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</pre><pre class="rust ">
<span class="doccomment">//! A one-shot, futures-aware channel</span>
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">Arc</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">sync</span>::<span class="ident">atomic</span>::<span class="ident">AtomicBool</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">SeqCst</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>;
<span class="kw">use</span> {<span class="ident">Future</span>, <span class="ident">Poll</span>, <span class="ident">Async</span>};
<span class="kw">use</span> <span class="ident">future</span>::{<span class="ident">lazy</span>, <span class="ident">Lazy</span>, <span class="ident">Executor</span>, <span class="ident">IntoFuture</span>};
<span class="kw">use</span> <span class="ident">lock</span>::<span class="ident">Lock</span>;
<span class="kw">use</span> <span class="ident">task</span>::{<span class="self">self</span>, <span class="ident">Task</span>};
<span class="doccomment">/// A future representing the completion of a computation happening elsewhere in</span>
<span class="doccomment">/// memory.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is created by the `oneshot::channel` function.</span>
<span class="attribute">#[<span class="ident">must_use</span> <span class="op">=</span> <span class="string">"futures do nothing unless polled"</span>]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</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">T</span><span class="op">>></span>,
}
<span class="doccomment">/// Represents the completion half of a oneshot through which the result of a</span>
<span class="doccomment">/// computation is signaled.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is created by the `oneshot::channel` function.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Sender</span><span class="op"><</span><span class="ident">T</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">T</span><span class="op">>></span>,
}
<span class="doccomment">/// Internal state of the `Receiver`/`Sender` pair above. This is all used as</span>
<span class="doccomment">/// the internal synchronization between the two for send/recv operations.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</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="doccomment">/// Indicates whether this oneshot is complete yet. This is filled in both</span>
<span class="doccomment">/// by `Sender::drop` and by `Receiver::drop`, and both sides iterpret it</span>
<span class="doccomment">/// appropriately.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For `Receiver`, if this is `true`, then it's guaranteed that `data` is</span>
<span class="doccomment">/// unlocked and ready to be inspected.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For `Sender` if this is `true` then the oneshot has gone away and it</span>
<span class="doccomment">/// can return ready from `poll_cancel`.</span>
<span class="ident">complete</span>: <span class="ident">AtomicBool</span>,
<span class="doccomment">/// The actual data being transferred as part of this `Receiver`. This is</span>
<span class="doccomment">/// filled in by `Sender::complete` and read by `Receiver::poll`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that this is protected by `Lock`, but it is in theory safe to</span>
<span class="doccomment">/// replace with an `UnsafeCell` as it's actually protected by `complete`</span>
<span class="doccomment">/// above. I wouldn't recommend doing this, however, unless someone is</span>
<span class="doccomment">/// supremely confident in the various atomic orderings here and there.</span>
<span class="ident">data</span>: <span class="ident">Lock</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="doccomment">/// Field to store the task which is blocked in `Receiver::poll`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is filled in when a oneshot is polled but not ready yet. Note that</span>
<span class="doccomment">/// the `Lock` here, unlike in `data` above, is important to resolve races.</span>
<span class="doccomment">/// Both the `Receiver` and the `Sender` halves understand that if they</span>
<span class="doccomment">/// can't acquire the lock then some important interference is happening.</span>
<span class="ident">rx_task</span>: <span class="ident">Lock</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Task</span><span class="op">>></span>,
<span class="doccomment">/// Like `rx_task` above, except for the task blocked in</span>
<span class="doccomment">/// `Sender::poll_cancel`. Additionally, `Lock` cannot be `UnsafeCell`.</span>
<span class="ident">tx_task</span>: <span class="ident">Lock</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Task</span><span class="op">>></span>,
}
<span class="doccomment">/// Creates a new futures-aware, one-shot channel.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is similar to Rust's channels found in the standard library.</span>
<span class="doccomment">/// Two halves are returned, the first of which is a `Sender` handle, used to</span>
<span class="doccomment">/// signal the end of a computation and provide its value. The second half is a</span>
<span class="doccomment">/// `Receiver` which implements the `Future` trait, resolving to the value that</span>
