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</pre><pre class="rust ">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">UnsafeCell</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">marker</span>::<span class="ident">PhantomData</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">ptr</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">SeqCst</span>, <span class="ident">Acquire</span>, <span class="ident">Release</span>, <span class="ident">AcqRel</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="ident">AtomicBool</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::{<span class="ident">Arc</span>, <span class="ident">Weak</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">usize</span>;
<span class="kw">use</span> {<span class="ident">task</span>, <span class="ident">Stream</span>, <span class="ident">Future</span>, <span class="ident">Poll</span>, <span class="ident">Async</span>, <span class="ident">IntoFuture</span>};
<span class="kw">use</span> <span class="ident">executor</span>::{<span class="ident">Notify</span>, <span class="ident">UnsafeNotify</span>, <span class="ident">NotifyHandle</span>};
<span class="kw">use</span> <span class="ident">task_impl</span>::{<span class="self">self</span>, <span class="ident">AtomicTask</span>};
<span class="doccomment">/// An unbounded queue of futures.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This "combinator" also serves a special function in this library, providing</span>
<span class="doccomment">/// the ability to maintain a queue of futures that and manage driving them all</span>
<span class="doccomment">/// to completion.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Futures are pushed into this queue and their realized values are yielded as</span>
<span class="doccomment">/// they are ready. This structure is optimized to manage a large number of</span>
<span class="doccomment">/// futures. Futures managed by `FuturesUnordered` will only be polled when they</span>
<span class="doccomment">/// generate notifications. This reduces the required amount of work needed to</span>
<span class="doccomment">/// coordinate large numbers of futures.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When a `FuturesUnordered` 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. `FuturesUnordered` will only</span>
<span class="doccomment">/// poll managged futures when `FuturesUnordered::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 `FuturesUnordered::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">/// `FuturesUnordered::poll` will either return the future's resolved value</span>
<span class="doccomment">/// **or** `Ok(Async::NotReady)` if the future has not yet completed.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that you can create a ready-made `FuturesUnordered` via the</span>
<span class="doccomment">/// `futures_unordered` function in the `stream` module, or you can start with a</span>
<span class="doccomment">/// blank queue with the `FuturesUnordered::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">FuturesUnordered</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> {
<span class="ident">inner</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Inner</span><span class="op"><</span><span class="ident">F</span><span class="op">>></span>,
<span class="ident">len</span>: <span class="ident">usize</span>,
<span class="ident">head_all</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Send</span><span class="op">></span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">FuturesUnordered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Sync</span><span class="op">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">FuturesUnordered</span><span class="op"><</span><span class="ident">T</span><span class="op">></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 they become</span>
<span class="doccomment">/// available. This function is similar to `buffer_unordered` in that it may</span>
<span class="doccomment">/// return items in a different order than in the list specified.</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 onto the queue as they become available.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">futures_unordered</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">FuturesUnordered</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">FuturesUnordered</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="comment">// FuturesUnordered is implemented using two linked lists. One which links all</span>
<span class="comment">// futures managed by a `FuturesUnordered` and one that tracks futures that have</span>
<span class="comment">// been scheduled for polling. The first linked list is not thread safe and is</span>
<span class="comment">// only accessed by the thread that owns the `FuturesUnordered` value. The</span>
<span class="comment">// second linked list is an implementation of the intrusive MPSC queue algorithm</span>
<span class="comment">// described by 1024cores.net.</span>
<span class="comment">//</span>
<span class="comment">// When a future is submitted to the queue a node is allocated and inserted in</span>
<span class="comment">// both linked lists. The next call to `poll` will (eventually) see this node</span>
<span class="comment">// and call `poll` on the future.</span>
<span class="comment">//</span>
<span class="comment">// Before a managed future is polled, the current task's `Notify` is replaced</span>
<span class="comment">// with one that is aware of the specific future being run. This ensures that</span>
<span class="comment">// task notifications generated by that specific future are visible to</span>
<span class="comment">// `FuturesUnordered`. When a notification is received, the node is scheduled</span>
<span class="comment">// for polling by being inserted into the concurrent linked list.</span>
