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</pre><pre class="rust ">
<span class="doccomment">//! A multi-producer, single-consumer, futures-aware, FIFO queue with back pressure.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! A channel can be used as a communication primitive between tasks running on</span>
<span class="doccomment">//! `futures-rs` executors. Channel creation provides `Receiver` and `Sender`</span>
<span class="doccomment">//! handles. `Receiver` implements `Stream` and allows a task to read values</span>
<span class="doccomment">//! out of the channel. If there is no message to read from the channel, the</span>
<span class="doccomment">//! current task will be notified when a new value is sent. `Sender` implements</span>
<span class="doccomment">//! the `Sink` trait and allows a task to send messages into the channel. If</span>
<span class="doccomment">//! the channel is at capacity, then send will be rejected and the task will be</span>
<span class="doccomment">//! notified when additional capacity is available.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Disconnection</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! When all `Sender` handles have been dropped, it is no longer possible to</span>
<span class="doccomment">//! send values into the channel. This is considered the termination event of</span>
<span class="doccomment">//! the stream. As such, `Sender::poll` will return `Ok(Ready(None))`.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! If the receiver handle is dropped, then messages can no longer be read out</span>
<span class="doccomment">//! of the channel. In this case, a `send` will result in an error.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Clean Shutdown</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! If the `Receiver` is simply dropped, then it is possible for there to be</span>
<span class="doccomment">//! messages still in the channel that will not be processed. As such, it is</span>
<span class="doccomment">//! usually desirable to perform a "clean" shutdown. To do this, the receiver</span>
<span class="doccomment">//! will first call `close`, which will prevent any further messages to be sent</span>
<span class="doccomment">//! into the channel. Then, the receiver consumes the channel to completion, at</span>
<span class="doccomment">//! which point the receiver can be dropped.</span>
<span class="comment">// At the core, the channel uses an atomic FIFO queue for message passing. This</span>
<span class="comment">// queue is used as the primary coordination primitive. In order to enforce</span>
<span class="comment">// capacity limits and handle back pressure, a secondary FIFO queue is used to</span>
<span class="comment">// send parked task handles.</span>
<span class="comment">//</span>
<span class="comment">// The general idea is that the channel is created with a `buffer` size of `n`.</span>
<span class="comment">// The channel capacity is `n + num-senders`. Each sender gets one "guaranteed"</span>
<span class="comment">// slot to hold a message. This allows `Sender` to know for a fact that a send</span>
<span class="comment">// will succeed *before* starting to do the actual work of sending the value.</span>
<span class="comment">// Since most of this work is lock-free, once the work starts, it is impossible</span>
<span class="comment">// to safely revert.</span>
<span class="comment">//</span>
<span class="comment">// If the sender is unable to process a send operation, then the the curren</span>
<span class="comment">// task is parked and the handle is sent on the parked task queue.</span>
<span class="comment">//</span>
<span class="comment">// Note that the implementation guarantees that the channel capacity will never</span>
<span class="comment">// exceed the configured limit, however there is no *strict* guarantee that the</span>
<span class="comment">// receiver will wake up a parked task *immediately* when a slot becomes</span>
<span class="comment">// available. However, it will almost always unpark a task when a slot becomes</span>
<span class="comment">// available and it is *guaranteed* that a sender will be unparked when the</span>
<span class="comment">// message that caused the sender to become parked is read out of the channel.</span>
<span class="comment">//</span>
<span class="comment">// The steps for sending a message are roughly:</span>
<span class="comment">//</span>
<span class="comment">// 1) Increment the channel message count</span>
<span class="comment">// 2) If the channel is at capacity, push the task handle onto the wait queue</span>
<span class="comment">// 3) Push the message onto the message queue.</span>
<span class="comment">//</span>
<span class="comment">// The steps for receiving a message are roughly:</span>
<span class="comment">//</span>
<span class="comment">// 1) Pop a message from the message queue</span>
<span class="comment">// 2) Pop a task handle from the wait queue</span>
<span class="comment">// 3) Decrement the channel message count.</span>
<span class="comment">//</span>
<span class="comment">// It's important for the order of operations on lock-free structures to happen</span>
<span class="comment">// in reverse order between the sender and receiver. This makes the message</span>
<span class="comment">// queue the primary coordination structure and establishes the necessary</span>
<span class="comment">// happens-before semantics required for the acquire / release semantics used</span>
<span class="comment">// by the queue structure.</span>
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</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">any</span>::<span class="ident">Any</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">std</span>::<span class="ident">sync</span>::{<span class="ident">Arc</span>, <span class="ident">Mutex</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">thread</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">usize</span>;
<span class="kw">use</span> <span class="ident">sync</span>::<span class="ident">mpsc</span>::<span class="ident">queue</span>::{<span class="ident">Queue</span>, <span class="ident">PopResult</span>};
<span class="kw">use</span> <span class="ident">task</span>::{<span class="self">self</span>, <span class="ident">Task</span>};
<span class="kw">use</span> {<span class="ident">Async</span>, <span class="ident">AsyncSink</span>, <span class="ident">Poll</span>, <span class="ident">StartSend</span>, <span class="ident">Sink</span>, <span class="ident">Stream</span>};
<span class="kw">mod</span> <span class="ident">queue</span>;
<span class="doccomment">/// The transmission end of a channel which is used to send values.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is created by the `channel` 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">Sender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="comment">// Channel state shared between the sender and receiver.</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="comment">// Handle to the task that is blocked on this sender. This handle is sent</span>