<span class="doccomment">/// was given to the `Sender` handle.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Each half can be separately owned and sent across threads/tasks.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::thread;</span>
<span class="doccomment">/// use futures::sync::oneshot;</span>
<span class="doccomment">/// use futures::*;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let (c, p) = oneshot::channel::<i32>();</span>
<span class="doccomment">///</span>
<span class="doccomment">/// thread::spawn(|| {</span>
<span class="doccomment">/// p.map(|i| {</span>
<span class="doccomment">/// println!("got: {}", i);</span>
<span class="doccomment">/// }).wait();</span>
<span class="doccomment">/// });</span>
<span class="doccomment">///</span>
<span class="doccomment">/// c.send(3).unwrap();</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">channel</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">-></span> (<span class="ident">Sender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">Receiver</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">new</span>());
<span class="kw">let</span> <span class="ident">receiver</span> <span class="op">=</span> <span class="ident">Receiver</span> {
<span class="ident">inner</span>: <span class="ident">inner</span>.<span class="ident">clone</span>(),
};
<span class="kw">let</span> <span class="ident">sender</span> <span class="op">=</span> <span class="ident">Sender</span> {
<span class="ident">inner</span>: <span class="ident">inner</span>,
};
(<span class="ident">sender</span>, <span class="ident">receiver</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="kw">fn</span> <span class="ident">new</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="ident">Inner</span> {
<span class="ident">complete</span>: <span class="ident">AtomicBool</span>::<span class="ident">new</span>(<span class="bool-val">false</span>),
<span class="ident">data</span>: <span class="ident">Lock</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>),
<span class="ident">rx_task</span>: <span class="ident">Lock</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>),
<span class="ident">tx_task</span>: <span class="ident">Lock</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>),
}
}
<span class="kw">fn</span> <span class="ident">send</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">T</span><span class="op">></span> {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">t</span>)
}
<span class="comment">// Note that this lock acquisition should always succeed as it can only</span>
<span class="comment">// interfere with `poll` in `Receiver` which is only called when the</span>
<span class="comment">// `complete` flag is true, which we're setting here.</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">slot</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">data</span>.<span class="ident">try_lock</span>().<span class="ident">unwrap</span>();
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">slot</span>.<span class="ident">is_none</span>());
<span class="kw-2">*</span><span class="ident">slot</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">t</span>);
<span class="ident">drop</span>(<span class="ident">slot</span>);
<span class="prelude-val">Ok</span>(())
}
<span class="kw">fn</span> <span class="ident">poll_cancel</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span>(), ()<span class="op">></span> {
<span class="comment">// Fast path up first, just read the flag and see if our other half is</span>
<span class="comment">// gone. This flag is set both in our destructor and the oneshot</span>
<span class="comment">// destructor, but our destructor hasn't run yet so if it's set then the</span>
<span class="comment">// oneshot is gone.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(()))
}
<span class="comment">// If our other half is not gone then we need to park our current task</span>
<span class="comment">// and move it into the `notify_cancel` slot to get notified when it's</span>
<span class="comment">// actually gone.</span>
<span class="comment">//</span>
<span class="comment">// If `try_lock` fails, then the `Receiver` is in the process of using</span>
<span class="comment">// it, so we can deduce that it's now in the process of going away and</span>
<span class="comment">// hence we're canceled. If it succeeds then we just store our handle.</span>
<span class="comment">//</span>
<span class="comment">// Crucially we then check `oneshot_gone` *again* before we return.</span>
<span class="comment">// While we were storing our handle inside `notify_cancel` the `Receiver`</span>
<span class="comment">// may have been dropped. The first thing it does is set the flag, and</span>
<span class="comment">// if it fails to acquire the lock it assumes that we'll see the flag</span>
<span class="comment">// later on. So... we then try to see the flag later on!</span>
<span class="kw">let</span> <span class="ident">handle</span> <span class="op">=</span> <span class="ident">task</span>::<span class="ident">current</span>();
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">tx_task</span>.<span class="ident">try_lock</span>() {
<span class="prelude-val">Some</span>(<span class="kw-2">mut</span> <span class="ident">p</span>) <span class="op">=></span> <span class="kw-2">*</span><span class="ident">p</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">handle</span>),