<span class="comment">//</span>
<span class="comment">// Each node uses an `AtomicUisze` to track it's state. The node state is the</span>
<span class="comment">// reference count (the number of outstanding handles to the node) as well as a</span>
<span class="comment">// flag tracking if the node is currently inserted in the atomic queue. When the</span>
<span class="comment">// future is notified, it will only insert itself into the linked list if it</span>
<span class="comment">// isn't currently inserted.</span>
<span class="attribute">#[<span class="ident">allow</span>(<span class="ident">missing_debug_implementations</span>)]</span>
<span class="kw">struct</span> <span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="comment">// The task using `FuturesUnordered`.</span>
<span class="ident">parent</span>: <span class="ident">AtomicTask</span>,
<span class="comment">// Head/tail of the readiness queue</span>
<span class="ident">head_readiness</span>: <span class="ident">AtomicPtr</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">tail_readiness</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="ident">stub</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
}
<span class="kw">struct</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="comment">// The future</span>
<span class="ident">future</span>: <span class="ident">UnsafeCell</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="comment">// Next pointer for linked list tracking all active nodes</span>
<span class="ident">next_all</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="comment">// Previous node in linked list tracking all active nodes</span>
<span class="ident">prev_all</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="comment">// Next pointer in readiness queue</span>
<span class="ident">next_readiness</span>: <span class="ident">AtomicPtr</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="comment">// Queue that we'll be enqueued to when notified</span>
<span class="ident">queue</span>: <span class="ident">Weak</span><span class="op"><</span><span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
<span class="comment">// Whether or not this node is currently in the mpsc queue.</span>
<span class="ident">queued</span>: <span class="ident">AtomicBool</span>,
}
<span class="kw">enum</span> <span class="ident">Dequeue</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Data</span>(<span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>),
<span class="ident">Empty</span>,
<span class="ident">Inconsistent</span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">FuturesUnordered</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 `FuturesUnordered`</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The returned `FuturesUnordered` does not contain any futures and, in this</span>
<span class="doccomment">/// state, `FuturesUnordered::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">FuturesUnordered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">stub</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Node</span> {
<span class="ident">future</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>),
<span class="ident">next_all</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null</span>()),
<span class="ident">prev_all</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null</span>()),
<span class="ident">next_readiness</span>: <span class="ident">AtomicPtr</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>()),
<span class="ident">queued</span>: <span class="ident">AtomicBool</span>::<span class="ident">new</span>(<span class="bool-val">true</span>),
<span class="ident">queue</span>: <span class="ident">Weak</span>::<span class="ident">new</span>(),
});
<span class="kw">let</span> <span class="ident">stub_ptr</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">stub</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>;
<span class="kw">let</span> <span class="ident">inner</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Inner</span> {
<span class="ident">parent</span>: <span class="ident">AtomicTask</span>::<span class="ident">new</span>(),
<span class="ident">head_readiness</span>: <span class="ident">AtomicPtr</span>::<span class="ident">new</span>(<span class="ident">stub_ptr</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> _),
<span class="ident">tail_readiness</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">stub_ptr</span>),
<span class="ident">stub</span>: <span class="ident">stub</span>,
});
<span class="ident">FuturesUnordered</span> {
<span class="ident">len</span>: <span class="number">0</span>,
<span class="ident">head_all</span>: <span class="ident">ptr</span>::<span class="ident">null_mut</span>(),
<span class="ident">inner</span>: <span class="ident">inner</span>,
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">FuturesUnordered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Returns the number of futures contained by the queue.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This represents the total number of in-flight futures.</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">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">len</span> <span class="op">==</span> <span class="number">0</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 queue for managing. This</span>
<span class="doccomment">/// function will not call `poll` on the submitted future. The caller must</span>
<span class="doccomment">/// ensure that `FuturesUnordered::poll` is called in order to receive task</span>
<span class="doccomment">/// 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">node</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Node</span> {
<span class="ident">future</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="prelude-val">Some</span>(<span class="ident">future</span>)),
