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<span class="doccomment">//! Reference counter for channels.</span>
<span class="kw">use</span> <span class="ident">std::isize</span>;
<span class="kw">use</span> <span class="ident">std::ops</span>;
<span class="kw">use</span> <span class="ident">std::process</span>;
<span class="kw">use</span> <span class="ident">std::sync::atomic</span>::{<span class="ident">AtomicBool</span>, <span class="ident">AtomicUsize</span>, <span class="ident">Ordering</span>};
<span class="doccomment">/// Reference counter internals.</span>
<span class="kw">struct</span> <span class="ident">Counter</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="doccomment">/// The number of senders associated with the channel.</span>
<span class="ident">senders</span>: <span class="ident">AtomicUsize</span>,
<span class="doccomment">/// The number of receivers associated with the channel.</span>
<span class="ident">receivers</span>: <span class="ident">AtomicUsize</span>,
<span class="doccomment">/// Set to `true` if the last sender or the last receiver reference deallocates the channel.</span>
<span class="ident">destroy</span>: <span class="ident">AtomicBool</span>,
<span class="doccomment">/// The internal channel.</span>
<span class="ident">chan</span>: <span class="ident">C</span>,
}
<span class="doccomment">/// Wraps a channel into the reference counter.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">new</span><span class="op"><</span><span class="ident">C</span><span class="op">></span>(<span class="ident">chan</span>: <span class="ident">C</span>) <span class="op">-</span><span class="op">></span> (<span class="ident">Sender</span><span class="op"><</span><span class="ident">C</span><span class="op">></span>, <span class="ident">Receiver</span><span class="op"><</span><span class="ident">C</span><span class="op">></span>) {
<span class="kw">let</span> <span class="ident">counter</span> <span class="op">=</span> <span class="ident">Box::into_raw</span>(<span class="ident">Box::new</span>(<span class="ident">Counter</span> {
<span class="ident">senders</span>: <span class="ident">AtomicUsize::new</span>(<span class="number">1</span>),
<span class="ident">receivers</span>: <span class="ident">AtomicUsize::new</span>(<span class="number">1</span>),
<span class="ident">destroy</span>: <span class="ident">AtomicBool::new</span>(<span class="bool-val">false</span>),
<span class="ident">chan</span>,
}));
<span class="kw">let</span> <span class="ident">s</span> <span class="op">=</span> <span class="ident">Sender</span> { <span class="ident">counter</span> };
<span class="kw">let</span> <span class="ident">r</span> <span class="op">=</span> <span class="ident">Receiver</span> { <span class="ident">counter</span> };
(<span class="ident">s</span>, <span class="ident">r</span>)
}
<span class="doccomment">/// The sending side.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct</span> <span class="ident">Sender</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="ident">counter</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Counter</span><span class="op"><</span><span class="ident">C</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> <span class="ident">Sender</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="doccomment">/// Returns the internal `Counter`.</span>
<span class="kw">fn</span> <span class="ident">counter</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">Counter</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">counter</span> }
}
<span class="doccomment">/// Acquires another sender reference.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">acquire</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">Sender</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">senders</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">Ordering::Relaxed</span>);
<span class="comment">// Cloning senders and calling `mem::forget` on the clones could potentially overflow the</span>
<span class="comment">// counter. It's very difficult to recover sensibly from such degenerate scenarios so we</span>
<span class="comment">// just abort when the count becomes very large.</span>
<span class="kw">if</span> <span class="ident">count</span> <span class="op">></span> <span class="ident">isize::MAX</span> <span class="kw">as</span> <span class="ident">usize</span> {
<span class="ident">process::abort</span>();
}
<span class="ident">Sender</span> {
<span class="ident">counter</span>: <span class="self">self</span>.<span class="ident">counter</span>,
}
}
<span class="doccomment">/// Releases the sender reference.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Function `disconnect` will be called if this is the last sender reference.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">release</span><span class="op"><</span><span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="ident">C</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">disconnect</span>: <span class="ident">F</span>) {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">senders</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span>, <span class="ident">Ordering::AcqRel</span>) <span class="op">=</span><span class="op">=</span> <span class="number">1</span> {
<span class="ident">disconnect</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">chan</span>);