<span class="prelude-val">None</span> <span class="op">=></span> <span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(())),
}
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(()))
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>)
}
}
<span class="kw">fn</span> <span class="ident">drop_tx</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// Flag that we're a completed `Sender` and try to wake up a receiver.</span>
<span class="comment">// Whether or not we actually stored any data will get picked up and</span>
<span class="comment">// translated to either an item or cancellation.</span>
<span class="comment">//</span>
<span class="comment">// Note that if we fail to acquire the `rx_task` lock then that means</span>
<span class="comment">// we're in one of two situations:</span>
<span class="comment">//</span>
<span class="comment">// 1. The receiver is trying to block in `poll`</span>
<span class="comment">// 2. The receiver is being dropped</span>
<span class="comment">//</span>
<span class="comment">// In the first case it'll check the `complete` flag after it's done</span>
<span class="comment">// blocking to see if it succeeded. In the latter case we don't need to</span>
<span class="comment">// wake up anyone anyway. So in both cases it's ok to ignore the `None`</span>
<span class="comment">// case of `try_lock` and bail out.</span>
<span class="comment">//</span>
<span class="comment">// The first case crucially depends on `Lock` using `SeqCst` ordering</span>
<span class="comment">// under the hood. If it instead used `Release` / `Acquire` ordering,</span>
<span class="comment">// then it would not necessarily synchronize with `inner.complete`</span>
<span class="comment">// and deadlock might be possible, as was observed in</span>
<span class="comment">// https://github.com/alexcrichton/futures-rs/pull/219.</span>
<span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">store</span>(<span class="bool-val">true</span>, <span class="ident">SeqCst</span>);
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="kw-2">mut</span> <span class="ident">slot</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">rx_task</span>.<span class="ident">try_lock</span>() {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">task</span>) <span class="op">=</span> <span class="ident">slot</span>.<span class="ident">take</span>() {
<span class="ident">drop</span>(<span class="ident">slot</span>);
<span class="ident">task</span>.<span class="ident">notify</span>();
}
}
}
<span class="kw">fn</span> <span class="ident">close_rx</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// Flag our completion and then attempt to wake up the sender if it's</span>
<span class="comment">// blocked. See comments in `drop` below for more info</span>
<span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">store</span>(<span class="bool-val">true</span>, <span class="ident">SeqCst</span>);
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="kw-2">mut</span> <span class="ident">handle</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">tx_task</span>.<span class="ident">try_lock</span>() {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">task</span>) <span class="op">=</span> <span class="ident">handle</span>.<span class="ident">take</span>() {
<span class="ident">drop</span>(<span class="ident">handle</span>);
<span class="ident">task</span>.<span class="ident">notify</span>()
}
}
}
<span class="kw">fn</span> <span class="ident">recv</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Canceled</span><span class="op">></span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">done</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="comment">// Check to see if some data has arrived. If it hasn't then we need to</span>
<span class="comment">// block our task.</span>
<span class="comment">//</span>
<span class="comment">// Note that the acquisition of the `rx_task` lock might fail below, but</span>
<span class="comment">// the only situation where this can happen is during `Sender::drop`</span>
<span class="comment">// when we are indeed completed already. If that's happening then we</span>
<span class="comment">// know we're completed so keep going.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) {
<span class="ident">done</span> <span class="op">=</span> <span class="bool-val">true</span>;
} <span class="kw">else</span> {
<span class="kw">let</span> <span class="ident">task</span> <span class="op">=</span> <span class="ident">task</span>::<span class="ident">current</span>();
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">rx_task</span>.<span class="ident">try_lock</span>() {
<span class="prelude-val">Some</span>(<span class="kw-2">mut</span> <span class="ident">slot</span>) <span class="op">=></span> <span class="kw-2">*</span><span class="ident">slot</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">task</span>),
<span class="prelude-val">None</span> <span class="op">=></span> <span class="ident">done</span> <span class="op">=</span> <span class="bool-val">true</span>,
}
}
<span class="comment">// If we're `done` via one of the paths above, then look at the data and</span>
<span class="comment">// figure out what the answer is. If, however, we stored `rx_task`</span>
<span class="comment">// successfully above we need to check again if we're completed in case</span>
