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</pre><pre class="rust ">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cmp</span>::{<span class="ident">Eq</span>, <span class="ident">PartialEq</span>, <span class="ident">PartialOrd</span>, <span class="ident">Ord</span>, <span class="ident">Ordering</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">collections</span>::<span class="ident">BinaryHeap</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>::{<span class="self">self</span>, <span class="ident">Debug</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">iter</span>::<span class="ident">FromIterator</span>;
<span class="kw">use</span> {<span class="ident">Async</span>, <span class="ident">Future</span>, <span class="ident">IntoFuture</span>, <span class="ident">Poll</span>, <span class="ident">Stream</span>};
<span class="kw">use</span> <span class="ident">stream</span>::<span class="ident">FuturesUnordered</span>;
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">item</span>: <span class="ident">T</span>,
<span class="ident">index</span>: <span class="ident">usize</span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">PartialEq</span> <span class="kw">for</span> <span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="self">Self</span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="self">self</span>.<span class="ident">index</span> <span class="op">==</span> <span class="ident">other</span>.<span class="ident">index</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Eq</span> <span class="kw">for</span> <span class="ident">OrderWrapper</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="ident">T</span><span class="op">></span> <span class="ident">PartialOrd</span> <span class="kw">for</span> <span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">partial_cmp</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="self">Self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Ordering</span><span class="op">></span> {
<span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">cmp</span>(<span class="ident">other</span>))
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Ord</span> <span class="kw">for</span> <span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">cmp</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="self">Self</span>) <span class="op">-></span> <span class="ident">Ordering</span> {
<span class="comment">// BinaryHeap is a max heap, so compare backwards here.</span>
<span class="ident">other</span>.<span class="ident">index</span>.<span class="ident">cmp</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">index</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Future</span> <span class="kw">for</span> <span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Future</span>
{
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span>::<span class="ident">Item</span><span class="op">></span>;
<span class="kw">type</span> <span class="ident">Error</span> <span class="op">=</span> <span class="ident">T</span>::<span class="ident">Error</span>;
<span class="kw">fn</span> <span class="ident">poll</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="self">Self</span>::<span class="ident">Item</span>, <span class="self">Self</span>::<span class="ident">Error</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">result</span> <span class="op">=</span> <span class="macro">try_ready</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">item</span>.<span class="ident">poll</span>());
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">OrderWrapper</span> {
<span class="ident">item</span>: <span class="ident">result</span>,
<span class="ident">index</span>: <span class="self">self</span>.<span class="ident">index</span>
}))
}
}
<span class="doccomment">/// An unbounded queue of futures.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This "combinator" is similar to `FuturesUnordered`, but it imposes an order</span>
<span class="doccomment">/// on top of the set of futures. While futures in the set will race to</span>
<span class="doccomment">/// completion in parallel, results will only be returned in the order their</span>
<span class="doccomment">/// originating futures were added to the queue.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Futures are pushed into this queue and their realized values are yielded in</span>
<span class="doccomment">/// order. This structure is optimized to manage a large number of futures.</span>
<span class="doccomment">/// Futures managed by `FuturesOrdered` will only be polled when they generate</span>
<span class="doccomment">/// notifications. This reduces the required amount of work needed to coordinate</span>
<span class="doccomment">/// large numbers of futures.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When a `FuturesOrdered` is first created, it does not contain any futures.</span>
<span class="doccomment">/// Calling `poll` in this state will result in `Ok(Async::Ready(None))` to be</span>
<span class="doccomment">/// returned. Futures are submitted to the queue using `push`; however, the</span>
<span class="doccomment">/// future will **not** be polled at this point. `FuturesOrdered` will only</span>
<span class="doccomment">/// poll managed futures when `FuturesOrdered::poll` is called. As such, it</span>
<span class="doccomment">/// is important to call `poll` after pushing new futures.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If `FuturesOrdered::poll` returns `Ok(Async::Ready(None))` this means that</span>
<span class="doccomment">/// the queue is currently not managing any futures. A future may be submitted</span>
<span class="doccomment">/// to the queue at a later time. At that point, a call to</span>
