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</pre><pre class="rust">
<span class="kw">use</span> <span class="kw">super</span><span class="ident">::plumbing</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="kw">super</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">std::cell::Cell</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="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">test</span>;
<span class="comment">// The key optimization for find_first is that a consumer can stop its search if</span>
<span class="comment">// some consumer to its left already found a match (and similarly for consumers</span>
<span class="comment">// to the right for find_last). To make this work, all consumers need some</span>
<span class="comment">// notion of their position in the data relative to other consumers, including</span>
<span class="comment">// unindexed consumers that have no built-in notion of position.</span>
<span class="comment">//</span>
<span class="comment">// To solve this, we assign each consumer a lower and upper bound for an</span>
<span class="comment">// imaginary "range" of data that it consumes. The initial consumer starts with</span>
<span class="comment">// the range 0..usize::max_value(). The split divides this range in half so that</span>
<span class="comment">// one resulting consumer has the range 0..(usize::max_value() / 2), and the</span>
<span class="comment">// other has (usize::max_value() / 2)..usize::max_value(). Every subsequent</span>
<span class="comment">// split divides the range in half again until it cannot be split anymore</span>
<span class="comment">// (i.e. its length is 1), in which case the split returns two consumers with</span>
<span class="comment">// the same range. In that case both consumers will continue to consume all</span>
<span class="comment">// their data regardless of whether a better match is found, but the reducer</span>
<span class="comment">// will still return the correct answer.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>)]</span>
<span class="kw">enum</span> <span class="ident">MatchPosition</span> {
<span class="ident">Leftmost</span>,
<span class="ident">Rightmost</span>,
}
<span class="doccomment">/// Returns true if pos1 is a better match than pos2 according to MatchPosition</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">better_position</span>(<span class="ident">pos1</span>: <span class="ident">usize</span>, <span class="ident">pos2</span>: <span class="ident">usize</span>, <span class="ident">mp</span>: <span class="ident">MatchPosition</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="kw">match</span> <span class="ident">mp</span> {
<span class="ident">MatchPosition::Leftmost</span> <span class="op">=</span><span class="op">></span> <span class="ident">pos1</span> <span class="op"><</span> <span class="ident">pos2</span>,
<span class="ident">MatchPosition::Rightmost</span> <span class="op">=</span><span class="op">></span> <span class="ident">pos1</span> <span class="op">></span> <span class="ident">pos2</span>,
}
}
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn</span> <span class="ident">find_first</span><span class="op"><</span><span class="ident">I</span>, <span class="ident">P</span><span class="op">></span>(<span class="ident">pi</span>: <span class="ident">I</span>, <span class="ident">find_op</span>: <span class="ident">P</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">I::Item</span><span class="op">></span>
<span class="kw">where</span>
<span class="ident">I</span>: <span class="ident">ParallelIterator</span>,
<span class="ident">P</span>: <span class="ident">Fn</span>(<span class="kw-2">&</span><span class="ident">I::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> <span class="op">+</span> <span class="ident">Sync</span>,
{
<span class="kw">let</span> <span class="ident">best_found</span> <span class="op">=</span> <span class="ident">AtomicUsize::new</span>(<span class="ident">usize::max_value</span>());
<span class="kw">let</span> <span class="ident">consumer</span> <span class="op">=</span> <span class="ident">FindConsumer::new</span>(<span class="kw-2">&</span><span class="ident">find_op</span>, <span class="ident">MatchPosition::Leftmost</span>, <span class="kw-2">&</span><span class="ident">best_found</span>);
<span class="ident">pi</span>.<span class="ident">drive_unindexed</span>(<span class="ident">consumer</span>)
}
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn</span> <span class="ident">find_last</span><span class="op"><</span><span class="ident">I</span>, <span class="ident">P</span><span class="op">></span>(<span class="ident">pi</span>: <span class="ident">I</span>, <span class="ident">find_op</span>: <span class="ident">P</span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">I::Item</span><span class="op">></span>
<span class="kw">where</span>
<span class="ident">I</span>: <span class="ident">ParallelIterator</span>,
<span class="ident">P</span>: <span class="ident">Fn</span>(<span class="kw-2">&</span><span class="ident">I::Item</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> <span class="op">+</span> <span class="ident">Sync</span>,