<span class="comment">// a message was sent while `rx_task` was locked and couldn't notify us</span>
<span class="comment">// otherwise.</span>
<span class="comment">//</span>
<span class="comment">// If we're not done, and we're not complete, though, then we've</span>
<span class="comment">// successfully blocked our task and we return `NotReady`.</span>
<span class="kw">if</span> <span class="ident">done</span> <span class="op">||</span> <span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">data</span>.<span class="ident">try_lock</span>().<span class="ident">unwrap</span>().<span class="ident">take</span>() {
<span class="prelude-val">Some</span>(<span class="ident">data</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">data</span>.<span class="ident">into</span>()),
<span class="prelude-val">None</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Canceled</span>),
}
} <span class="kw">else</span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>)
}
}
<span class="kw">fn</span> <span class="ident">drop_rx</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// Indicate to the `Sender` that we're done, so any future calls to</span>
<span class="comment">// `poll_cancel` are weeded out.</span>
<span class="self">self</span>.<span class="ident">complete</span>.<span class="ident">store</span>(<span class="bool-val">true</span>, <span class="ident">SeqCst</span>);
<span class="comment">// If we've blocked a task then there's no need for it to stick around,</span>
<span class="comment">// so we need to drop it. If this lock acquisition fails, though, then</span>
<span class="comment">// it's just because our `Sender` is trying to take the task, so we</span>
<span class="comment">// let them take care of that.</span>
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="kw-2">mut</span> <span class="ident">slot</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">rx_task</span>.<span class="ident">try_lock</span>() {
<span class="kw">let</span> <span class="ident">task</span> <span class="op">=</span> <span class="ident">slot</span>.<span class="ident">take</span>();
<span class="ident">drop</span>(<span class="ident">slot</span>);
<span class="ident">drop</span>(<span class="ident">task</span>);
}
<span class="comment">// Finally, if our `Sender` wants to get notified of us going away, it</span>
<span class="comment">// would have stored something in `tx_task`. Here we try to peel that</span>
<span class="comment">// out and unpark it.</span>
<span class="comment">//</span>
<span class="comment">// Note that the `try_lock` here may fail, but only if the `Sender` is</span>
<span class="comment">// in the process of filling in the task. If that happens then we</span>
<span class="comment">// already flagged `complete` and they'll pick that up above.</span>
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="kw-2">mut</span> <span class="ident">handle</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">tx_task</span>.<span class="ident">try_lock</span>() {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">task</span>) <span class="op">=</span> <span class="ident">handle</span>.<span class="ident">take</span>() {
<span class="ident">drop</span>(<span class="ident">handle</span>);
<span class="ident">task</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">Sender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="attribute">#[<span class="ident">deprecated</span>(<span class="ident">note</span> <span class="op">=</span> <span class="string">"renamed to `send`"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"0.1.11"</span>)]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"with-deprecated"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">complete</span>(<span class="self">self</span>, <span class="ident">t</span>: <span class="ident">T</span>) {
<span class="ident">drop</span>(<span class="self">self</span>.<span class="ident">send</span>(<span class="ident">t</span>));
}
<span class="doccomment">/// Completes this oneshot with a successful result.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function will consume `self` and indicate to the other end, the</span>
<span class="doccomment">/// `Receiver`, that the value provided is the result of the computation this</span>
<span class="doccomment">/// represents.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the value is successfully enqueued for the remote end to receive,</span>
<span class="doccomment">/// then `Ok(())` is returned. If the receiving end was deallocated before</span>
<span class="doccomment">/// this function was called, however, then `Err` is returned with the value</span>
<span class="doccomment">/// provided.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">send</span>(<span class="self">self</span>, <span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">T</span><span class="op">></span> {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">send</span>(<span class="ident">t</span>)
}
<span class="doccomment">/// Polls this `Sender` half to detect whether the `Receiver` this has</span>
<span class="doccomment">/// paired with has gone away.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function can be used to learn about when the `Receiver` (consumer)</span>
<span class="doccomment">/// half has gone away and nothing will be able to receive a message sent</span>