<span class="doccomment">/// `FuturesOrdered::poll` will either return the future's resolved value</span>
<span class="doccomment">/// **or** `Ok(Async::NotReady)` if the future has not yet completed. When</span>
<span class="doccomment">/// multiple futures are submitted to the queue, `FuturesOrdered::poll` will</span>
<span class="doccomment">/// return `Ok(Async::NotReady)` until the first future completes, even if</span>
<span class="doccomment">/// some of the later futures have already completed.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that you can create a ready-made `FuturesOrdered` via the</span>
<span class="doccomment">/// `futures_ordered` function in the `stream` module, or you can start with an</span>
<span class="doccomment">/// empty queue with the `FuturesOrdered::new` constructor.</span>
<span class="attribute">#[<span class="ident">must_use</span> <span class="op">=</span> <span class="string">"streams do nothing unless polled"</span>]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">FuturesOrdered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Future</span>
{
<span class="ident">in_progress</span>: <span class="ident">FuturesUnordered</span><span class="op"><</span><span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">queued_results</span>: <span class="ident">BinaryHeap</span><span class="op"><</span><span class="ident">OrderWrapper</span><span class="op"><</span><span class="ident">T</span>::<span class="ident">Item</span><span class="op">>></span>,
<span class="ident">next_incoming_index</span>: <span class="ident">usize</span>,
<span class="ident">next_outgoing_index</span>: <span class="ident">usize</span>,
}
<span class="doccomment">/// Converts a list of futures into a `Stream` of results from the futures.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function will take an list of futures (e.g. a vector, an iterator,</span>
<span class="doccomment">/// etc), and return a stream. The stream will yield items as they become</span>
<span class="doccomment">/// available on the futures internally, in the order that their originating</span>
<span class="doccomment">/// futures were submitted to the queue. If the futures complete out of order,</span>
<span class="doccomment">/// items will be stored internally within `FuturesOrdered` until all preceding</span>
<span class="doccomment">/// items have been yielded.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that the returned queue can also be used to dynamically push more</span>
<span class="doccomment">/// futures into the queue as they become available.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">futures_ordered</span><span class="op"><</span><span class="ident">I</span><span class="op">></span>(<span class="ident">futures</span>: <span class="ident">I</span>) <span class="op">-></span> <span class="ident">FuturesOrdered</span><span class="op"><<</span><span class="ident">I</span>::<span class="ident">Item</span> <span class="kw">as</span> <span class="ident">IntoFuture</span><span class="op">></span>::<span class="ident">Future</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">I</span>: <span class="ident">IntoIterator</span>,
<span class="ident">I</span>::<span class="ident">Item</span>: <span class="ident">IntoFuture</span>
{
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">queue</span> <span class="op">=</span> <span class="ident">FuturesOrdered</span>::<span class="ident">new</span>();
<span class="kw">for</span> <span class="ident">future</span> <span class="kw">in</span> <span class="ident">futures</span> {
<span class="ident">queue</span>.<span class="ident">push</span>(<span class="ident">future</span>.<span class="ident">into_future</span>());
}
<span class="kw">return</span> <span class="ident">queue</span>
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">FuturesOrdered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Future</span>
{
<span class="doccomment">/// Constructs a new, empty `FuturesOrdered`</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The returned `FuturesOrdered` does not contain any futures and, in this</span>
<span class="doccomment">/// state, `FuturesOrdered::poll` will return `Ok(Async::Ready(None))`.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">FuturesOrdered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">FuturesOrdered</span> {
<span class="ident">in_progress</span>: <span class="ident">FuturesUnordered</span>::<span class="ident">new</span>(),
<span class="ident">queued_results</span>: <span class="ident">BinaryHeap</span>::<span class="ident">new</span>(),
<span class="ident">next_incoming_index</span>: <span class="number">0</span>,
<span class="ident">next_outgoing_index</span>: <span class="number">0</span>,
}
}
<span class="doccomment">/// Returns the number of futures contained in the queue.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This represents the total number of in-flight futures, both</span>
<span class="doccomment">/// those currently processing and those that have completed but</span>
<span class="doccomment">/// which are waiting for earlier futures to complete.</span>
<span class="kw">pub</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="ident">in_progress</span>.<span class="ident">len</span>() <span class="op">+</span> <span class="self">self</span>.<span class="ident">queued_results</span>.<span class="ident">len</span>()
}
<span class="doccomment">/// Returns `true` if the queue contains no futures</span>
<span class="kw">pub</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="ident">bool</span> {
<span class="self">self</span>.<span class="ident">in_progress</span>.<span class="ident">is_empty</span>() <span class="op">&&</span> <span class="self">self</span>.<span class="ident">queued_results</span>.<span class="ident">is_empty</span>()