<span class="ident">next_all</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>()),
<span class="ident">prev_all</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>()),
<span class="ident">next_readiness</span>: <span class="ident">AtomicPtr</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>()),
<span class="ident">queued</span>: <span class="ident">AtomicBool</span>::<span class="ident">new</span>(<span class="bool-val">true</span>),
<span class="ident">queue</span>: <span class="ident">Arc</span>::<span class="ident">downgrade</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">inner</span>),
});
<span class="comment">// Right now our node has a strong reference count of 1. We transfer</span>
<span class="comment">// ownership of this reference count to our internal linked list</span>
<span class="comment">// and we'll reclaim ownership through the `unlink` function below.</span>
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">link</span>(<span class="ident">node</span>);
<span class="comment">// We'll need to get the future "into the system" to start tracking it,</span>
<span class="comment">// e.g. getting its unpark notifications going to us tracking which</span>
<span class="comment">// futures are ready. To do that we unconditionally enqueue it for</span>
<span class="comment">// polling here.</span>
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">enqueue</span>(<span class="ident">ptr</span>);
}
<span class="kw">fn</span> <span class="ident">release_node</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">node</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>) {
<span class="comment">// The future is done, try to reset the queued flag. This will prevent</span>
<span class="comment">// `notify` from doing any work in the future</span>
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="ident">node</span>.<span class="ident">queued</span>.<span class="ident">swap</span>(<span class="bool-val">true</span>, <span class="ident">SeqCst</span>);
<span class="comment">// Drop the future, even if it hasn't finished yet. This is safe</span>
<span class="comment">// because we're dropping the future on the thread that owns</span>
<span class="comment">// `FuturesUnordered`, which correctly tracks T's lifetimes and such.</span>
<span class="kw">unsafe</span> {
<span class="ident">drop</span>((<span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">future</span>.<span class="ident">get</span>()).<span class="ident">take</span>());
}
<span class="comment">// If the queued flag was previously set then it means that this node</span>
<span class="comment">// is still in our internal mpsc queue. We then transfer ownership</span>
<span class="comment">// of our reference count to the mpsc queue, and it'll come along and</span>
<span class="comment">// free it later, noticing that the future is `None`.</span>
<span class="comment">//</span>
<span class="comment">// If, however, the queued flag was *not* set then we're safe to</span>
<span class="comment">// release our reference count on the internal node. The queued flag</span>
<span class="comment">// was set above so all future `enqueue` operations will not actually</span>
<span class="comment">// enqueue the node, so our node will never see the mpsc queue again.</span>
<span class="comment">// The node itself will be deallocated once all reference counts have</span>
<span class="comment">// been dropped by the various owning tasks elsewhere.</span>
<span class="kw">if</span> <span class="ident">prev</span> {
<span class="ident">mem</span>::<span class="ident">forget</span>(<span class="ident">node</span>);
}
}
<span class="doccomment">/// Insert a new node into the internal linked list.</span>
<span class="kw">fn</span> <span class="ident">link</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">node</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">arc2ptr</span>(<span class="ident">node</span>);
<span class="kw">unsafe</span> {
<span class="kw-2">*</span>(<span class="kw-2">*</span><span class="ident">ptr</span>).<span class="ident">next_all</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="self">self</span>.<span class="ident">head_all</span>;
<span class="kw">if</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">head_all</span>.<span class="ident">is_null</span>() {
<span class="kw-2">*</span>(<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">head_all</span>).<span class="ident">prev_all</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">ptr</span>;
}
}
<span class="self">self</span>.<span class="ident">head_all</span> <span class="op">=</span> <span class="ident">ptr</span>;
<span class="self">self</span>.<span class="ident">len</span> <span class="op">+=</span> <span class="number">1</span>;
<span class="kw">return</span> <span class="ident">ptr</span>
}
<span class="doccomment">/// Remove the node from the linked list tracking all nodes currently</span>
<span class="doccomment">/// managed by `FuturesUnordered`.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">unlink</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">node</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="kw">let</span> <span class="ident">node</span> <span class="op">=</span> <span class="ident">ptr2arc</span>(<span class="ident">node</span>);
<span class="kw">let</span> <span class="ident">next</span> <span class="op">=</span> <span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">next_all</span>.<span class="ident">get</span>();
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">prev_all</span>.<span class="ident">get</span>();
<span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">next_all</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">null_mut</span>();
<span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">prev_all</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">ptr</span>::<span class="ident">null_mut</span>();