<span class="doccomment">/// from `complete`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Like `Future::poll`, this function will panic if it's not called from</span>
<span class="doccomment">/// within the context of a task. In otherwords, this should only ever be</span>
<span class="doccomment">/// called from inside another future.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If `Ready` is returned then it means that the `Receiver` has disappeared</span>
<span class="doccomment">/// and the result this `Sender` would otherwise produce should no longer</span>
<span class="doccomment">/// be produced.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If `NotReady` is returned then the `Receiver` is still alive and may be</span>
<span class="doccomment">/// able to receive a message if sent. The current task, however, is</span>
<span class="doccomment">/// scheduled to receive a notification if the corresponding `Receiver` goes</span>
<span class="doccomment">/// away.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">poll_cancel</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="op">></span> {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">poll_cancel</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">Sender</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="self">self</span>.<span class="ident">inner</span>.<span class="ident">drop_tx</span>()
}
}
<span class="doccomment">/// Error returned from a `Receiver<T>` whenever the correponding `Sender<T>`</span>
<span class="doccomment">/// is dropped.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Copy</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Canceled</span>;
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">Canceled</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">"oneshot canceled"</span>)
}
}
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">Canceled</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"oneshot canceled"</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Gracefully close this receiver, preventing sending any future messages.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Any `send` operation which happens after this method returns is</span>
<span class="doccomment">/// guaranteed to fail. Once this method is called the normal `poll` method</span>
<span class="doccomment">/// can be used to determine whether a message was actually sent or not. If</span>
<span class="doccomment">/// `Canceled` is returned from `poll` then no message was sent.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">close</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">close_rx</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">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">type</span> <span class="ident">Error</span> <span class="op">=</span> <span class="ident">Canceled</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="ident">T</span>, <span class="ident">Canceled</span><span class="op">></span> {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">recv</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">Receiver</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="self">self</span>.<span class="ident">inner</span>.<span class="ident">drop_rx</span>()
}
}
<span class="doccomment">/// Handle returned from the `spawn` function.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This handle is a future representing the completion of a different future on</span>
<span class="doccomment">/// a separate executor. Created through the `oneshot::spawn` function this</span>
<span class="doccomment">/// handle will resolve when the future provided to `spawn` resolves on the</span>
<span class="doccomment">/// `Executor` instance provided to that function.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this handle is dropped then the future will automatically no longer be</span>
<span class="doccomment">/// polled and is scheduled to be dropped. This can be canceled with the</span>
<span class="doccomment">/// `forget` function, however.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">SpawnHandle</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> {
<span class="ident">rx</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">ExecuteInner</span><span class="op"><</span><span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">>></span><span class="op">></span>,
}
<span class="kw">struct</span> <span class="ident">ExecuteInner</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">inner</span>: <span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">keep_running</span>: <span class="ident">AtomicBool</span>,
}
<span class="doccomment">/// Type of future which `Execute` instances below must be able to spawn.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Execute</span><span class="op"><</span><span class="ident">F</span>: <span class="ident">Future</span><span class="op">></span> {
<span class="ident">future</span>: <span class="ident">F</span>,
<span class="ident">tx</span>: <span class="ident">Arc</span><span class="op"><</span><span class="ident">ExecuteInner</span><span class="op"><</span><span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">F</span>::<span class="ident">Item</span>, <span class="ident">F</span>::<span class="ident">Error</span><span class="op">>></span><span class="op">></span>,