{
<span class="kw">let</span> <span class="ident">best_found</span> <span class="op">=</span> <span class="ident">AtomicUsize::new</span>(<span class="number">0</span>);
<span class="kw">let</span> <span class="ident">consumer</span> <span class="op">=</span> <span class="ident">FindConsumer::new</span>(<span class="kw-2">&</span><span class="ident">find_op</span>, <span class="ident">MatchPosition::Rightmost</span>, <span class="kw-2">&</span><span class="ident">best_found</span>);
<span class="ident">pi</span>.<span class="ident">drive_unindexed</span>(<span class="ident">consumer</span>)
}
<span class="kw">struct</span> <span class="ident">FindConsumer</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">P</span><span class="op">></span> {
<span class="ident">find_op</span>: <span class="kw-2">&</span><span class="lifetime">'p</span> <span class="ident">P</span>,
<span class="ident">lower_bound</span>: <span class="ident">Cell</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>,
<span class="ident">upper_bound</span>: <span class="ident">usize</span>,
<span class="ident">match_position</span>: <span class="ident">MatchPosition</span>,
<span class="ident">best_found</span>: <span class="kw-2">&</span><span class="lifetime">'p</span> <span class="ident">AtomicUsize</span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">P</span><span class="op">></span> <span class="ident">FindConsumer</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">P</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">find_op</span>: <span class="kw-2">&</span><span class="lifetime">'p</span> <span class="ident">P</span>, <span class="ident">match_position</span>: <span class="ident">MatchPosition</span>, <span class="ident">best_found</span>: <span class="kw-2">&</span><span class="lifetime">'p</span> <span class="ident">AtomicUsize</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="ident">FindConsumer</span> {
<span class="ident">find_op</span>,
<span class="ident">lower_bound</span>: <span class="ident">Cell::new</span>(<span class="number">0</span>),
<span class="ident">upper_bound</span>: <span class="ident">usize::max_value</span>(),
<span class="ident">match_position</span>,
<span class="ident">best_found</span>,
}
}
<span class="kw">fn</span> <span class="ident">current_index</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">usize</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">match_position</span> {
<span class="ident">MatchPosition::Leftmost</span> <span class="op">=</span><span class="op">></span> <span class="self">self</span>.<span class="ident">lower_bound</span>.<span class="ident">get</span>(),
<span class="ident">MatchPosition::Rightmost</span> <span class="op">=</span><span class="op">></span> <span class="self">self</span>.<span class="ident">upper_bound</span>,
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">T</span>, <span class="ident">P</span><span class="op">></span> <span class="ident">Consumer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">FindConsumer</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">P</span><span class="op">></span>
<span class="kw">where</span>
<span class="ident">T</span>: <span class="ident">Send</span>,
<span class="ident">P</span>: <span class="ident">Fn</span>(<span class="kw-2">&</span><span class="ident">T</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> <span class="op">+</span> <span class="ident">Sync</span>,
{
<span class="kw">type</span> <span class="ident">Folder</span> <span class="op">=</span> <span class="ident">FindFolder</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">T</span>, <span class="ident">P</span><span class="op">></span>;
<span class="kw">type</span> <span class="ident">Reducer</span> <span class="op">=</span> <span class="ident">FindReducer</span>;
<span class="kw">type</span> <span class="prelude-ty">Result</span> <span class="op">=</span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>;
<span class="kw">fn</span> <span class="ident">split_at</span>(<span class="self">self</span>, <span class="ident">_index</span>: <span class="ident">usize</span>) <span class="op">-</span><span class="op">></span> (<span class="self">Self</span>, <span class="self">Self</span>, <span class="self">Self</span><span class="ident">::Reducer</span>) {
<span class="kw">let</span> <span class="ident">dir</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">match_position</span>;
(
<span class="self">self</span>.<span class="ident">split_off_left</span>(),
<span class="self">self</span>,
<span class="ident">FindReducer</span> {
<span class="ident">match_position</span>: <span class="ident">dir</span>,
},
)
}
<span class="kw">fn</span> <span class="ident">into_folder</span>(<span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span><span class="ident">::Folder</span> {
<span class="ident">FindFolder</span> {
<span class="ident">find_op</span>: <span class="self">self</span>.<span class="ident">find_op</span>,