<span class="kw">if</span> <span class="op">!</span><span class="ident">next</span>.<span class="ident">is_null</span>() {
<span class="kw-2">*</span>(<span class="kw-2">*</span><span class="ident">next</span>).<span class="ident">prev_all</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">prev</span>;
}
<span class="kw">if</span> <span class="op">!</span><span class="ident">prev</span>.<span class="ident">is_null</span>() {
<span class="kw-2">*</span>(<span class="kw-2">*</span><span class="ident">prev</span>).<span class="ident">next_all</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">next</span>;
} <span class="kw">else</span> {
<span class="self">self</span>.<span class="ident">head_all</span> <span class="op">=</span> <span class="ident">next</span>;
}
<span class="self">self</span>.<span class="ident">len</span> <span class="op">-=</span> <span class="number">1</span>;
<span class="kw">return</span> <span class="ident">node</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">FuturesUnordered</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="ident">T</span>::<span class="ident">Item</span><span class="op">></span>, <span class="ident">T</span>::<span class="ident">Error</span><span class="op">></span> {
<span class="comment">// Ensure `parent` is correctly set. Note that the `unsafe` here is</span>
<span class="comment">// because the `park` method underneath needs mutual exclusion from</span>
<span class="comment">// other calls to `park`, which we guarantee with `&mut self` above and</span>
<span class="comment">// this is the only method which calls park.</span>
<span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">parent</span>.<span class="ident">park</span>() };
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="ident">node</span> <span class="op">=</span> <span class="kw">match</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">dequeue</span>() } {
<span class="ident">Dequeue</span>::<span class="ident">Empty</span> <span class="op">=></span> {
<span class="kw">if</span> <span class="self">self</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">Ready</span>(<span class="prelude-val">None</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">NotReady</span>)
}
}
<span class="ident">Dequeue</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> {
<span class="comment">// At this point, it may be worth yielding the thread &</span>
<span class="comment">// spinning a few times... but for now, just yield using the</span>
<span class="comment">// task system.</span>
<span class="ident">task</span>::<span class="ident">current</span>().<span class="ident">notify</span>();
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>);
}
<span class="ident">Dequeue</span>::<span class="ident">Data</span>(<span class="ident">node</span>) <span class="op">=></span> <span class="ident">node</span>,
};
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">node</span> <span class="op">!=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">stub</span>());
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">future</span> <span class="op">=</span> <span class="kw">match</span> (<span class="kw-2">*</span>(<span class="kw-2">*</span><span class="ident">node</span>).<span class="ident">future</span>.<span class="ident">get</span>()).<span class="ident">take</span>() {
<span class="prelude-val">Some</span>(<span class="ident">future</span>) <span class="op">=></span> <span class="ident">future</span>,
<span class="comment">// If the future has already gone away then we're just</span>
<span class="comment">// cleaning out this node. See the comment in</span>
<span class="comment">// `release_node` for more information, but we're basically</span>
<span class="comment">// just taking ownership of our reference count here.</span>
<span class="prelude-val">None</span> <span class="op">=></span> {
<span class="kw">let</span> <span class="ident">node</span> <span class="op">=</span> <span class="ident">ptr2arc</span>(<span class="ident">node</span>);
<span class="macro">assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">next_all</span>.<span class="ident">get</span>()).<span class="ident">is_null</span>());
<span class="macro">assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">prev_all</span>.<span class="ident">get</span>()).<span class="ident">is_null</span>());
<span class="kw">continue</span>
}
};
<span class="comment">// Unset queued flag... this must be done before</span>
<span class="comment">// polling. This ensures that the future gets</span>
<span class="comment">// rescheduled if it is notified **during** a call</span>
<span class="comment">// to `poll`.</span>
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">node</span>).<span class="ident">queued</span>.<span class="ident">swap</span>(<span class="bool-val">false</span>, <span class="ident">SeqCst</span>);
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">prev</span>);
<span class="comment">// We're going to need to be very careful if the `poll`</span>
<span class="comment">// function below panics. We need to (a) not leak memory and</span>
<span class="comment">// (b) ensure that we still don't have any use-after-frees. To</span>
<span class="comment">// manage this we do a few things:</span>
<span class="comment">//</span>
<span class="comment">// * This "bomb" here will call `release_node` if dropped</span>
<span class="comment">// abnormally. That way we'll be sure the memory management</span>
<span class="comment">// of the `node` is managed correctly.</span>
<span class="comment">// * The future was extracted above (taken ownership). That way</span>
<span class="comment">// if it panics we're guaranteed that the future is</span>
<span class="comment">// dropped on this thread and doesn't accidentally get</span>
<span class="comment">// dropped on a different thread (bad).</span>