<span class="comment">// to the receiver half in order to be notified when the sender becomes</span>
<span class="comment">// unblocked.</span>
<span class="ident">sender_task</span>: <span class="ident">SenderTask</span>,
<span class="comment">// True if the sender might be blocked. This is an optimization to avoid</span>
<span class="comment">// having to lock the mutex most of the time.</span>
<span class="ident">maybe_parked</span>: <span class="ident">bool</span>,
}
<span class="doccomment">/// The transmission end of a channel which is used to send values.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is created by the `unbounded` 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">UnboundedSender</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="kw">fn</span> <span class="ident">_assert_kinds</span>() {
<span class="kw">fn</span> <span class="ident">_assert_send</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Send</span><span class="op">></span>() {}
<span class="kw">fn</span> <span class="ident">_assert_sync</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Sync</span><span class="op">></span>() {}
<span class="kw">fn</span> <span class="ident">_assert_clone</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Clone</span><span class="op">></span>() {}
<span class="ident">_assert_send</span>::<span class="op"><</span><span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">u32</span><span class="op">>></span>();
<span class="ident">_assert_sync</span>::<span class="op"><</span><span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">u32</span><span class="op">>></span>();
<span class="ident">_assert_clone</span>::<span class="op"><</span><span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">u32</span><span class="op">>></span>();
}
<span class="doccomment">/// The receiving end of a channel which implements the `Stream` trait.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is a concrete implementation of a stream which can be used to represent</span>
<span class="doccomment">/// a stream of values being computed elsewhere. This is created by the</span>
<span class="doccomment">/// `channel` 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">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">/// The receiving end of a channel which implements the `Stream` trait.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is a concrete implementation of a stream which can be used to represent</span>
<span class="doccomment">/// a stream of values being computed elsewhere. This is created by the</span>
<span class="doccomment">/// `unbounded` 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">UnboundedReceiver</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">/// Error type for sending, used when the receiving end of a channel is</span>
<span class="doccomment">/// dropped</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">T</span>);
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Debug</span> <span class="kw">for</span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">fmt</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="ident">fmt</span>.<span class="ident">debug_tuple</span>(<span class="string">"SendError"</span>)
.<span class="ident">field</span>(<span class="kw-2">&</span><span class="string">"..."</span>)
.<span class="ident">finish</span>()
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">fmt</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="macro">write</span><span class="macro">!</span>(<span class="ident">fmt</span>, <span class="string">"send failed because receiver is gone"</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Any</span><span class="op">></span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></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">"send failed because receiver is gone"</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Returns the message that was attempted to be sent but failed.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">into_inner</span>(<span class="self">self</span>) <span class="op">-></span> <span class="ident">T</span> {
<span class="self">self</span>.<span class="number">0</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="comment">// Max buffer size of the channel. If `None` then the channel is unbounded.</span>
<span class="ident">buffer</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</span><span class="op">></span>,
<span class="comment">// Internal channel state. Consists of the number of messages stored in the</span>
<span class="comment">// channel as well as a flag signalling that the channel is closed.</span>
<span class="ident">state</span>: <span class="ident">AtomicUsize</span>,
<span class="comment">// Atomic, FIFO queue used to send messages to the receiver</span>
<span class="ident">message_queue</span>: <span class="ident">Queue</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">// Atomic, FIFO queue used to send parked task handles to the receiver.</span>
<span class="ident">parked_queue</span>: <span class="ident">Queue</span><span class="op"><</span><span class="ident">SenderTask</span><span class="op">></span>,
<span class="comment">// Number of senders in existence</span>
<span class="ident">num_senders</span>: <span class="ident">AtomicUsize</span>,
<span class="comment">// Handle to the receiver's task.</span>
<span class="ident">recv_task</span>: <span class="ident">Mutex</span><span class="op"><</span><span class="ident">ReceiverTask</span><span class="op">></span>,
}
<span class="comment">// Struct representation of `Inner::state`.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>, <span class="ident">Clone</span>, <span class="ident">Copy</span>)]</span>
<span class="kw">struct</span> <span class="ident">State</span> {
<span class="comment">// `true` when the channel is open</span>
<span class="ident">is_open</span>: <span class="ident">bool</span>,
<span class="comment">// Number of messages in the channel</span>
<span class="ident">num_messages</span>: <span class="ident">usize</span>,
}
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">ReceiverTask</span> {
<span class="ident">unparked</span>: <span class="ident">bool</span>,
<span class="ident">task</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">Task</span><span class="op">></span>,
}
<span class="comment">// Returned from Receiver::try_park()</span>
<span class="kw">enum</span> <span class="ident">TryPark</span> {
<span class="ident">Parked</span>,
<span class="ident">Closed</span>,
<span class="ident">NotEmpty</span>,
}
<span class="comment">// The `is_open` flag is stored in the left-most bit of `Inner::state`</span>
<span class="kw">const</span> <span class="ident">OPEN_MASK</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="number">1</span> <span class="op"><<</span> <span class="number">31</span>;
<span class="comment">// When a new channel is created, it is created in the open state with no</span>
<span class="comment">// pending messages.</span>
