span>(<span class="ident">local</span>: <span class="kw-2">&</span><span class="ident">Local</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">Entry</span> {
<span class="kw">let</span> <span class="ident">entry_ptr</span> <span class="op">=</span> (<span class="ident">local</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Local</span> <span class="kw">as</span> <span class="ident">usize</span> <span class="op">+</span> <span class="macro">offset_of!</span>(<span class="ident">Local</span>, <span class="ident">entry</span>)) <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Entry</span>;
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">entry_ptr</span> }
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">element_of</span>(<span class="ident">entry</span>: <span class="kw-2">&</span><span class="ident">Entry</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">Local</span> {
<span class="comment">// offset_of! macro uses unsafe, but it's unnecessary in this context.</span>
<span class="attribute">#[<span class="ident">allow</span>(<span class="ident">unused_unsafe</span>)]</span>
<span class="kw">let</span> <span class="ident">local_ptr</span> <span class="op">=</span> (<span class="ident">entry</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Entry</span> <span class="kw">as</span> <span class="ident">usize</span> <span class="op">-</span> <span class="macro">offset_of!</span>(<span class="ident">Local</span>, <span class="ident">entry</span>)) <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Local</span>;
<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">local_ptr</span>
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">finalize</span>(<span class="ident">entry</span>: <span class="kw-2">&</span><span class="ident">Entry</span>, <span class="ident">guard</span>: <span class="kw-2">&</span><span class="ident">Guard</span>) {
<span class="ident">guard</span>.<span class="ident">defer_destroy</span>(<span class="ident">Shared::from</span>(<span class="self">Self</span><span class="ident">::element_of</span>(<span class="ident">entry</span>) <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="kw">_</span>));
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">test</span>, <span class="ident">not</span>(<span class="ident">crossbeam_loom</span>)))]</span>
<span class="kw">mod</span> <span class="ident">tests</span> {
<span class="kw">use</span> <span class="ident">std::sync::atomic</span>::{<span class="ident">AtomicUsize</span>, <span class="ident">Ordering</span>};
<span class="kw">use</span> <span class="kw">super</span>::<span class="kw-2">*</span>;
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">check_defer</span>() {
<span class="kw">static</span> <span class="ident">FLAG</span>: <span class="ident">AtomicUsize</span> <span class="op">=</span> <span class="ident">AtomicUsize::new</span>(<span class="number">0</span>);
<span class="kw">fn</span> <span class="ident">set</span>() {
<span class="ident">FLAG</span>.<span class="ident">store</span>(<span class="number">42</span>, <span class="ident">Ordering::Relaxed</span>);
}
<span class="kw">let</span> <span class="ident">d</span> <span class="op">=</span> <span class="ident">Deferred::new</span>(<span class="ident">set</span>);
<span class="macro">assert_eq!</span>(<span class="ident">FLAG</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>), <span class="number">0</span>);
<span class="ident">d</span>.<span class="ident">call</span>();
<span class="macro">assert_eq!</span>(<span class="ident">FLAG</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>), <span class="number">42</span>);
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">check_bag</span>() {
<span class="kw">static</span> <span class="ident">FLAG</span>: <span class="ident">AtomicUsize</span> <span class="op">=</span> <span class="ident">AtomicUsize::new</span>(<span class="number">0</span>);
<span class="kw">fn</span> <span class="ident">incr</span>() {
<span class="ident">FLAG</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">Ordering::Relaxed</span>);
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">bag</span> <span class="op">=</span> <span class="ident">Bag::new</span>();
<span class="macro">assert!</span>(<span class="ident">bag</span>.<span class="ident">is_empty</span>());
<span class="kw">for</span> <span class="kw">_</span> <span class="kw">in</span> <span class="number">0</span>..<span class="ident">MAX_OBJECTS</span> {
<span class="macro">assert!</span>(<span class="kw">unsafe</span> { <span class="ident">bag</span>.<span class="ident">try_push</span>(<span class="ident">Deferred::new</span>(<span class="ident">incr</span>)).<span class="ident">is_ok</span>() });
<span class="macro">assert!</span>(<span class="op">!</span><span class="ident">bag</span>.<span class="ident">is_empty</span>());
<span class="macro">assert_eq!</span>(<span class="ident">FLAG</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>), <span class="number">0</span>);
}
<span class="kw">let</span> <span class="ident">result</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">bag</span>.<span class="ident">try_push</span>(<span class="ident">Deferred::new</span>(<span class="ident">incr</span>)) };
<span class="macro">assert!</span>(<span class="ident">result</span>.<span class="ident">is_err</span>());
<span class="macro">assert!</span>(<span class="op">!</span><span class="ident">bag</span>.<span class="ident">is_empty</span>());
<span class="macro">assert_eq!</span>(<span class="ident">FLAG</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>), <span class="number">0</span>);
<span class="ident">drop</span>(<span class="ident">bag</span>);
<span class="macro">assert_eq!</span>(<span class="ident">FLAG</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>), <span class="ident">MAX_OBJECTS</span>);
}
}
</pre></div>
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