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</pre><pre class="rust ">
<span class="comment">// Data structures for storing garbage to be freed later (once the</span>
<span class="comment">// epochs have sufficiently advanced).</span>
<span class="comment">//</span>
<span class="comment">// In general, we try to manage the garbage thread locally whenever</span>
<span class="comment">// possible. Each thread keep track of three bags of garbage. But if a</span>
<span class="comment">// thread is exiting, these bags must be moved into the global garbage</span>
<span class="comment">// bags.</span>
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ptr</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">mem</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::<span class="ident">AtomicPtr</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::<span class="ident">Ordering</span>::{<span class="ident">Relaxed</span>, <span class="ident">Release</span>, <span class="ident">Acquire</span>};
<span class="kw">use</span> <span class="ident">mem</span>::<span class="ident">ZerosValid</span>;
<span class="doccomment">/// One item of garbage.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Stores enough information to do a deallocation.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">Item</span> {
<span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>,
<span class="ident">free</span>: <span class="kw">unsafe</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>),
}
<span class="doccomment">/// A single, thread-local bag of garbage.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Bag</span>(<span class="ident">Vec</span><span class="op"><</span><span class="ident">Item</span><span class="op">></span>);
<span class="kw">impl</span> <span class="ident">Bag</span> {
<span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Bag</span> {
<span class="ident">Bag</span>(<span class="macro">vec</span><span class="macro">!</span>[])
}
<span class="kw">fn</span> <span class="ident">insert</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">elem</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>) {
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="ident">mem</span>::<span class="ident">size_of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>();
<span class="kw">if</span> <span class="ident">size</span> <span class="op">></span> <span class="number">0</span> {
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">push</span>(<span class="ident">Item</span> {
<span class="ident">ptr</span>: <span class="ident">elem</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>,
<span class="ident">free</span>: <span class="ident">free</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>,
})
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">free</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>) {
<span class="ident">drop</span>(<span class="ident">Vec</span>::<span class="ident">from_raw_parts</span>(<span class="ident">t</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>, <span class="number">0</span>, <span class="number">1</span>));
}
}
<span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">usize</span> {
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">len</span>()
}
<span class="doccomment">/// Deallocate all garbage in the bag</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">collect</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">data</span> <span class="op">=</span> <span class="ident">mem</span>::<span class="ident">replace</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="number">0</span>, <span class="ident">Vec</span>::<span class="ident">new</span>());
<span class="kw">for</span> <span class="ident">item</span> <span class="kw">in</span> <span class="ident">data</span>.<span class="ident">iter</span>() {
(<span class="ident">item</span>.<span class="ident">free</span>)(<span class="ident">item</span>.<span class="ident">ptr</span>);
}
<span class="ident">data</span>.<span class="ident">truncate</span>(<span class="number">0</span>);
<span class="self">self</span>.<span class="number">0</span> <span class="op">=</span> <span class="ident">data</span>;
}
}
<span class="comment">// needed because the bags store raw pointers.</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">unsafe</span> <span class="kw">impl</span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">Bag</span> {}
<span class="doccomment">/// A thread-local set of garbage bags.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Local</span> {
<span class="doccomment">/// Garbage added at least one epoch behind the current local epoch</span>
<span class="kw">pub</span> <span class="ident">old</span>: <span class="ident">Bag</span>,
<span class="doccomment">/// Garbage added in the current local epoch or earlier</span>
<span class="kw">pub</span> <span class="ident">cur</span>: <span class="ident">Bag</span>,
<span class="doccomment">/// Garbage added in the current *global* epoch</span>
<span class="kw">pub</span> <span class="ident">new</span>: <span class="ident">Bag</span>,
}
<span class="kw">impl</span> <span class="ident">Local</span> {
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Local</span> {
<span class="ident">Local</span> {
<span class="ident">old</span>: <span class="ident">Bag</span>::<span class="ident">new</span>(),
<span class="ident">cur</span>: <span class="ident">Bag</span>::<span class="ident">new</span>(),
<span class="ident">new</span>: <span class="ident">Bag</span>::<span class="ident">new</span>(),
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">insert</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">elem</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>) {
<span class="self">self</span>.<span class="ident">new</span>.<span class="ident">insert</span>(<span class="ident">elem</span>)
}
<span class="doccomment">/// Collect one epoch of garbage, rotating the local garbage bags.</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">collect</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">old</span>.<span class="ident">collect</span>();
<span class="ident">mem</span>::<span class="ident">swap</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">old</span>, <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">cur</span>);
<span class="ident">mem</span>::<span class="ident">swap</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">cur</span>, <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="ident">new</span>);
<span class="ident">ret</span>
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">size</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">usize</span> {
<span class="self">self</span>.<span class="ident">old</span>.<span class="ident">len</span>() <span class="op">+</span> <span class="self">self</span>.<span class="ident">cur</span>.<span class="ident">len</span>() <span class="op">+</span> <span class="self">self</span>.<span class="ident">new</span>.<span class="ident">len</span>()
}
}
<span class="doccomment">/// A concurrent garbage bag, currently based on Treiber's stack.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The elements are themselves owned `Bag`s.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ConcBag</span> {
<span class="ident">head</span>: <span class="ident">AtomicPtr</span><span class="op"><</span><span class="ident">Node</span><span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span> <span class="ident">ZerosValid</span> <span class="kw">for</span> <span class="ident">ConcBag</span> {}
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">Node</span> {
<span class="ident">data</span>: <span class="ident">Bag</span>,
<span class="ident">next</span>: <span class="ident">AtomicPtr</span><span class="op"><</span><span class="ident">Node</span><span class="op">></span>,
}
<span class="kw">impl</span> <span class="ident">ConcBag</span> {
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">insert</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">t</span>: <span class="ident">Bag</span>){
<span class="kw">let</span> <span class="ident">n</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">Box</span>::<span class="ident">new</span>(
<span class="ident">Node</span> { <span class="ident">data</span>: <span class="ident">t</span>, <span class="ident">next</span>: <span class="ident">AtomicPtr</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>()) }));
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="ident">head</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">head</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>);
<span class="kw">unsafe</span> { (<span class="kw-2">*</span><span class="ident">n</span>).<span class="ident">next</span>.<span class="ident">store</span>(<span class="ident">head</span>, <span class="ident">Relaxed</span>) };
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">head</span>.<span class="ident">compare_and_swap</span>(<span class="ident">head</span>, <span class="ident">n</span>, <span class="ident">Release</span>) <span class="op">==</span> <span class="ident">head</span> { <span class="kw">break</span> }
}
}
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">collect</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// check to avoid xchg instruction</span>
<span class="comment">// when no garbage exists</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">head</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">head</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
<span class="kw">if</span> <span class="ident">head</span> <span class="op">!=</span> <span class="ident">ptr</span>::<span class="ident">null_mut</span>() {
<span class="ident">head</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">head</span>.<span class="ident">swap</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>(), <span class="ident">Acquire</span>);
<span class="kw">while</span> <span class="ident">head</span> <span class="op">!=</span> <span class="ident">ptr</span>::<span class="ident">null_mut</span>() {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">n</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">head</span>);
<span class="ident">n</span>.<span class="ident">data</span>.<span class="ident">collect</span>();
<span class="ident">head</span> <span class="op">=</span> <span class="ident">n</span>.<span class="ident">next</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>);
}
}
}
}
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