<span class="kw">const</span> <span class="ident">INIT_STATE</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="ident">OPEN_MASK</span>;
<span class="comment">// The maximum number of messages that a channel can track is `usize::MAX > 1`</span>
<span class="kw">const</span> <span class="ident">MAX_CAPACITY</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="op">!</span>(<span class="ident">OPEN_MASK</span>);
<span class="comment">// The maximum requested buffer size must be less than the maximum capacity of</span>
<span class="comment">// a channel. This is because each sender gets a guaranteed slot.</span>
<span class="kw">const</span> <span class="ident">MAX_BUFFER</span>: <span class="ident">usize</span> <span class="op">=</span> <span class="ident">MAX_CAPACITY</span> <span class="op">>></span> <span class="number">1</span>;
<span class="comment">// Sent to the consumer to wake up blocked producers</span>
<span class="kw">type</span> <span class="ident">SenderTask</span> <span class="op">=</span> <span class="ident">Arc</span><span class="op"><</span><span class="ident">Mutex</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="op">></span>;
<span class="doccomment">/// Creates an in-memory channel implementation of the `Stream` trait with</span>
<span class="doccomment">/// bounded capacity.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method creates a concrete implementation of the `Stream` trait which</span>
<span class="doccomment">/// can be used to send values across threads in a streaming fashion. This</span>
<span class="doccomment">/// channel is unique in that it implements back pressure to ensure that the</span>
<span class="doccomment">/// sender never outpaces the receiver. The channel capacity is equal to</span>
<span class="doccomment">/// `buffer + num-senders`. In other words, each sender gets a guaranteed slot</span>
<span class="doccomment">/// in the channel capacity, and on top of that there are `buffer` "first come,</span>
<span class="doccomment">/// first serve" slots available to all senders.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `Receiver` returned implements the `Stream` trait and has access to any</span>
<span class="doccomment">/// number of the associated combinators for transforming the result.</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="ident">buffer</span>: <span class="ident">usize</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="comment">// Check that the requested buffer size does not exceed the maximum buffer</span>
<span class="comment">// size permitted by the system.</span>
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">buffer</span> <span class="op"><</span> <span class="ident">MAX_BUFFER</span>, <span class="string">"requested buffer size too large"</span>);
<span class="ident">channel2</span>(<span class="prelude-val">Some</span>(<span class="ident">buffer</span>))
}
<span class="doccomment">/// Creates an in-memory channel implementation of the `Stream` trait with</span>
<span class="doccomment">/// unbounded capacity.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This method creates a concrete implementation of the `Stream` trait which</span>
<span class="doccomment">/// can be used to send values across threads in a streaming fashion. A `send`</span>
<span class="doccomment">/// on this channel will always succeed as long as the receive half has not</span>
<span class="doccomment">/// been closed. If the receiver falls behind, messages will be buffered</span>
<span class="doccomment">/// internally.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// **Note** that the amount of available system memory is an implicit bound to</span>
<span class="doccomment">/// the channel. Using an `unbounded` channel has the ability of causing the</span>
<span class="doccomment">/// process to run out of memory. In this case, the process will be aborted.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">unbounded</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">-></span> (<span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">UnboundedReceiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) {
<span class="kw">let</span> (<span class="ident">tx</span>, <span class="ident">rx</span>) <span class="op">=</span> <span class="ident">channel2</span>(<span class="prelude-val">None</span>);
(<span class="ident">UnboundedSender</span>(<span class="ident">tx</span>), <span class="ident">UnboundedReceiver</span>(<span class="ident">rx</span>))
}
<span class="kw">fn</span> <span class="ident">channel2</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">buffer</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">usize</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">buffer</span>: <span class="ident">buffer</span>,
<span class="ident">state</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="ident">INIT_STATE</span>),
<span class="ident">message_queue</span>: <span class="ident">Queue</span>::<span class="ident">new</span>(),
<span class="ident">parked_queue</span>: <span class="ident">Queue</span>::<span class="ident">new</span>(),
<span class="ident">num_senders</span>: <span class="ident">AtomicUsize</span>::<span class="ident">new</span>(<span class="number">1</span>),
<span class="ident">recv_task</span>: <span class="ident">Mutex</span>::<span class="ident">new</span>(<span class="ident">ReceiverTask</span> {
<span class="ident">unparked</span>: <span class="bool-val">false</span>,
<span class="ident">task</span>: <span class="prelude-val">None</span>,
}),
});
<span class="kw">let</span> <span class="ident">tx</span> <span class="op">=</span> <span class="ident">Sender</span> {
<span class="ident">inner</span>: <span class="ident">inner</span>.<span class="ident">clone</span>(),
<span class="ident">sender_task</span>: <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Mutex</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>)),
<span class="ident">maybe_parked</span>: <span class="bool-val">false</span>,
};
<span class="kw">let</span> <span class="ident">rx</span> <span class="op">=</span> <span class="ident">Receiver</span> {
<span class="ident">inner</span>: <span class="ident">inner</span>,
};
(<span class="ident">tx</span>, <span class="ident">rx</span>)
}
<span class="comment">/*
*
* ===== impl Sender =====
*
*/</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="comment">// Do the send without failing</span>
<span class="kw">fn</span> <span class="ident">do_send</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">msg</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">can_park</span>: <span class="ident">bool</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="comment">// First, increment the number of messages contained by the channel.</span>
<span class="comment">// This operation will also atomically determine if the sender task</span>
<span class="comment">// should be parked.</span>
<span class="comment">//</span>
<span class="comment">// None is returned in the case that the channel has been closed by the</span>