<span class="comment">// * We unlink the node from our internal queue to preemptively</span>
<span class="comment">// assume it'll panic, in which case we'll want to discard it</span>
<span class="comment">// regardless.</span>
<span class="kw">struct</span> <span class="ident">Bomb</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">queue</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="kw-2">mut</span> <span class="ident">FuturesUnordered</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">node</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Bomb</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></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="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">node</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">node</span>.<span class="ident">take</span>() {
<span class="self">self</span>.<span class="ident">queue</span>.<span class="ident">release_node</span>(<span class="ident">node</span>);
}
}
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">bomb</span> <span class="op">=</span> <span class="ident">Bomb</span> {
<span class="ident">node</span>: <span class="prelude-val">Some</span>(<span class="self">self</span>.<span class="ident">unlink</span>(<span class="ident">node</span>)),
<span class="ident">queue</span>: <span class="self">self</span>,
};
<span class="comment">// Poll the underlying future with the appropriate `notify`</span>
<span class="comment">// implementation. This is where a large bit of the unsafety</span>
<span class="comment">// starts to stem from internally. The `notify` instance itself</span>
<span class="comment">// is basically just our `Arc<Node<T>>` and tracks the mpsc</span>
<span class="comment">// queue of ready futures.</span>
<span class="comment">//</span>
<span class="comment">// Critically though `Node<T>` won't actually access `T`, the</span>
<span class="comment">// future, while it's floating around inside of `Task`</span>
<span class="comment">// instances. These structs will basically just use `T` to size</span>
<span class="comment">// the internal allocation, appropriately accessing fields and</span>
<span class="comment">// deallocating the node if need be.</span>
<span class="kw">let</span> <span class="ident">res</span> <span class="op">=</span> {
<span class="kw">let</span> <span class="ident">notify</span> <span class="op">=</span> <span class="ident">NodeToHandle</span>(<span class="ident">bomb</span>.<span class="ident">node</span>.<span class="ident">as_ref</span>().<span class="ident">unwrap</span>());
<span class="ident">task_impl</span>::<span class="ident">with_notify</span>(<span class="kw-2">&</span><span class="ident">notify</span>, <span class="number">0</span>, <span class="op">||</span> {
<span class="ident">future</span>.<span class="ident">poll</span>()
})
};
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">res</span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>) <span class="op">=></span> {
<span class="kw">let</span> <span class="ident">node</span> <span class="op">=</span> <span class="ident">bomb</span>.<span class="ident">node</span>.<span class="ident">take</span>().<span class="ident">unwrap</span>();
<span class="kw-2">*</span><span class="ident">node</span>.<span class="ident">future</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">future</span>);
<span class="ident">bomb</span>.<span class="ident">queue</span>.<span class="ident">link</span>(<span class="ident">node</span>);
<span class="kw">continue</span>
}
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">e</span>)) <span class="op">=></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">e</span>))),
<span class="prelude-val">Err</span>(<span class="ident">e</span>) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">e</span>),
};
<span class="kw">return</span> <span class="ident">ret</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">FuturesUnordered</span><span class="op"><</span><span class="ident">T</span><span class="op">></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">"FuturesUnordered {{ ... }}"</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">FuturesUnordered</span><span class="op"><</span><span class="ident">T</span><span class="op">></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">// When a `FuturesUnordered` is dropped we want to drop all futures associated</span>
<span class="comment">// with it. At the same time though there may be tons of `Task` handles</span>
<span class="comment">// flying around which contain `Node<T>` references inside them. We'll</span>
<span class="comment">// let those naturally get deallocated when the `Task` itself goes out</span>
<span class="comment">// of scope or gets notified.</span>
<span class="kw">unsafe</span> {
<span class="kw">while</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">head_all</span>.<span class="ident">is_null</span>() {
<span class="kw">let</span> <span class="ident">head</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">head_all</span>;
<span class="kw">let</span> <span class="ident">node</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">unlink</span>(<span class="ident">head</span>);
<span class="self">self</span>.<span class="ident">release_node</span>(<span class="ident">node</span>);
}
}
<span class="comment">// Note that at this point we could still have a bunch of nodes in the</span>
<span class="comment">// mpsc queue. None of those nodes, however, have futures associated</span>
<span class="comment">// with them so they're safe to destroy on any thread. At this point</span>
<span class="comment">// the `FuturesUnordered` struct, the onwer of the one strong reference</span>
<span class="comment">// to `Inner<T>` will drop the strong reference. At that point</span>
<span class="comment">// whichever thread releases the strong refcuont last (be it this</span>