}
<span class="doccomment">/// Spawns a `future` onto the instance of `Executor` provided, `executor`,</span>
<span class="doccomment">/// returning a handle representing the completion of the future.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `SpawnHandle` returned is a future that is a proxy for `future` itself.</span>
<span class="doccomment">/// When `future` completes on `executor` then the `SpawnHandle` will itself be</span>
<span class="doccomment">/// resolved. Internally `SpawnHandle` contains a `oneshot` channel and is</span>
<span class="doccomment">/// thus safe to send across threads.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `future` will be canceled if the `SpawnHandle` is dropped. If this is</span>
<span class="doccomment">/// not desired then the `SpawnHandle::forget` function can be used to continue</span>
<span class="doccomment">/// running the future to completion.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function will panic if the instance of `Spawn` provided is unable to</span>
<span class="doccomment">/// spawn the `future` provided.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the provided instance of `Spawn` does not actually run `future` to</span>
<span class="doccomment">/// completion, then the returned handle may panic when polled. Typically this</span>
<span class="doccomment">/// is not a problem, though, as most instances of `Spawn` will run futures to</span>
<span class="doccomment">/// completion.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that the returned future will likely panic if the `futures` provided</span>
<span class="doccomment">/// panics. If a future running on an executor panics that typically means that</span>
<span class="doccomment">/// the executor drops the future, which falls into the above case of not</span>
<span class="doccomment">/// running the future to completion essentially.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">spawn</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">E</span><span class="op">></span>(<span class="ident">future</span>: <span class="ident">F</span>, <span class="ident">executor</span>: <span class="kw-2">&</span><span class="ident">E</span>) <span class="op">-></span> <span class="ident">SpawnHandle</span><span class="op"><</span><span class="ident">F</span>::<span class="ident">Item</span>, <span class="ident">F</span>::<span class="ident">Error</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">Future</span>,
<span class="ident">E</span>: <span class="ident">Executor</span><span class="op"><</span><span class="ident">Execute</span><span class="op"><</span><span class="ident">F</span><span class="op">>></span>,
{
<span class="kw">let</span> <span class="ident">data</span> <span class="op">=</span> <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">ExecuteInner</span> {
<span class="ident">inner</span>: <span class="ident">Inner</span>::<span class="ident">new</span>(),
<span class="ident">keep_running</span>: <span class="ident">AtomicBool</span>::<span class="ident">new</span>(<span class="bool-val">true</span>),
});
<span class="ident">executor</span>.<span class="ident">execute</span>(<span class="ident">Execute</span> {
<span class="ident">future</span>: <span class="ident">future</span>,
<span class="ident">tx</span>: <span class="ident">data</span>.<span class="ident">clone</span>(),
}).<span class="ident">expect</span>(<span class="string">"failed to spawn future"</span>);
<span class="ident">SpawnHandle</span> { <span class="ident">rx</span>: <span class="ident">data</span> }
}
<span class="doccomment">/// Spawns a function `f` onto the `Spawn` instance provided `s`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For more information see the `spawn` function in this module. This function</span>
<span class="doccomment">/// is just a thin wrapper around `spawn` which will execute the closure on the</span>
<span class="doccomment">/// executor provided and then complete the future that the closure returns.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">spawn_fn</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span>, <span class="ident">E</span><span class="op">></span>(<span class="ident">f</span>: <span class="ident">F</span>, <span class="ident">executor</span>: <span class="kw-2">&</span><span class="ident">E</span>) <span class="op">-></span> <span class="ident">SpawnHandle</span><span class="op"><</span><span class="ident">R</span>::<span class="ident">Item</span>, <span class="ident">R</span>::<span class="ident">Error</span><span class="op">></span>
<span class="kw">where</span> <span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-></span> <span class="ident">R</span>,
<span class="ident">R</span>: <span class="ident">IntoFuture</span>,
<span class="ident">E</span>: <span class="ident">Executor</span><span class="op"><</span><span class="ident">Execute</span><span class="op"><</span><span class="ident">Lazy</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">>></span><span class="op">></span>,
{
<span class="ident">spawn</span>(<span class="ident">lazy</span>(<span class="ident">f</span>), <span class="ident">executor</span>)
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> <span class="ident">SpawnHandle</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> {