<span class="comment">// receiver. This happens when `Receiver::close` is called or the</span>
<span class="comment">// receiver is dropped.</span>
<span class="kw">let</span> <span class="ident">park_self</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">inc_num_messages</span>(<span class="ident">msg</span>.<span class="ident">is_none</span>()) {
<span class="prelude-val">Some</span>(<span class="ident">park_self</span>) <span class="op">=></span> <span class="ident">park_self</span>,
<span class="prelude-val">None</span> <span class="op">=></span> {
<span class="comment">// The receiver has closed the channel. Only abort if actually</span>
<span class="comment">// sending a message. It is important that the stream</span>
<span class="comment">// termination (None) is always sent. This technically means</span>
<span class="comment">// that it is possible for the queue to contain the following</span>
<span class="comment">// number of messages:</span>
<span class="comment">//</span>
<span class="comment">// num-senders + buffer + 1</span>
<span class="comment">//</span>
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Some</span>(<span class="ident">msg</span>) <span class="op">=</span> <span class="ident">msg</span> {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">SendError</span>(<span class="ident">msg</span>));
} <span class="kw">else</span> {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(());
}
}
};
<span class="comment">// If the channel has reached capacity, then the sender task needs to</span>
<span class="comment">// be parked. This will send the task handle on the parked task queue.</span>
<span class="comment">//</span>
<span class="comment">// However, when `do_send` is called while dropping the `Sender`,</span>
<span class="comment">// `task::current()` can't be called safely. In this case, in order to</span>
<span class="comment">// maintain internal consistency, a blank message is pushed onto the</span>
<span class="comment">// parked task queue.</span>
<span class="kw">if</span> <span class="ident">park_self</span> {
<span class="self">self</span>.<span class="ident">park</span>(<span class="ident">can_park</span>);
}
<span class="self">self</span>.<span class="ident">queue_push_and_signal</span>(<span class="ident">msg</span>);
<span class="prelude-val">Ok</span>(())
}
<span class="comment">// Do the send without parking current task.</span>
<span class="comment">//</span>
<span class="comment">// To be called from unbounded sender.</span>
<span class="kw">fn</span> <span class="ident">do_send_nb</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">msg</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">inc_num_messages</span>(<span class="bool-val">false</span>) {
<span class="prelude-val">Some</span>(<span class="ident">park_self</span>) <span class="op">=></span> <span class="macro">assert</span><span class="macro">!</span>(<span class="op">!</span><span class="ident">park_self</span>),
<span class="prelude-val">None</span> <span class="op">=></span> <span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">SendError</span>(<span class="ident">msg</span>)),
};
<span class="self">self</span>.<span class="ident">queue_push_and_signal</span>(<span class="prelude-val">Some</span>(<span class="ident">msg</span>));
<span class="prelude-val">Ok</span>(())
}
<span class="comment">// Push message to the queue and signal to the receiver</span>
<span class="kw">fn</span> <span class="ident">queue_push_and_signal</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">msg</span>: <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>) {
<span class="comment">// Push the message onto the message queue</span>
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">message_queue</span>.<span class="ident">push</span>(<span class="ident">msg</span>);
<span class="comment">// Signal to the receiver that a message has been enqueued. If the</span>
<span class="comment">// receiver is parked, this will unpark the task.</span>
<span class="self">self</span>.<span class="ident">signal</span>();
}
<span class="comment">// Increment the number of queued messages. Returns if the sender should</span>
<span class="comment">// block.</span>
<span class="kw">fn</span> <span class="ident">inc_num_messages</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">close</span>: <span class="ident">bool</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">bool</span><span class="op">></span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">curr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>);
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">decode_state</span>(<span class="ident">curr</span>);
<span class="comment">// The receiver end closed the channel.</span>
<span class="kw">if</span> <span class="op">!</span><span class="ident">state</span>.<span class="ident">is_open</span> {
<span class="kw">return</span> <span class="prelude-val">None</span>;
}
<span class="comment">// This probably is never hit? Odds are the process will run out of</span>
<span class="comment">// memory first. It may be worth to return something else in this</span>
<span class="comment">// case?</span>
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">state</span>.<span class="ident">num_messages</span> <span class="op"><</span> <span class="ident">MAX_CAPACITY</span>, <span class="string">"buffer space exhausted; \
sending this messages would overflow the state"</span>);
<span class="ident">state</span>.<span class="ident">num_messages</span> <span class="op">+=</span> <span class="number">1</span>;
<span class="comment">// The channel is closed by all sender handles being dropped.</span>
<span class="kw">if</span> <span class="ident">close</span> {
<span class="ident">state</span>.<span class="ident">is_open</span> <span class="op">=</span> <span class="bool-val">false</span>;
}
<span class="kw">let</span> <span class="ident">next</span> <span class="op">=</span> <span class="ident">encode_state</span>(<span class="kw-2">&</span><span class="ident">state</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="ident">curr</span>, <span class="ident">next</span>, <span class="ident">SeqCst</span>, <span class="ident">SeqCst</span>) {
<span class="prelude-val">Ok</span>(_) <span class="op">=></span> {
<span class="comment">// Block if the current number of pending messages has exceeded</span>
<span class="comment">// the configured buffer size</span>
<span class="kw">let</span> <span class="ident">park_self</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">buffer</span> {
<span class="prelude-val">Some</span>(<span class="ident">buffer</span>) <span class="op">=></span> <span class="ident">state</span>.<span class="ident">num_messages</span> <span class="op">></span> <span class="ident">buffer</span>,
<span class="prelude-val">None</span> <span class="op">=></span> <span class="bool-val">false</span>,
};
<span class="kw">return</span> <span class="prelude-val">Some</span>(<span class="ident">park_self</span>)
}
