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</pre><pre class="rust ">
<span class="comment">// Copyright 2014 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="doccomment">/// Oneshot channels/ports</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is the initial flavor of channels/ports used for comm module. This is</span>
<span class="doccomment">/// an optimization for the one-use case of a channel. The major optimization of</span>
<span class="doccomment">/// this type is to have one and exactly one allocation when the chan/port pair</span>
<span class="doccomment">/// is created.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Another possible optimization would be to not use an Arc box because</span>
<span class="doccomment">/// in theory we know when the shared packet can be deallocated (no real need</span>
<span class="doccomment">/// for the atomic reference counting), but I was having trouble how to destroy</span>
<span class="doccomment">/// the data early in a drop of a Port.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Implementation</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Oneshots are implemented around one atomic usize variable. This variable</span>
<span class="doccomment">/// indicates both the state of the port/chan but also contains any threads</span>
<span class="doccomment">/// blocked on the port. All atomic operations happen on this one word.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In order to upgrade a oneshot channel, an upgrade is considered a disconnect</span>
<span class="doccomment">/// on behalf of the channel side of things (it can be mentally thought of as</span>
<span class="doccomment">/// consuming the port). This upgrade is then also stored in the shared packet.</span>
<span class="doccomment">/// The one caveat to consider is that when a port sees a disconnected channel</span>
<span class="doccomment">/// it must check for data because there is no "data plus upgrade" state.</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">Failure</span>::<span class="kw-2">*</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">UpgradeResult</span>::<span class="kw-2">*</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="self">self</span>::<span class="ident">SelectionResult</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="self">self</span>::<span class="ident">MyUpgrade</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">Receiver</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">blocking</span>::{<span class="self">self</span>, <span class="ident">SignalToken</span>};
<span class="kw">use</span> <span class="ident">cell</span>::<span class="ident">UnsafeCell</span>;
<span class="kw">use</span> <span class="ident">ptr</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">atomic</span>::{<span class="ident">AtomicUsize</span>, <span class="ident">Ordering</span>};
<span class="kw">use</span> <span class="ident">time</span>::<span class="ident">Instant</span>;
<span class="comment">// Various states you can find a port in.</span>
<span class="kw">const</span> <span class="ident">EMPTY</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">0</span>; <span class="comment">// initial state: no data, no blocked receiver</span>
<span class="kw">const</span> <span class="ident">DATA</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">1</span>; <span class="comment">// data ready for receiver to take</span>
<span class="kw">const</span> <span class="ident">DISCONNECTED</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">2</span>; <span class="comment">// channel is disconnected OR upgraded</span>
<span class="comment">// Any other value represents a pointer to a SignalToken value. The</span>
<span class="comment">// protocol ensures that when the state moves *to* a pointer,</span>
<span class="comment">// ownership of the token is given to the packet, and when the state</span>
<span class="comment">// moves *from* a pointer, ownership of the token is transferred to</span>
<span class="comment">// whoever changed the state.</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Packet</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="comment">// Internal state of the chan/port pair (stores the blocked thread as well)</span>
<span class="ident">state</span>: <span class="ident">AtomicUsize</span>,
<span class="comment">// One-shot data slot location</span>
<span class="ident">data</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">// when used for the second time, a oneshot channel must be upgraded, and</span>
<span class="comment">// this contains the slot for the upgrade</span>
<span class="ident">upgrade</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">MyUpgrade</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span>,
}
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Failure</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Empty</span>,
<span class="ident">Disconnected</span>,
<span class="ident">Upgraded</span>(<span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>),
}
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">UpgradeResult</span> {
<span class="ident">UpSuccess</span>,
<span class="ident">UpDisconnected</span>,
<span class="ident">UpWoke</span>(<span class="ident">SignalToken</span>),
}
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SelectionResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">SelCanceled</span>,
<span class="ident">SelUpgraded</span>(<span class="ident">SignalToken</span>, <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>),
<span class="ident">SelSuccess</span>,
}
<span class="kw">enum</span> <span class="ident">MyUpgrade</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">NothingSent</span>,
<span class="ident">SendUsed</span>,
<span class="ident">GoUp</span>(<span class="ident">Receiver</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">Packet</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-></span> <span class="ident">Packet</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">Packet</span> {
<span class="ident">data</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>),
<span class="ident">upgrade</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">NothingSent</span>),
<span class="ident">state</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="ident">EMPTY</span>),
}
}
<span class="kw">pub</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">unsafe</span> {
<span class="comment">// Sanity check</span>