<span class="ident">boundary</span>: <span class="self">self</span>.<span class="ident">current_index</span>(),
<span class="ident">match_position</span>: <span class="self">self</span>.<span class="ident">match_position</span>,
<span class="ident">best_found</span>: <span class="self">self</span>.<span class="ident">best_found</span>,
<span class="ident">item</span>: <span class="prelude-val">None</span>,
}
}
<span class="kw">fn</span> <span class="ident">full</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="comment">// can stop consuming if the best found index so far is *strictly*</span>
<span class="comment">// better than anything this consumer will find</span>
<span class="ident">better_position</span>(
<span class="self">self</span>.<span class="ident">best_found</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>),
<span class="self">self</span>.<span class="ident">current_index</span>(),
<span class="self">self</span>.<span class="ident">match_position</span>,
)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">T</span>, <span class="ident">P</span><span class="op">></span> <span class="ident">UnindexedConsumer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">FindConsumer</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">P</span><span class="op">></span>
<span class="kw">where</span>
<span class="ident">T</span>: <span class="ident">Send</span>,
<span class="ident">P</span>: <span class="ident">Fn</span>(<span class="kw-2">&</span><span class="ident">T</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> <span class="op">+</span> <span class="ident">Sync</span>,
{
<span class="kw">fn</span> <span class="ident">split_off_left</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="comment">// Upper bound for one consumer will be lower bound for the other. This</span>
<span class="comment">// overlap is okay, because only one of the bounds will be used for</span>
<span class="comment">// comparing against best_found; the other is kept only to be able to</span>
<span class="comment">// divide the range in half.</span>
<span class="comment">//</span>
<span class="comment">// When the resolution of usize has been exhausted (i.e. when</span>
<span class="comment">// upper_bound = lower_bound), both results of this split will have the</span>
<span class="comment">// same range. When that happens, we lose the ability to tell one</span>
<span class="comment">// consumer to stop working when the other finds a better match, but the</span>
<span class="comment">// reducer ensures that the best answer is still returned (see the test</span>
<span class="comment">// above).</span>
<span class="kw">let</span> <span class="ident">old_lower_bound</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">lower_bound</span>.<span class="ident">get</span>();
<span class="kw">let</span> <span class="ident">median</span> <span class="op">=</span> <span class="ident">old_lower_bound</span> <span class="op">+</span> ((<span class="self">self</span>.<span class="ident">upper_bound</span> <span class="op">-</span> <span class="ident">old_lower_bound</span>) <span class="op">/</span> <span class="number">2</span>);
<span class="self">self</span>.<span class="ident">lower_bound</span>.<span class="ident">set</span>(<span class="ident">median</span>);
<span class="ident">FindConsumer</span> {
<span class="ident">find_op</span>: <span class="self">self</span>.<span class="ident">find_op</span>,
<span class="ident">lower_bound</span>: <span class="ident">Cell::new</span>(<span class="ident">old_lower_bound</span>),
<span class="ident">upper_bound</span>: <span class="ident">median</span>,
<span class="ident">match_position</span>: <span class="self">self</span>.<span class="ident">match_position</span>,
<span class="ident">best_found</span>: <span class="self">self</span>.<span class="ident">best_found</span>,
}
}
<span class="kw">fn</span> <span class="ident">to_reducer</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span><span class="ident">::Reducer</span> {
<span class="ident">FindReducer</span> {
<span class="ident">match_position</span>: <span class="self">self</span>.<span class="ident">match_position</span>,
}
}
}
<span class="kw">struct</span> <span class="ident">FindFolder</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">T</span>, <span class="ident">P</span><span class="op">></span> {
<span class="ident">find_op</span>: <span class="kw-2">&</span><span class="lifetime">'p</span> <span class="ident">P</span>,
<span class="ident">boundary</span>: <span class="ident">usize</span>,
<span class="ident">match_position</span>: <span class="ident">MatchPosition</span>,
<span class="ident">best_found</span>: <span class="kw-2">&</span><span class="lifetime">'p</span> <span class="ident">AtomicUsize</span>,
<span class="ident">item</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">P</span>: <span class="lifetime">'p</span> <span class="op">+</span> <span class="ident">Fn</span>(<span class="kw-2">&</span><span class="ident">T</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Folder</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">FindFolder</span><span class="op"><</span><span class="lifetime">'p</span>, <span class="ident">T</span>, <span class="ident">P</span><span class="op">></span> {