<span class="comment">// thread or some other thread as part of an `upgrade`) will clear out</span>
<span class="comment">// the mpsc queue and free all remaining nodes.</span>
<span class="comment">//</span>
<span class="comment">// While that freeing operation isn't guaranteed to happen here, it's</span>
<span class="comment">// guaranteed to happen "promptly" as no more "blocking work" will</span>
<span class="comment">// happen while there's a strong refcount held.</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// The enqueue function from the 1024cores intrusive MPSC queue algorithm.</span>
<span class="kw">fn</span> <span class="ident">enqueue</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">node</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) {
<span class="kw">unsafe</span> {
<span class="macro">debug_assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="ident">node</span>).<span class="ident">queued</span>.<span class="ident">load</span>(<span class="ident">Relaxed</span>));
<span class="comment">// This action does not require any coordination</span>
(<span class="kw-2">*</span><span class="ident">node</span>).<span class="ident">next_readiness</span>.<span class="ident">store</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>(), <span class="ident">Relaxed</span>);
<span class="comment">// Note that these atomic orderings come from 1024cores</span>
<span class="kw">let</span> <span class="ident">node</span> <span class="op">=</span> <span class="ident">node</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> _;
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">head_readiness</span>.<span class="ident">swap</span>(<span class="ident">node</span>, <span class="ident">AcqRel</span>);
(<span class="kw-2">*</span><span class="ident">prev</span>).<span class="ident">next_readiness</span>.<span class="ident">store</span>(<span class="ident">node</span>, <span class="ident">Release</span>);
}
}
<span class="doccomment">/// The dequeue function from the 1024cores intrusive MPSC queue algorithm</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that this unsafe as it required mutual exclusion (only one thread</span>
<span class="doccomment">/// can call this) to be guaranteed elsewhere.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">dequeue</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Dequeue</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">tail</span> <span class="op">=</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">tail_readiness</span>.<span class="ident">get</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">next</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">tail</span>).<span class="ident">next_readiness</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>);
<span class="kw">if</span> <span class="ident">tail</span> <span class="op">==</span> <span class="self">self</span>.<span class="ident">stub</span>() {
<span class="kw">if</span> <span class="ident">next</span>.<span class="ident">is_null</span>() {
<span class="kw">return</span> <span class="ident">Dequeue</span>::<span class="ident">Empty</span>;
}
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">tail_readiness</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">next</span>;
<span class="ident">tail</span> <span class="op">=</span> <span class="ident">next</span>;
<span class="ident">next</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">next</span>).<span class="ident">next_readiness</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>);
}
<span class="kw">if</span> <span class="op">!</span><span class="ident">next</span>.<span class="ident">is_null</span>() {
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">tail_readiness</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">next</span>;
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">tail</span> <span class="op">!=</span> <span class="self">self</span>.<span class="ident">stub</span>());
<span class="kw">return</span> <span class="ident">Dequeue</span>::<span class="ident">Data</span>(<span class="ident">tail</span>);
}
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">head_readiness</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>) <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> _ <span class="op">!=</span> <span class="ident">tail</span> {
<span class="kw">return</span> <span class="ident">Dequeue</span>::<span class="ident">Inconsistent</span>;
}
<span class="self">self</span>.<span class="ident">enqueue</span>(<span class="self">self</span>.<span class="ident">stub</span>());
<span class="ident">next</span> <span class="op">=</span> (<span class="kw-2">*</span><span class="ident">tail</span>).<span class="ident">next_readiness</span>.<span class="ident">load</span>(<span class="ident">Acquire</span>);
<span class="kw">if</span> <span class="op">!</span><span class="ident">next</span>.<span class="ident">is_null</span>() {
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">tail_readiness</span>.<span class="ident">get</span>() <span class="op">=</span> <span class="ident">next</span>;
<span class="kw">return</span> <span class="ident">Dequeue</span>::<span class="ident">Data</span>(<span class="ident">tail</span>);
}
<span class="ident">Dequeue</span>::<span class="ident">Inconsistent</span>
}
<span class="kw">fn</span> <span class="ident">stub</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">stub</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">></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">// Once we're in the destructor for `Inner<T>` we need to clear out the</span>
<span class="comment">// mpsc queue of nodes if there's anything left in there.</span>
<span class="comment">//</span>
<span class="comment">// Note that each node has a strong reference count associated with it</span>