<span class="prelude-val">Err</span>(<span class="ident">actual</span>) <span class="op">=></span> <span class="ident">curr</span> <span class="op">=</span> <span class="ident">actual</span>,
}
}
}
<span class="comment">// Signal to the receiver task that a message has been enqueued</span>
<span class="kw">fn</span> <span class="ident">signal</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="comment">// TODO</span>
<span class="comment">// This logic can probably be improved by guarding the lock with an</span>
<span class="comment">// atomic.</span>
<span class="comment">//</span>
<span class="comment">// Do this step first so that the lock is dropped when</span>
<span class="comment">// `unpark` is called</span>
<span class="kw">let</span> <span class="ident">task</span> <span class="op">=</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">recv_task</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">recv_task</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="comment">// If the receiver has already been unparked, then there is nothing</span>
<span class="comment">// more to do</span>
<span class="kw">if</span> <span class="ident">recv_task</span>.<span class="ident">unparked</span> {
<span class="kw">return</span>;
}
<span class="comment">// Setting this flag enables the receiving end to detect that</span>
<span class="comment">// an unpark event happened in order to avoid unecessarily</span>
<span class="comment">// parking.</span>
<span class="ident">recv_task</span>.<span class="ident">unparked</span> <span class="op">=</span> <span class="bool-val">true</span>;
<span class="ident">recv_task</span>.<span class="ident">task</span>.<span class="ident">take</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">task</span> {
<span class="ident">task</span>.<span class="ident">notify</span>();
}
}
<span class="kw">fn</span> <span class="ident">park</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">can_park</span>: <span class="ident">bool</span>) {
<span class="comment">// TODO: clean up internal state if the task::current will fail</span>
<span class="kw">let</span> <span class="ident">task</span> <span class="op">=</span> <span class="kw">if</span> <span class="ident">can_park</span> {
<span class="prelude-val">Some</span>(<span class="ident">task</span>::<span class="ident">current</span>())
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
};
<span class="kw-2">*</span><span class="self">self</span>.<span class="ident">sender_task</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>() <span class="op">=</span> <span class="ident">task</span>;
<span class="comment">// Send handle over queue</span>
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">sender_task</span>.<span class="ident">clone</span>();
<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">parked_queue</span>.<span class="ident">push</span>(<span class="ident">t</span>);
<span class="comment">// Check to make sure we weren't closed after we sent our task on the</span>
<span class="comment">// queue</span>
<span class="kw">let</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">decode_state</span>(<span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>));
<span class="self">self</span>.<span class="ident">maybe_parked</span> <span class="op">=</span> <span class="ident">state</span>.<span class="ident">is_open</span>;
}
<span class="kw">fn</span> <span class="ident">poll_unparked</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Async</span><span class="op"><</span>()<span class="op">></span> {
<span class="comment">// First check the `maybe_parked` variable. This avoids acquiring the</span>
<span class="comment">// lock in most cases</span>
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">maybe_parked</span> {
<span class="comment">// Get a lock on the task handle</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">task</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">sender_task</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw">if</span> <span class="ident">task</span>.<span class="ident">is_none</span>() {
<span class="self">self</span>.<span class="ident">maybe_parked</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="kw">return</span> <span class="ident">Async</span>::<span class="ident">Ready</span>(())
}
<span class="comment">// At this point, an unpark request is pending, so there will be an</span>
<span class="comment">// unpark sometime in the future. We just need to make sure that</span>
<span class="comment">// the correct task will be notified.</span>
<span class="comment">//</span>
<span class="comment">// Update the task in case the `Sender` has been moved to another</span>
<span class="comment">// task</span>
<span class="kw-2">*</span><span class="ident">task</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">task</span>::<span class="ident">current</span>());
<span class="ident">Async</span>::<span class="ident">NotReady</span>
} <span class="kw">else</span> {
<span class="ident">Async</span>::<span class="ident">Ready</span>(())
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Sink</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">type</span> <span class="ident">SinkItem</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">type</span> <span class="ident">SinkError</span> <span class="op">=</span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>;
<span class="kw">fn</span> <span class="ident">start_send</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">msg</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">StartSend</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="comment">// If the sender is currently blocked, reject the message before doing</span>
<span class="comment">// any work.</span>
<span class="kw">if</span> <span class="op">!</span><span class="self">self</span>.<span class="ident">poll_unparked</span>().<span class="ident">is_ready</span>() {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">AsyncSink</span>::<span class="ident">NotReady</span>(<span class="ident">msg</span>));
}
<span class="comment">// The channel has capacity to accept the message, so send it.</span>
<span class="macro">try</span><span class="macro">!</span>(<span class="self">self</span>.<span class="ident">do_send</span>(<span class="prelude-val">Some</span>(<span class="ident">msg</span>), <span class="bool-val">true</span>));
<span class="prelude-val">Ok</span>(<span class="ident">AsyncSink</span>::<span class="ident">Ready</span>)
}
<span class="kw">fn</span> <span class="ident">poll_complete</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">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</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="op">-></span> <span class="ident">Poll</span><span class="op"><</span>(), <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(()))
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Sends the provided message along this channel.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is an unbounded sender, so this function differs from `Sink::send`</span>
