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</pre><pre class="rust ">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">boxed</span>::<span class="ident">Box</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">UnsafeCell</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">mem</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ops</span>::{<span class="ident">Deref</span>, <span class="ident">DerefMut</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">AtomicUsize</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">Async</span>, <span class="ident">Future</span>, <span class="ident">Poll</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 type of futures-powered synchronization primitive which is a mutex between</span>
<span class="doccomment">/// two possible owners.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This primitive is not as generic as a full-blown mutex but is sufficient for</span>
<span class="doccomment">/// many use cases where there are only two possible owners of a resource. The</span>
<span class="doccomment">/// implementation of `BiLock` can be more optimized for just the two possible</span>
<span class="doccomment">/// owners.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that it's possible to use this lock through a poll-style interface with</span>
<span class="doccomment">/// the `poll_lock` method but you can also use it as a future with the `lock`</span>
<span class="doccomment">/// method that consumes a `BiLock` and returns a future that will resolve when</span>
<span class="doccomment">/// it's locked.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A `BiLock` is typically used for "split" operations where data which serves</span>
<span class="doccomment">/// two purposes wants to be split into two to be worked with separately. For</span>
<span class="doccomment">/// example a TCP stream could be both a reader and a writer or a framing layer</span>
<span class="doccomment">/// could be both a stream and a sink for messages. A `BiLock` enables splitting</span>
<span class="doccomment">/// these two and then using each independently in a futures-powered fashion.</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">BiLock</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="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="ident">state</span>: <span class="ident">AtomicUsize</span>,
<span class="ident">inner</span>: <span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Send</span><span class="op">></span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Send</span><span class="op">></span> <span class="ident">Sync</span> <span class="kw">for</span> <span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">BiLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Creates a new `BiLock` protecting the provided data.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Two handles to the lock are returned, and these are the only two handles</span>
<span class="doccomment">/// that will ever be available to the lock. These can then be sent to separate</span>
<span class="doccomment">/// tasks to be managed there.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">t</span>: <span class="ident">T</span>) <span class="op">-></span> (<span class="ident">BiLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">BiLock</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">state</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">0</span>),
<span class="ident">inner</span>: <span class="ident">UnsafeCell</span>::<span class="ident">new</span>(<span class="ident">t</span>),
});
(<span class="ident">BiLock</span> { <span class="ident">inner</span>: <span class="ident">inner</span>.<span class="ident">clone</span>() }, <span class="ident">BiLock</span> { <span class="ident">inner</span>: <span class="ident">inner</span> })
}
<span class="doccomment">/// Attempt to acquire this lock, returning `NotReady` if it can't be</span>
<span class="doccomment">/// acquired.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function will acquire the lock in a nonblocking fashion, returning</span>
<span class="doccomment">/// immediately if the lock is already held. If the lock is successfully</span>
<span class="doccomment">/// acquired then `Async::Ready` is returned with a value that represents</span>
<span class="doccomment">/// the locked value (and can be used to access the protected data). The</span>
<span class="doccomment">/// lock is unlocked when the returned `BiLockGuard` is dropped.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If the lock is already held then this function will return</span>
<span class="doccomment">/// `Async::NotReady`. In this case the current task will also be scheduled</span>
<span class="doccomment">/// to receive a notification when the lock would otherwise become</span>
<span class="doccomment">/// available.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function will panic if called outside the context of a future's</span>
<span class="doccomment">/// task.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">poll_lock</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">Async</span><span class="op"><</span><span class="ident">BiLockGuard</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>) {
<span class="comment">// Woohoo, we grabbed the lock!</span>
<span class="number">0</span> <span class="op">=></span> <span class="kw">return</span> <span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">BiLockGuard</span> { <span class="ident">inner</span>: <span class="self">self</span> }),
<span class="comment">// Oops, someone else has locked the lock</span>
<span class="number">1</span> <span class="op">=></span> {}
<span class="comment">// A task was previously blocked on this lock, likely our task,</span>
<span class="comment">// so we need to update that task.</span>
<span class="ident">n</span> <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="ident">drop</span>(<span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">n</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Task</span>));
}
}
<span class="kw">let</span> <span class="ident">me</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">task</span>::<span class="ident">current</span>());
<span class="kw">let</span> <span class="ident">me</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">me</span>) <span class="kw">as</span> <span class="ident">usize</span>;
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">compare_exchange</span>(<span class="number">1</span>, <span class="ident">me</span>, <span class="ident">SeqCst</span>, <span class="ident">SeqCst</span>) {
<span class="comment">// The lock is still locked, but we've now parked ourselves, so</span>
<span class="comment">// just report that we're scheduled to receive a notification.</span>
<span class="prelude-val">Ok</span>(_) <span class="op">=></span> <span class="kw">return</span> <span class="ident">Async</span>::<span class="ident">NotReady</span>,
<span class="comment">// Oops, looks like the lock was unlocked after our swap above</span>
<span class="comment">// and before the compare_exchange. Deallocate what we just</span>
<span class="comment">// allocated and go through the loop again.</span>
<span class="prelude-val">Err</span>(<span class="number">0</span>) <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="ident">drop</span>(<span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">me</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Task</span>));