<span class="comment">// which is owned by the mpsc queue. All nodes should have had their</span>
<span class="comment">// futures dropped already by the `FuturesUnordered` destructor above,</span>
<span class="comment">// so we're just pulling out nodes and dropping their refcounts.</span>
<span class="kw">unsafe</span> {
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">dequeue</span>() {
<span class="ident">Dequeue</span>::<span class="ident">Empty</span> <span class="op">=></span> <span class="kw">break</span>,
<span class="ident">Dequeue</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> <span class="ident">abort</span>(<span class="string">"inconsistent in drop"</span>),
<span class="ident">Dequeue</span>::<span class="ident">Data</span>(<span class="ident">ptr</span>) <span class="op">=></span> <span class="ident">drop</span>(<span class="ident">ptr2arc</span>(<span class="ident">ptr</span>)),
}
}
}
}
}
<span class="attribute">#[<span class="ident">allow</span>(<span class="ident">missing_debug_implementations</span>)]</span>
<span class="kw">struct</span> <span class="ident">NodeToHandle</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="lifetime">'a</span><span class="op">></span>(<span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</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">'a</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">NodeToHandle</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="ident">NodeToHandle</span>(<span class="self">self</span>.<span class="number">0</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">NodeToHandle</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">NotifyHandle</span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">handle</span>: <span class="ident">NodeToHandle</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">NotifyHandle</span> {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">handle</span>.<span class="number">0</span>.<span class="ident">clone</span>();
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">mem</span>::<span class="ident">transmute</span>::<span class="op"><</span><span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</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="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>(<span class="ident">ptr</span>);
<span class="ident">NotifyHandle</span>::<span class="ident">new</span>(<span class="ident">hide_lt</span>(<span class="ident">ptr</span>))
}
}
}
<span class="kw">struct</span> <span class="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">PhantomData</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>);
<span class="comment">// We should never touch `T` on any thread other than the one owning</span>
<span class="comment">// `FuturesUnordered`, so this should be a safe operation.</span>
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">ArcNode</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">Notify</span> <span class="kw">for</span> <span class="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">notify</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">_id</span>: <span class="ident">usize</span>) {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">me</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">ArcNode</span><span class="op"><</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">me</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="op">=</span> <span class="kw-2">&</span><span class="ident">me</span>;
<span class="kw">let</span> <span class="ident">me</span> <span class="op">=</span> <span class="ident">me</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>;
<span class="ident">Node</span>::<span class="ident">notify</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">me</span>)
}
}
}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">UnsafeNotify</span> <span class="kw">for</span> <span class="ident">ArcNode</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">clone_raw</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">NotifyHandle</span> {
<span class="kw">let</span> <span class="ident">me</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">ArcNode</span><span class="op"><</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">me</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="op">=</span> <span class="kw-2">&</span><span class="ident">me</span>;
<span class="kw">let</span> <span class="ident">me</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">*</span>(<span class="ident">me</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>);
<span class="ident">NodeToHandle</span>(<span class="ident">me</span>).<span class="ident">into</span>()
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">drop_raw</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">me</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">ArcNode</span><span class="op"><</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">me</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">me</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>;
<span class="ident">ptr</span>::<span class="ident">drop_in_place</span>(<span class="ident">me</span>);
}
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">hide_lt</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">p</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">ArcNode</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">UnsafeNotify</span> {
<span class="ident">mem</span>::<span class="ident">transmute</span>(<span class="ident">p</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">UnsafeNotify</span>)
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">notify</span>(<span class="ident">me</span>: <span class="kw-2">&</span><span class="ident">Arc</span><span class="op"><</span><span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>) {