<span class="doccomment">/// by ensuring the return type reflects that the channel is always ready to</span>
<span class="doccomment">/// receive messages.</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">msg</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">do_send_nb</span>(<span class="ident">msg</span>)
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Sink</span> <span class="kw">for</span> <span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">SinkItem</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">type</span> <span class="ident">SinkError</span> <span class="op">=</span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>;
<span class="kw">fn</span> <span class="ident">start_send</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">msg</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">StartSend</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">start_send</span>(<span class="ident">msg</span>)
}
<span class="kw">fn</span> <span class="ident">poll_complete</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">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">poll_complete</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="op">-></span> <span class="ident">Poll</span><span class="op"><</span>(), <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</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">Sink</span> <span class="kw">for</span> <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">SinkItem</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">type</span> <span class="ident">SinkError</span> <span class="op">=</span> <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>;
<span class="kw">fn</span> <span class="ident">start_send</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">msg</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="ident">StartSend</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="macro">try</span><span class="macro">!</span>(<span class="self">self</span>.<span class="number">0</span>.<span class="ident">do_send_nb</span>(<span class="ident">msg</span>));
<span class="prelude-val">Ok</span>(<span class="ident">AsyncSink</span>::<span class="ident">Ready</span>)
}
<span class="kw">fn</span> <span class="ident">poll_complete</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">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</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="op">-></span> <span class="ident">Poll</span><span class="op"><</span>(), <span class="ident">SendError</span><span class="op"><</span><span class="ident">T</span><span class="op">>></span> {
<span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(()))
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Clone</span> <span class="kw">for</span> <span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">clone</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">UnboundedSender</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="ident">UnboundedSender</span>(<span class="self">self</span>.<span class="number">0</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">Clone</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">clone</span>(<span class="kw-2">&</span><span class="self">self</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="comment">// Since this atomic op isn't actually guarding any memory and we don't</span>
<span class="comment">// care about any orderings besides the ordering on the single atomic</span>
<span class="comment">// variable, a relaxed ordering is acceptable.</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">curr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">num_senders</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>);
<span class="kw">loop</span> {
<span class="comment">// If the maximum number of senders has been reached, then fail</span>
<span class="kw">if</span> <span class="ident">curr</span> <span class="op">==</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">max_senders</span>() {
<span class="macro">panic</span><span class="macro">!</span>(<span class="string">"cannot clone `Sender` -- too many outstanding senders"</span>);
}
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">curr</span> <span class="op"><</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">max_senders</span>());
<span class="kw">let</span> <span class="ident">next</span> <span class="op">=</span> <span class="ident">curr</span> <span class="op">+</span> <span class="number">1</span>;
<span class="kw">let</span> <span class="ident">actual</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">num_senders</span>.<span class="ident">compare_and_swap</span>(<span class="ident">curr</span>, <span class="ident">next</span>, <span class="ident">SeqCst</span>);
<span class="comment">// The ABA problem doesn't matter here. We only care that the</span>
<span class="comment">// number of senders never exceeds the maximum.</span>
<span class="kw">if</span> <span class="ident">actual</span> <span class="op">==</span> <span class="ident">curr</span> {
<span class="kw">return</span> <span class="ident">Sender</span> {
<span class="ident">inner</span>: <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">clone</span>(),
<span class="ident">sender_task</span>: <span class="ident">Arc</span>::<span class="ident">new</span>(<span class="ident">Mutex</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>)),
<span class="ident">maybe_parked</span>: <span class="bool-val">false</span>,
};
}
<span class="ident">curr</span> <span class="op">=</span> <span class="ident">actual</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="comment">// Ordering between variables don't matter here</span>
<span class="kw">let</span> <span class="ident">prev</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">num_senders</span>.<span class="ident">fetch_sub</span>(<span class="number">1</span>, <span class="ident">SeqCst</span>);
<span class="kw">if</span> <span class="ident">prev</span> <span class="op">==</span> <span class="number">1</span> {
<span class="kw">let</span> _ <span class="op">=</span> <span class="self">self</span>.<span class="ident">do_send</span>(<span class="prelude-val">None</span>, <span class="bool-val">false</span>);
}
}
}
<span class="comment">/*
*
* ===== impl Receiver =====
*
*/</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">/// Closes the receiving half</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This prevents any further messages from being sent on the channel while</span>
<span class="doccomment">/// still enabling the receiver to drain messages that are buffered.</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="kw">let</span> <span class="kw-2">mut</span> <span class="ident">curr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>);
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">decode_state</span>(<span class="ident">curr</span>);
<span class="kw">if</span> <span class="op">!</span><span class="ident">state</span>.<span class="ident">is_open</span> {
<span class="kw">break</span>
}