<span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>() {
<span class="ident">NothingSent</span> <span class="op">=></span> {}
_ <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"sending on a oneshot that's already sent on "</span>),
}
<span class="macro">assert</span><span class="macro">!</span>((<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">is_none</span>());
<span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>(), <span class="prelude-val">Some</span>(<span class="ident">t</span>));
<span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>);
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DATA</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="comment">// Sent the data, no one was waiting</span>
<span class="ident">EMPTY</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(()),
<span class="comment">// Couldn't send the data, the port hung up first. Return the data</span>
<span class="comment">// back up the stack.</span>
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {
<span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">NothingSent</span>);
<span class="prelude-val">Err</span>((<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">take</span>().<span class="ident">unwrap</span>())
}
<span class="comment">// Not possible, these are one-use channels</span>
<span class="ident">DATA</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(),
<span class="comment">// There is a thread waiting on the other end. We leave the 'DATA'</span>
<span class="comment">// state inside so it'll pick it up on the other end.</span>
<span class="ident">ptr</span> <span class="op">=></span> {
<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>).<span class="ident">signal</span>();
<span class="prelude-val">Ok</span>(())
}
}
}
}
<span class="comment">// Just tests whether this channel has been sent on or not, this is only</span>
<span class="comment">// safe to use from the sender.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">sent</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="kw">unsafe</span> {
<span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>() {
<span class="ident">NothingSent</span> <span class="op">=></span> <span class="bool-val">false</span>,
_ <span class="op">=></span> <span class="bool-val">true</span>,
}
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">recv</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">deadline</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Instant</span><span class="op">></span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Failure</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="comment">// Attempt to not block the thread (it's a little expensive). If it looks</span>
<span class="comment">// like we're not empty, then immediately go through to `try_recv`.</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">==</span> <span class="ident">EMPTY</span> {
<span class="kw">let</span> (<span class="ident">wait_token</span>, <span class="ident">signal_token</span>) <span class="op">=</span> <span class="ident">blocking</span>::<span class="ident">tokens</span>();
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">signal_token</span>.<span class="ident">cast_to_usize</span>() };
<span class="comment">// race with senders to enter the blocking state</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">EMPTY</span>, <span class="ident">ptr</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">==</span> <span class="ident">EMPTY</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">deadline</span>) <span class="op">=</span> <span class="ident">deadline</span> {
<span class="kw">let</span> <span class="ident">timed_out</span> <span class="op">=</span> <span class="op">!</span><span class="ident">wait_token</span>.<span class="ident">wait_max_until</span>(<span class="ident">deadline</span>);
<span class="comment">// Try to reset the state</span>
<span class="kw">if</span> <span class="ident">timed_out</span> {
<span class="self">self</span>.<span class="ident">abort_selection</span>().<span class="ident">map_err</span>(<span class="ident">Upgraded</span>)<span class="question-mark">?</span>;
}
} <span class="kw">else</span> {
<span class="ident">wait_token</span>.<span class="ident">wait</span>();
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) <span class="op">!=</span> <span class="ident">EMPTY</span>);
}
} <span class="kw">else</span> {
<span class="comment">// drop the signal token, since we never blocked</span>
<span class="ident">drop</span>(<span class="kw">unsafe</span> { <span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>) });
}
}
<span class="self">self</span>.<span class="ident">try_recv</span>()
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">try_recv</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">Failure</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="kw">unsafe</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">EMPTY</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Empty</span>),
<span class="comment">// We saw some data on the channel, but the channel can be used</span>
<span class="comment">// again to send us an upgrade. As a result, we need to re-insert</span>
<span class="comment">// into the channel that there's no data available (otherwise we'll</span>
<span class="comment">// just see DATA next time). This is done as a cmpxchg because if</span>
<span class="comment">// the state changes under our feet we'd rather just see that state</span>
<span class="comment">// change.</span>
<span class="ident">DATA</span> <span class="op">=></span> {
<span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">DATA</span>, <span class="ident">EMPTY</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>);
<span class="kw">match</span> (<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</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="prelude-val">None</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(),
}
}
<span class="comment">// There's no guarantee that we receive before an upgrade happens,</span>
<span class="comment">// and an upgrade flags the channel as disconnected, so when we see</span>
<span class="comment">// this we first need to check if there's data available and *then*</span>
<span class="comment">// we go through and process the upgrade.</span>
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {
<span class="kw">match</span> (<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</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="prelude-val">None</span> <span class="op">=></span> {
<span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>) {
<span class="ident">SendUsed</span> <span class="op">|</span> <span class="ident">NothingSent</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Disconnected</span>),
<span class="ident">GoUp</span>(<span class="ident">upgrade</span>) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">Upgraded</span>(<span class="ident">upgrade</span>))
}
}
}
}
<span class="comment">// We are the sole receiver; there cannot be a blocking</span>
<span class="comment">// receiver already.</span>
_ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>()
}
}
}
<span class="comment">// Returns whether the upgrade was completed. If the upgrade wasn't</span>
<span class="comment">// completed, then the port couldn't get sent to the other half (it will</span>
<span class="comment">// never receive it).</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">upgrade</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">up</span>: <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) <span class="op">-></span> <span class="ident">UpgradeResult</span> {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>() {
<span class="ident">NothingSent</span> <span class="op">=></span> <span class="ident">NothingSent</span>,
<span class="ident">SendUsed</span> <span class="op">=></span> <span class="ident">SendUsed</span>,
_ <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"upgrading again"</span>),
};
<span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">GoUp</span>(<span class="ident">up</span>));
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="comment">// If the channel is empty or has data on it, then we're good to go.</span>
<span class="comment">// Senders will check the data before the upgrade (in case we</span>
<span class="comment">// plastered over the DATA state).</span>
<span class="ident">DATA</span> <span class="op">|</span> <span class="ident">EMPTY</span> <span class="op">=></span> <span class="ident">UpSuccess</span>,
<span class="comment">// If the other end is already disconnected, then we failed the</span>
<span class="comment">// upgrade. Be sure to trash the port we were given.</span>
<span class="ident">DISCONNECTED</span> <span class="op">=></span> { <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">prev</span>); <span class="ident">UpDisconnected</span> }
<span class="comment">// If someone's waiting, we gotta wake them up</span>
<span class="ident">ptr</span> <span class="op">=></span> <span class="ident">UpWoke</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>))
}
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">drop_chan</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">DATA</span> <span class="op">|</span> <span class="ident">DISCONNECTED</span> <span class="op">|</span> <span class="ident">EMPTY</span> <span class="op">=></span> {}
<span class="comment">// If someone's waiting, we gotta wake them up</span>
<span class="ident">ptr</span> <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>).<span class="ident">signal</span>();
}
}
}
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">drop_port</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="ident">DISCONNECTED</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="comment">// An empty channel has nothing to do, and a remotely disconnected</span>
<span class="comment">// channel also has nothing to do b/c we're about to run the drop</span>
<span class="comment">// glue</span>
<span class="ident">DISCONNECTED</span> <span class="op">|</span> <span class="ident">EMPTY</span> <span class="op">=></span> {}
<span class="comment">// There's data on the channel, so make sure we destroy it promptly.</span>
<span class="comment">// This is why not using an arc is a little difficult (need the box</span>
<span class="comment">// to stay valid while we take the data).</span>
<span class="ident">DATA</span> <span class="op">=></span> <span class="kw">unsafe</span> { (<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">take</span>().<span class="ident">unwrap</span>(); },
<span class="comment">// We're the only ones that can block on this port</span>
_ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>()
}
}
<span class="comment">////////////////////////////////////////////////////////////////////////////</span>
<span class="comment">// select implementation</span>
<span class="comment">////////////////////////////////////////////////////////////////////////////</span>
<span class="comment">// If Ok, the value is whether this port has data, if Err, then the upgraded</span>
<span class="comment">// port needs to be checked instead of this one.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">can_recv</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">bool</span>, <span class="ident">Receiver</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="kw">unsafe</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">EMPTY</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">false</span>), <span class="comment">// Welp, we tried</span>
<span class="ident">DATA</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>), <span class="comment">// we have some un-acquired data</span>
<span class="ident">DISCONNECTED</span> <span class="kw">if</span> (<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">is_some</span>() <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>), <span class="comment">// we have data</span>
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {
<span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>) {
<span class="comment">// The other end sent us an upgrade, so we need to</span>
<span class="comment">// propagate upwards whether the upgrade can receive</span>
<span class="comment">// data</span>
<span class="ident">GoUp</span>(<span class="ident">upgrade</span>) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">upgrade</span>),
<span class="comment">// If the other end disconnected without sending an</span>
<span class="comment">// upgrade, then we have data to receive (the channel is</span>
<span class="comment">// disconnected).</span>
<span class="ident">up</span> <span class="op">=></span> { <span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">up</span>); <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>) }
}
}
_ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(), <span class="comment">// we're the "one blocker"</span>