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">destroy</span>.<span class="ident">swap</span>(<span class="bool-val">true</span>, <span class="ident">Ordering::AcqRel</span>) {
<span class="ident">drop</span>(<span class="ident">Box::from_raw</span>(<span class="self">self</span>.<span class="ident">counter</span>));
}
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> <span class="ident">ops::Deref</span> <span class="kw">for</span> <span class="ident">Sender</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">C</span>;
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">C</span> {
<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">chan</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> <span class="ident">PartialEq</span> <span class="kw">for</span> <span class="ident">Sender</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Sender</span><span class="op"><</span><span class="ident">C</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="self">self</span>.<span class="ident">counter</span> <span class="op">=</span><span class="op">=</span> <span class="ident">other</span>.<span class="ident">counter</span>
}
}
<span class="doccomment">/// The receiving side.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct</span> <span class="ident">Receiver</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="ident">counter</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Counter</span><span class="op"><</span><span class="ident">C</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> <span class="ident">Receiver</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="doccomment">/// Returns the internal `Counter`.</span>
<span class="kw">fn</span> <span class="ident">counter</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">Counter</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">counter</span> }
}
<span class="doccomment">/// Acquires another receiver reference.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn</span> <span class="ident">acquire</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">Receiver</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">count</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">receivers</span>.<span class="ident">fetch_add</span>(<span class="number">1</span>, <span class="ident">Ordering::Relaxed</span>);
<span class="comment">// Cloning receivers and calling `mem::forget` on the clones could potentially overflow the</span>
<span class="comment">// counter. It's very difficult to recover sensibly from such degenerate scenarios so we</span>
<span class="comment">// just abort when the count becomes very large.</span>
<span class="kw">if</span> <span class="ident">count</span> <span class="op">></span> <span class="ident">isize::MAX</span> <span class="kw">as</span> <span class="ident">usize</span> {
<span class="ident">process::abort</span>();
}
<span class="ident">Receiver</span> {
<span class="ident">counter</span>: <span class="self">self</span>.<span class="ident">counter</span>,
}
}
<span class="doccomment">/// Releases the receiver reference.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Function `disconnect` will be called if this is the last receiver reference.</span>
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">release</span><span class="op"><</span><span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="ident">C</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">disconnect</span>: <span class="ident">F</span>) {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">receivers</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span>, <span class="ident">Ordering::AcqRel</span>) <span class="op">=</span><span class="op">=</span> <span class="number">1</span> {
<span class="ident">disconnect</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">chan</span>);
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">destroy</span>.<span class="ident">swap</span>(<span class="bool-val">true</span>, <span class="ident">Ordering::AcqRel</span>) {
<span class="ident">drop</span>(<span class="ident">Box::from_raw</span>(<span class="self">self</span>.<span class="ident">counter</span>));
}
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> <span class="ident">ops::Deref</span> <span class="kw">for</span> <span class="ident">Receiver</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">C</span>;
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="ident">C</span> {
<span class="kw-2">&</span><span class="self">self</span>.<span class="ident">counter</span>().<span class="ident">chan</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> <span class="ident">PartialEq</span> <span class="kw">for</span> <span class="ident">Receiver</span><span class="op"><</span><span class="ident">C</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">eq</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">other</span>: <span class="kw-2">&</span><span class="ident">Receiver</span><span class="op"><</span><span class="ident">C</span><span class="op">></span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="self">self</span>.<span class="ident">counter</span> <span class="op">=</span><span class="op">=</span> <span class="ident">other</span>.<span class="ident">counter</span>
}
}
</pre></div>
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