<span class="ident">state</span>.<span class="ident">is_open</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="kw">let</span> <span class="ident">next</span> <span class="op">=</span> <span class="ident">encode_state</span>(<span class="kw-2">&</span><span class="ident">state</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="ident">curr</span>, <span class="ident">next</span>, <span class="ident">SeqCst</span>, <span class="ident">SeqCst</span>) {
<span class="prelude-val">Ok</span>(_) <span class="op">=></span> <span class="kw">break</span>,
<span class="prelude-val">Err</span>(<span class="ident">actual</span>) <span class="op">=></span> <span class="ident">curr</span> <span class="op">=</span> <span class="ident">actual</span>,
}
}
<span class="comment">// Wake up any threads waiting as they'll see that we've closed the</span>
<span class="comment">// channel and will continue on their merry way.</span>
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">parked_queue</span>.<span class="ident">pop</span>() } {
<span class="ident">PopResult</span>::<span class="ident">Data</span>(<span class="ident">task</span>) <span class="op">=></span> {
<span class="kw">let</span> <span class="ident">task</span> <span class="op">=</span> <span class="ident">task</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>().<span class="ident">take</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">task</span> {
<span class="ident">task</span>.<span class="ident">notify</span>();
}
}
<span class="ident">PopResult</span>::<span class="ident">Empty</span> <span class="op">=></span> <span class="kw">break</span>,
<span class="ident">PopResult</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> <span class="ident">thread</span>::<span class="ident">yield_now</span>(),
}
}
}
<span class="kw">fn</span> <span class="ident">next_message</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Async</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">// Pop off a message</span>
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">message_queue</span>.<span class="ident">pop</span>() } {
<span class="ident">PopResult</span>::<span class="ident">Data</span>(<span class="ident">msg</span>) <span class="op">=></span> {
<span class="kw">return</span> <span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">msg</span>);
}
<span class="ident">PopResult</span>::<span class="ident">Empty</span> <span class="op">=></span> {
<span class="comment">// The queue is empty, return NotReady</span>
<span class="kw">return</span> <span class="ident">Async</span>::<span class="ident">NotReady</span>;
}
<span class="ident">PopResult</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> {
<span class="comment">// Inconsistent means that there will be a message to pop</span>
<span class="comment">// in a short time. This branch can only be reached if</span>
<span class="comment">// values are being produced from another thread, so there</span>
<span class="comment">// are a few ways that we can deal with this:</span>
<span class="comment">//</span>
<span class="comment">// 1) Spin</span>
<span class="comment">// 2) thread::yield_now()</span>
<span class="comment">// 3) task::current().unwrap() & return NotReady</span>
<span class="comment">//</span>
<span class="comment">// For now, thread::yield_now() is used, but it would</span>
<span class="comment">// probably be better to spin a few times then yield.</span>
<span class="ident">thread</span>::<span class="ident">yield_now</span>();
}
}
}
}
<span class="comment">// Unpark a single task handle if there is one pending in the parked queue</span>
<span class="kw">fn</span> <span class="ident">unpark_one</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="kw">loop</span> {
<span class="kw">match</span> <span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">parked_queue</span>.<span class="ident">pop</span>() } {
<span class="ident">PopResult</span>::<span class="ident">Data</span>(<span class="ident">task</span>) <span class="op">=></span> {
<span class="comment">// Do this step first so that the lock is dropped when</span>
<span class="comment">// `unpark` is called</span>
<span class="kw">let</span> <span class="ident">task</span> <span class="op">=</span> <span class="ident">task</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>().<span class="ident">take</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">task</span> {
<span class="ident">task</span>.<span class="ident">notify</span>();
}
<span class="kw">return</span>;
}
<span class="ident">PopResult</span>::<span class="ident">Empty</span> <span class="op">=></span> {
<span class="comment">// Queue empty, no task to wake up.</span>
<span class="kw">return</span>;
}
<span class="ident">PopResult</span>::<span class="ident">Inconsistent</span> <span class="op">=></span> {
<span class="comment">// Same as above</span>
<span class="ident">thread</span>::<span class="ident">yield_now</span>();
}
}
}
}
<span class="comment">// Try to park the receiver task</span>
<span class="kw">fn</span> <span class="ident">try_park</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">TryPark</span> {
<span class="kw">let</span> <span class="ident">curr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>);
<span class="kw">let</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">decode_state</span>(<span class="ident">curr</span>);
<span class="comment">// If the channel is closed, then there is no need to park.</span>
<span class="kw">if</span> <span class="op">!</span><span class="ident">state</span>.<span class="ident">is_open</span> <span class="op">&&</span> <span class="ident">state</span>.<span class="ident">num_messages</span> <span class="op">==</span> <span class="number">0</span> {
<span class="kw">return</span> <span class="ident">TryPark</span>::<span class="ident">Closed</span>;
}
<span class="comment">// First, track the task in the `recv_task` slot</span>
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">recv_task</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">recv_task</span>.<span class="ident">lock</span>().<span class="ident">unwrap</span>();
<span class="kw">if</span> <span class="ident">recv_task</span>.<span class="ident">unparked</span> {
<span class="comment">// Consume the `unpark` signal without actually parking</span>
<span class="ident">recv_task</span>.<span class="ident">unparked</span> <span class="op">=</span> <span class="bool-val">false</span>;
<span class="kw">return</span> <span class="ident">TryPark</span>::<span class="ident">NotEmpty</span>;
}
<span class="ident">recv_task</span>.<span class="ident">task</span> <span class="op">=</span> <span class="prelude-val">Some</span>(<span class="ident">task</span>::<span class="ident">current</span>());
<span class="ident">TryPark</span>::<span class="ident">Parked</span>
}
<span class="kw">fn</span> <span class="ident">dec_num_messages</span>(<span class="kw-2">&</span><span class="self">self</span>) {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">curr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">inner</span>.<span class="ident">state</span>.<span class="ident">load</span>(<span class="ident">SeqCst</span>);