<span class="kw">let</span> <span class="ident">inner</span> <span class="op">=</span> <span class="kw">match</span> <span class="ident">me</span>.<span class="ident">queue</span>.<span class="ident">upgrade</span>() {
<span class="prelude-val">Some</span>(<span class="ident">inner</span>) <span class="op">=></span> <span class="ident">inner</span>,
<span class="prelude-val">None</span> <span class="op">=></span> <span class="kw">return</span>,
};
<span class="comment">// It's our job to notify the node that it's ready to get polled,</span>
<span class="comment">// meaning that we need to enqueue it into the readiness queue. To</span>
<span class="comment">// do this we flag that we're ready to be queued, and if successful</span>
<span class="comment">// we then do the literal queueing operation, ensuring that we're</span>
<span class="comment">// only queued once.</span>
<span class="comment">//</span>
<span class="comment">// Once the node is inserted we be sure to notify the parent task,</span>
<span class="comment">// as it'll want to come along and pick up our node now.</span>
<span class="comment">//</span>
<span class="comment">// Note that we don't change the reference count of the node here,</span>
<span class="comment">// we're just enqueueing the raw pointer. The `FuturesUnordered`</span>
<span class="comment">// implementation guarantees that if we set the `queued` flag true that</span>
<span class="comment">// there's a reference count held by the main `FuturesUnordered` queue</span>
<span class="comment">// still.</span>
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="ident">me</span>.<span class="ident">queued</span>.<span class="ident">swap</span>(<span class="bool-val">true</span>, <span class="ident">SeqCst</span>);
<span class="kw">if</span> <span class="op">!</span><span class="ident">prev</span> {
<span class="ident">inner</span>.<span class="ident">enqueue</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="ident">me</span>);
<span class="ident">inner</span>.<span class="ident">parent</span>.<span class="ident">notify</span>();
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Node</span><span class="op"><</span><span class="ident">T</span><span class="op">></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">// Currently a `Node<T>` is sent across all threads for any lifetime,</span>
<span class="comment">// regardless of `T`. This means that for memory safety we can't</span>
<span class="comment">// actually touch `T` at any time except when we have a reference to the</span>
<span class="comment">// `FuturesUnordered` itself.</span>
<span class="comment">//</span>
<span class="comment">// Consequently it *should* be the case that we always drop futures from</span>
<span class="comment">// the `FuturesUnordered` instance, but this is a bomb in place to catch</span>
<span class="comment">// any bugs in that logic.</span>
<span class="kw">unsafe</span> {
<span class="kw">if</span> (<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">future</span>.<span class="ident">get</span>()).<span class="ident">is_some</span>() {
<span class="ident">abort</span>(<span class="string">"future still here when dropping"</span>);
}
}
}
}
<span class="kw">fn</span> <span class="ident">arc2ptr</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">ptr</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span> {
<span class="kw">let</span> <span class="ident">addr</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">ptr</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span>;
<span class="ident">mem</span>::<span class="ident">forget</span>(<span class="ident">ptr</span>);
<span class="kw">return</span> <span class="ident">addr</span>
}
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">ptr2arc</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span>) <span class="op">-></span> <span class="ident">Arc</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">anchor</span> <span class="op">=</span> <span class="ident">mem</span>::<span class="ident">transmute</span>::<span class="op"><</span><span class="ident">usize</span>, <span class="ident">Arc</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>(<span class="number">0x10</span>);
<span class="kw">let</span> <span class="ident">addr</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">*</span><span class="ident">anchor</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span>;
<span class="ident">mem</span>::<span class="ident">forget</span>(<span class="ident">anchor</span>);
<span class="kw">let</span> <span class="ident">offset</span> <span class="op">=</span> <span class="ident">addr</span> <span class="kw">as</span> <span class="ident">isize</span> <span class="op">-</span> <span class="number">0x10</span>;
<span class="ident">mem</span>::<span class="ident">transmute</span>::<span class="op"><</span><span class="ident">isize</span>, <span class="ident">Arc</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>(<span class="ident">ptr</span> <span class="kw">as</span> <span class="ident">isize</span> <span class="op">-</span> <span class="ident">offset</span>)
}
<span class="kw">fn</span> <span class="ident">abort</span>(<span class="ident">s</span>: <span class="kw-2">&</span><span class="ident">str</span>) <span class="op">-></span> <span class="op">!</span> {
<span class="kw">struct</span> <span class="ident">DoublePanic</span>;
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">DoublePanic</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="macro">panic</span><span class="macro">!</span>(<span class="string">"panicking twice to abort the program"</span>);
}
}
<span class="kw">let</span> <span class="ident">_bomb</span> <span class="op">=</span> <span class="ident">DoublePanic</span>;
<span class="macro">panic</span><span class="macro">!</span>(<span class="string">"{}"</span>, <span class="ident">s</span>);
}
</pre>
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