<span class="kw">type</span> <span class="prelude-ty">Result</span> <span class="op">=</span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>;
<span class="kw">fn</span> <span class="ident">consume</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">item</span>: <span class="ident">T</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="kw">let</span> <span class="ident">found_best_in_range</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">match_position</span> {
<span class="ident">MatchPosition::Leftmost</span> <span class="op">=</span><span class="op">></span> <span class="self">self</span>.<span class="ident">item</span>.<span class="ident">is_some</span>(),
<span class="ident">MatchPosition::Rightmost</span> <span class="op">=</span><span class="op">></span> <span class="bool-val">false</span>,
};
<span class="kw">if</span> <span class="op">!</span><span class="ident">found_best_in_range</span> <span class="op">&&</span> (<span class="self">self</span>.<span class="ident">find_op</span>)(<span class="kw-2">&</span><span class="ident">item</span>) {
<span class="comment">// Continuously try to set best_found until we succeed or we</span>
<span class="comment">// discover a better match was already found.</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">current</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">best_found</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>);
<span class="kw">loop</span> {
<span class="kw">if</span> <span class="ident">better_position</span>(<span class="ident">current</span>, <span class="self">self</span>.<span class="ident">boundary</span>, <span class="self">self</span>.<span class="ident">match_position</span>) {
<span class="kw">break</span>;
}
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">best_found</span>.<span class="ident">compare_exchange_weak</span>(
<span class="ident">current</span>,
<span class="self">self</span>.<span class="ident">boundary</span>,
<span class="ident">Ordering::Relaxed</span>,
<span class="ident">Ordering::Relaxed</span>,
) {
<span class="prelude-val">Ok</span>(<span class="kw">_</span>) <span class="op">=</span><span class="op">></span> {
<span class="self">self</span>.<span class="ident">item</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">item</span>);
<span class="kw">break</span>;
}
<span class="prelude-val">Err</span>(<span class="ident">v</span>) <span class="op">=</span><span class="op">></span> <span class="ident">current</span> <span class="op">=</span> <span class="ident">v</span>,
}
}
}
<span class="self">self</span>
}
<span class="kw">fn</span> <span class="ident">complete</span>(<span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span><span class="ident">::Result</span> {
<span class="self">self</span>.<span class="ident">item</span>
}
<span class="kw">fn</span> <span class="ident">full</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="kw">let</span> <span class="ident">found_best_in_range</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">match_position</span> {
<span class="ident">MatchPosition::Leftmost</span> <span class="op">=</span><span class="op">></span> <span class="self">self</span>.<span class="ident">item</span>.<span class="ident">is_some</span>(),
<span class="ident">MatchPosition::Rightmost</span> <span class="op">=</span><span class="op">></span> <span class="bool-val">false</span>,
};
<span class="ident">found_best_in_range</span>
<span class="op">|</span><span class="op">|</span> <span class="ident">better_position</span>(
<span class="self">self</span>.<span class="ident">best_found</span>.<span class="ident">load</span>(<span class="ident">Ordering::Relaxed</span>),
<span class="self">self</span>.<span class="ident">boundary</span>,
<span class="self">self</span>.<span class="ident">match_position</span>,
)
}
}
<span class="kw">struct</span> <span class="ident">FindReducer</span> {
<span class="ident">match_position</span>: <span class="ident">MatchPosition</span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Reducer</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span><span class="op">></span> <span class="kw">for</span> <span class="ident">FindReducer</span> {
<span class="kw">fn</span> <span class="ident">reduce</span>(<span class="self">self</span>, <span class="ident">left</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">right</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">match_position</span> {
<span class="ident">MatchPosition::Leftmost</span> <span class="op">=</span><span class="op">></span> <span class="ident">left</span>.<span class="ident">or</span>(<span class="ident">right</span>),
<span class="ident">MatchPosition::Rightmost</span> <span class="op">=</span><span class="op">></span> <span class="ident">right</span>.<span class="ident">or</span>(<span class="ident">left</span>),
}
}
}
</pre></div>
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