<span class="kw">loop</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">state</span> <span class="op">=</span> <span class="ident">decode_state</span>(<span class="ident">curr</span>);
<span class="ident">state</span>.<span class="ident">num_messages</span> <span class="op">-=</span> <span class="number">1</span>;
<span class="kw">let</span> <span class="ident">next</span> <span class="op">=</span> <span class="ident">encode_state</span>(<span class="kw-2">&</span><span class="ident">state</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="ident">curr</span>, <span class="ident">next</span>, <span class="ident">SeqCst</span>, <span class="ident">SeqCst</span>) {
<span class="prelude-val">Ok</span>(_) <span class="op">=></span> <span class="kw">break</span>,
<span class="prelude-val">Err</span>(<span class="ident">actual</span>) <span class="op">=></span> <span class="ident">curr</span> <span class="op">=</span> <span class="ident">actual</span>,
}
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Stream</span> <span class="kw">for</span> <span class="ident">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="kw">fn</span> <span class="ident">poll</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, ()<span class="op">></span> {
<span class="kw">loop</span> {
<span class="comment">// Try to read a message off of the message queue.</span>
<span class="kw">let</span> <span class="ident">msg</span> <span class="op">=</span> <span class="kw">match</span> <span class="self">self</span>.<span class="ident">next_message</span>() {
<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">msg</span>) <span class="op">=></span> <span class="ident">msg</span>,
<span class="ident">Async</span>::<span class="ident">NotReady</span> <span class="op">=></span> {
<span class="comment">// There are no messages to read, in this case, attempt to</span>
<span class="comment">// park. The act of parking will verify that the channel is</span>
<span class="comment">// still empty after the park operation has completed.</span>
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">try_park</span>() {
<span class="ident">TryPark</span>::<span class="ident">Parked</span> <span class="op">=></span> {
<span class="comment">// The task was parked, and the channel is still</span>
<span class="comment">// empty, return NotReady.</span>
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">NotReady</span>);
}
<span class="ident">TryPark</span>::<span class="ident">Closed</span> <span class="op">=></span> {
<span class="comment">// The channel is closed, there will be no further</span>
<span class="comment">// messages.</span>
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="prelude-val">None</span>));
}
<span class="ident">TryPark</span>::<span class="ident">NotEmpty</span> <span class="op">=></span> {
<span class="comment">// A message has been sent while attempting to</span>
<span class="comment">// park. Loop again, the next iteration is</span>
<span class="comment">// guaranteed to get the message.</span>
<span class="kw">continue</span>;
}
}
}
};
<span class="comment">// If there are any parked task handles in the parked queue, pop</span>
<span class="comment">// one and unpark it.</span>
<span class="self">self</span>.<span class="ident">unpark_one</span>();
<span class="comment">// Decrement number of messages</span>
<span class="self">self</span>.<span class="ident">dec_num_messages</span>();
<span class="comment">// Return the message</span>
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">Async</span>::<span class="ident">Ready</span>(<span class="ident">msg</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="comment">// Drain the channel of all pending messages</span>
<span class="self">self</span>.<span class="ident">close</span>();
<span class="kw">while</span> <span class="self">self</span>.<span class="ident">next_message</span>().<span class="ident">is_ready</span>() {
<span class="comment">// ...</span>
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">UnboundedReceiver</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// Closes the receiving half</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This prevents any further messages from being sent on the channel while</span>
<span class="doccomment">/// still enabling the receiver to drain messages that are buffered.</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="number">0</span>.<span class="ident">close</span>();
}
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="ident">Stream</span> <span class="kw">for</span> <span class="ident">UnboundedReceiver</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="kw">fn</span> <span class="ident">poll</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, ()<span class="op">></span> {
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">poll</span>()
}
}
<span class="comment">/*
*
* ===== impl Inner =====
*
*/</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="comment">// The return value is such that the total number of messages that can be</span>
<span class="comment">// enqueued into the channel will never exceed MAX_CAPACITY</span>
<span class="kw">fn</span> <span class="ident">max_senders</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">usize</span> {
<span class="kw">match</span> <span class="self">self</span>.<span class="ident">buffer</span> {
<span class="prelude-val">Some</span>(<span class="ident">buffer</span>) <span class="op">=></span> <span class="ident">MAX_CAPACITY</span> <span class="op">-</span> <span class="ident">buffer</span>,
<span class="prelude-val">None</span> <span class="op">=></span> <span class="ident">MAX_BUFFER</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="comment">/*
*
* ===== Helpers =====
*
*/</span>
<span class="kw">fn</span> <span class="ident">decode_state</span>(<span class="ident">num</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="ident">State</span> {
<span class="ident">State</span> {
<span class="ident">is_open</span>: <span class="ident">num</span> <span class="op">&</span> <span class="ident">OPEN_MASK</span> <span class="op">==</span> <span class="ident">OPEN_MASK</span>,
<span class="ident">num_messages</span>: <span class="ident">num</span> <span class="op">&</span> <span class="ident">MAX_CAPACITY</span>,
}
}
<span class="kw">fn</span> <span class="ident">encode_state</span>(<span class="ident">state</span>: <span class="kw-2">&</span><span class="ident">State</span>) <span class="op">-></span> <span class="ident">usize</span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">num</span> <span class="op">=</span> <span class="ident">state</span>.<span class="ident">num_messages</span>;
<span class="kw">if</span> <span class="ident">state</span>.<span class="ident">is_open</span> {
<span class="ident">num</span> <span class="op">|=</span> <span class="ident">OPEN_MASK</span>;
}
<span class="ident">num</span>
}
</pre>
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