}
}
}
<span class="comment">// Attempts to start selection on this port. This can either succeed, fail</span>
<span class="comment">// because there is data, or fail because there is an upgrade pending.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">start_selection</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">token</span>: <span class="ident">SignalToken</span>) <span class="op">-></span> <span class="ident">SelectionResult</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">token</span>.<span class="ident">cast_to_usize</span>();
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">EMPTY</span>, <span class="ident">ptr</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="ident">EMPTY</span> <span class="op">=></span> <span class="ident">SelSuccess</span>,
<span class="ident">DATA</span> <span class="op">=></span> {
<span class="ident">drop</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>));
<span class="ident">SelCanceled</span>
}
<span class="ident">DISCONNECTED</span> <span class="kw">if</span> (<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">is_some</span>() <span class="op">=></span> {
<span class="ident">drop</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>));
<span class="ident">SelCanceled</span>
}
<span class="ident">DISCONNECTED</span> <span class="op">=></span> {
<span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>) {
<span class="comment">// The other end sent us an upgrade, so we need to</span>
<span class="comment">// propagate upwards whether the upgrade can receive</span>
<span class="comment">// data</span>
<span class="ident">GoUp</span>(<span class="ident">upgrade</span>) <span class="op">=></span> {
<span class="ident">SelUpgraded</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>), <span class="ident">upgrade</span>)
}
<span class="comment">// If the other end disconnected without sending an</span>
<span class="comment">// upgrade, then we have data to receive (the channel is</span>
<span class="comment">// disconnected).</span>
<span class="ident">up</span> <span class="op">=></span> {
<span class="ident">ptr</span>::<span class="ident">write</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">up</span>);
<span class="ident">drop</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>));
<span class="ident">SelCanceled</span>
}
}
}
_ <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(), <span class="comment">// we're the "one blocker"</span>
}
}
}
<span class="comment">// Remove a previous selecting thread from this port. This ensures that the</span>
<span class="comment">// blocked thread will no longer be visible to any other threads.</span>
<span class="comment">//</span>
<span class="comment">// The return value indicates whether there's data on this port.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">abort_selection</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">bool</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">state</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>) {
<span class="comment">// Each of these states means that no further activity will happen</span>
<span class="comment">// with regard to abortion selection</span>
<span class="ident">s</span> @ <span class="ident">EMPTY</span> <span class="op">|</span>
<span class="ident">s</span> @ <span class="ident">DATA</span> <span class="op">|</span>
<span class="ident">s</span> @ <span class="ident">DISCONNECTED</span> <span class="op">=></span> <span class="ident">s</span>,
<span class="comment">// If we've got a blocked thread, then use an atomic to gain ownership</span>
<span class="comment">// of it (may fail)</span>
<span class="ident">ptr</span> <span class="op">=></span> <span class="self">self</span>.<span class="ident">state</span>.<span class="ident">compare_and_swap</span>(<span class="ident">ptr</span>, <span class="ident">EMPTY</span>, <span class="ident">Ordering</span>::<span class="ident">SeqCst</span>)
};
<span class="comment">// Now that we've got ownership of our state, figure out what to do</span>
<span class="comment">// about it.</span>
<span class="kw">match</span> <span class="ident">state</span> {
<span class="ident">EMPTY</span> <span class="op">=></span> <span class="macro">unreachable</span><span class="macro">!</span>(),
<span class="comment">// our thread used for select was stolen</span>
<span class="ident">DATA</span> <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>),
<span class="comment">// If the other end has hung up, then we have complete ownership</span>
<span class="comment">// of the port. First, check if there was data waiting for us. This</span>
<span class="comment">// is possible if the other end sent something and then hung up.</span>
<span class="comment">//</span>
<span class="comment">// We then need to check to see if there was an upgrade requested,</span>
<span class="comment">// and if so, the upgraded port needs to have its selection aborted.</span>
<span class="ident">DISCONNECTED</span> <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="kw">if</span> (<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">data</span>.<span class="ident">get</span>()).<span class="ident">is_some</span>() {
<span class="prelude-val">Ok</span>(<span class="bool-val">true</span>)
} <span class="kw">else</span> {
<span class="kw">match</span> <span class="ident">ptr</span>::<span class="ident">replace</span>(<span class="self">self</span>.<span class="ident">upgrade</span>.<span class="ident">get</span>(), <span class="ident">SendUsed</span>) {
<span class="ident">GoUp</span>(<span class="ident">port</span>) <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">port</span>),
_ <span class="op">=></span> <span class="prelude-val">Ok</span>(<span class="bool-val">true</span>),
}
}
},
<span class="comment">// We woke ourselves up from select.</span>
<span class="ident">ptr</span> <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="ident">drop</span>(<span class="ident">SignalToken</span>::<span class="ident">cast_from_usize</span>(<span class="ident">ptr</span>));
<span class="prelude-val">Ok</span>(<span class="bool-val">false</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">Packet</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="macro">assert_eq</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">Ordering</span>::<span class="ident">SeqCst</span>), <span class="ident">DISCONNECTED</span>);
}
}
</pre>
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