},
<span class="comment">// The top of this loop set the previous state to 1, so if we</span>
<span class="comment">// failed the CAS above then it's because the previous value was</span>
<span class="comment">// *not* zero or one. This indicates that a task was blocked,</span>
<span class="comment">// but we're trying to acquire the lock and there's only one</span>
<span class="comment">// other reference of the lock, so it should be impossible for</span>
<span class="comment">// that task to ever block itself.</span>
<span class="prelude-val">Err</span>(<span class="ident">n</span>) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"invalid state: {}"</span>, <span class="ident">n</span>),
}
}
}
<span class="doccomment">/// Perform a "blocking lock" of this lock, consuming this lock handle and</span>
<span class="doccomment">/// returning a future to the acquired lock.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function consumes the `BiLock<T>` and returns a sentinel future,</span>
<span class="doccomment">/// `BiLockAcquire<T>`. The returned future will resolve to</span>
<span class="doccomment">/// `BiLockAcquired<T>` which represents a locked lock similarly to</span>
<span class="doccomment">/// `BiLockGuard<T>`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that the returned future will never resolve to an error.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">lock</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">BiLockAcquire</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">BiLockAcquire</span> {
<span class="ident">inner</span>: <span class="self">self</span>,
}
}
<span class="kw">fn</span> <span class="ident">unlock</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">swap</span>(<span class="number">0</span>, <span class="ident">SeqCst</span>) {
<span class="comment">// we've locked the lock, shouldn't be possible for us to see an</span>
<span class="comment">// unlocked lock.</span>
<span class="number">0</span> <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"invalid unlocked state"</span>),
<span class="comment">// Ok, no one else tried to get the lock, we're done.</span>
<span class="number">1</span> <span class="op">=></span> {}
<span class="comment">// Another task has parked themselves on this lock, let's wake them</span>
<span class="comment">// up as its now their turn.</span>
<span class="ident">n</span> <span class="op">=></span> <span class="kw">unsafe</span> {
<span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">n</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</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">Drop</span> <span class="kw">for</span> <span class="ident">Inner</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="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">SeqCst</span>), <span class="number">0</span>);
}
}
<span class="doccomment">/// Returned RAII guard from the `poll_lock` method.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This structure acts as a sentinel to the data in the `BiLock<T>` itself,</span>
<span class="doccomment">/// implementing `Deref` and `DerefMut` to `T`. When dropped, the lock will be</span>
<span class="doccomment">/// unlocked.</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">BiLockGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span>: <span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">inner</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">BiLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">BiLockGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</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="kw-2">&</span><span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">get</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">BiLockGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</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">inner</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">get</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">BiLockGuard</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">unlock</span>();
}
}
<span class="doccomment">/// Future returned by `BiLock::lock` which will resolve when the lock is</span>
<span class="doccomment">/// acquired.</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">BiLockAcquire</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">inner</span>: <span class="ident">BiLock</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">Future</span> <span class="kw">for</span> <span class="ident">BiLockAcquire</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">BiLockAcquired</span><span class="op"><</span><span class="ident">T</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="ident">BiLockAcquired</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, ()<span class="op">></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">poll_lock</span>() {
<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">r</span>) <span class="op">=></span> {
<span class="ident">mem</span>::<span class="ident">forget</span>(<span class="ident">r</span>);
<span class="prelude-val">Ok</span>(<span class="ident">BiLockAcquired</span> {
<span class="ident">inner</span>: <span class="ident">BiLock</span> { <span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">clone</span>() },
}.<span class="ident">into</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="doccomment">/// Resolved value of the `BiLockAcquire<T>` future.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This value, like `BiLockGuard<T>`, is a sentinel to the value `T` through</span>
<span class="doccomment">/// implementations of `Deref` and `DerefMut`. When dropped will unlock the</span>
<span class="doccomment">/// lock, and the original unlocked `BiLock<T>` can be recovered through the</span>
<span class="doccomment">/// `unlock` method.</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">BiLockAcquired</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">inner</span>: <span class="ident">BiLock</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">BiLockAcquired</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Recovers the original `BiLock<T>`, unlocking this lock.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">unlock</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">BiLock</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="comment">// note that unlocked is implemented in `Drop`, so we don't do anything</span>
<span class="comment">// here other than creating a new handle to return.</span>
<span class="ident">BiLock</span> { <span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">clone</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">BiLockAcquired</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">T</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="kw-2">&</span><span class="ident">T</span> {
<span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">get</span>() }
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">BiLockAcquired</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</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">inner</span>.<span class="ident">inner</span>.<span class="ident">inner</span>.<span class="ident">get</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">BiLockAcquired</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">unlock</span>();
}
}
</pre>
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