<span class="doccomment">/// Drop this future without canceling the underlying future.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// When `SpawnHandle` is dropped, the spawned future will be canceled as</span>
<span class="doccomment">/// well if the future hasn't already resolved. This function can be used</span>
<span class="doccomment">/// when to drop this future but keep executing the underlying future.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">forget</span>(<span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">rx</span>.<span class="ident">keep_running</span>.<span class="ident">store</span>(<span class="bool-val">false</span>, <span class="ident">SeqCst</span>);
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> <span class="ident">Future</span> <span class="kw">for</span> <span class="ident">SpawnHandle</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">type</span> <span class="ident">Error</span> <span class="op">=</span> <span class="ident">E</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="ident">T</span>, <span class="ident">E</span><span class="op">></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">rx</span>.<span class="ident">inner</span>.<span class="ident">recv</span>() {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="prelude-val">Ok</span>(<span class="ident">t</span>))) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">t</span>.<span class="ident">into</span>()),
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</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="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>),
<span class="prelude-val">Err</span>(_) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"future was canceled before completion"</span>),
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">fmt</span>::<span class="ident">Debug</span>, <span class="ident">E</span>: <span class="ident">fmt</span>::<span class="ident">Debug</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">SpawnHandle</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</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">f</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="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"SpawnHandle"</span>)
.<span class="ident">finish</span>()
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">SpawnHandle</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</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="self">self</span>.<span class="ident">rx</span>.<span class="ident">inner</span>.<span class="ident">drop_rx</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">Future</span> <span class="kw">for</span> <span class="ident">Execute</span><span class="op"><</span><span class="ident">F</span><span class="op">></span> {
<span class="kw">type</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="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="op">></span> {
<span class="comment">// If we're canceled then we may want to bail out early.</span>
<span class="comment">//</span>
<span class="comment">// If the `forget` function was called, though, then we keep going.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">tx</span>.<span class="ident">inner</span>.<span class="ident">poll_cancel</span>().<span class="ident">unwrap</span>().<span class="ident">is_ready</span>() {
<span class="kw">if</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">tx</span>.<span class="ident">keep_running</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>) {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(().<span class="ident">into</span>())
}
}
<span class="kw">let</span> <span class="ident">result</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">future</span>.<span class="ident">poll</span>() {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>) <span class="op">=></span> <span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>),
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">t</span>)) <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="ident">t</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="ident">drop</span>(<span class="self">self</span>.<span class="ident">tx</span>.<span class="ident">inner</span>.<span class="ident">send</span>(<span class="ident">result</span>));
<span class="prelude-val">Ok</span>(().<span class="ident">into</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">fmt</span>::<span class="ident">Debug</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">Execute</span><span class="op"><</span><span class="ident">F</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">f</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="ident">f</span>.<span class="ident">debug_struct</span>(<span class="string">"Execute"</span>)
.<span class="ident">field</span>(<span class="string">"future"</span>, <span class="kw-2">&</span><span class="self">self</span>.<span class="ident">future</span>)
.<span class="ident">finish</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">Drop</span> <span class="kw">for</span> <span class="ident">Execute</span><span class="op"><</span><span class="ident">F</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="self">self</span>.<span class="ident">tx</span>.<span class="ident">inner</span>.<span class="ident">drop_tx</span>();
}
}
</pre>
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