}
<span class="doccomment">/// Push a future into the queue.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function submits the given future to the internal set for managing.</span>
<span class="doccomment">/// This function will not call `poll` on the submitted future. The caller</span>
<span class="doccomment">/// must ensure that `FuturesOrdered::poll` is called in order to receive</span>
<span class="doccomment">/// task notifications.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">push</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">future</span>: <span class="ident">T</span>) {
<span class="kw">let</span> <span class="ident">wrapped</span> <span class="op">=</span> <span class="ident">OrderWrapper</span> {
<span class="ident">item</span>: <span class="ident">future</span>,
<span class="ident">index</span>: <span class="self">self</span>.<span class="ident">next_incoming_index</span>,
};
<span class="self">self</span>.<span class="ident">next_incoming_index</span> <span class="op">+=</span> <span class="number">1</span>;
<span class="self">self</span>.<span class="ident">in_progress</span>.<span class="ident">push</span>(<span class="ident">wrapped</span>);
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Stream</span> <span class="kw">for</span> <span class="ident">FuturesOrdered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Future</span>
{
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">T</span>::<span class="ident">Item</span>;
<span class="kw">type</span> <span class="ident">Error</span> <span class="op">=</span> <span class="ident">T</span>::<span class="ident">Error</span>;
<span class="kw">fn</span> <span class="ident">poll</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="self">Self</span>::<span class="ident">Item</span><span class="op">></span>, <span class="self">Self</span>::<span class="ident">Error</span><span class="op">></span> {
<span class="comment">// Get any completed futures from the unordered set.</span>
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">in_progress</span>.<span class="ident">poll</span>()<span class="question-mark">?</span> {
<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="prelude-val">Some</span>(<span class="ident">result</span>)) <span class="op">=></span> <span class="self">self</span>.<span class="ident">queued_results</span>.<span class="ident">push</span>(<span class="ident">result</span>),
<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="prelude-val">None</span>) <span class="op">|</span> <span class="ident">Async</span>::<span class="ident">NotReady</span> <span class="op">=></span> <span class="kw">break</span>,
}
}
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">next_result</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">queued_results</span>.<span class="ident">peek</span>() {
<span class="comment">// PeekMut::pop is not stable yet QQ</span>
<span class="kw">if</span> <span class="ident">next_result</span>.<span class="ident">index</span> <span class="op">!=</span> <span class="self">self</span>.<span class="ident">next_outgoing_index</span> {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>);
}
} <span class="kw">else</span> <span class="kw">if</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">in_progress</span>.<span class="ident">is_empty</span>() {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>);
} <span class="kw">else</span> {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="prelude-val">None</span>));
}
<span class="kw">let</span> <span class="ident">next_result</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">queued_results</span>.<span class="ident">pop</span>().<span class="ident">unwrap</span>();
<span class="self">self</span>.<span class="ident">next_outgoing_index</span> <span class="op">+=</span> <span class="number">1</span>;
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="prelude-val">Some</span>(<span class="ident">next_result</span>.<span class="ident">item</span>)))
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Debug</span><span class="op">></span> <span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">FuturesOrdered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Future</span>
{
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">fmt</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="macro">write</span><span class="macro">!</span>(<span class="ident">fmt</span>, <span class="string">"FuturesOrdered {{ ... }}"</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">F</span>: <span class="ident">Future</span><span class="op">></span> <span class="ident">FromIterator</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> <span class="kw">for</span> <span class="ident">FuturesOrdered</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from_iter</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">iter</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="self">Self</span>
<span class="kw">where</span> <span class="ident">T</span>: <span class="ident">IntoIterator</span><span class="op"><</span><span class="ident">Item</span> <span class="op">=</span> <span class="ident">F</span><span class="op">></span>
{
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">new</span> <span class="op">=</span> <span class="ident">FuturesOrdered</span>::<span class="ident">new</span>();
<span class="kw">for</span> <span class="ident">future</span> <span class="kw">in</span> <span class="ident">iter</span>.<span class="ident">into_iter</span>() {
<span class="ident">new</span>.<span class="ident">push</span>(<span class="ident">future</span>);
}
<span class="ident">new</span>
}
}
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