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</pre><pre class="rust">
<span class="doccomment">//! Concurrent work-stealing deques.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! These data structures are most commonly used in work-stealing schedulers. The typical setup</span>
<span class="doccomment">//! involves a number of threads, each having its own FIFO or LIFO queue (*worker*). There is also</span>
<span class="doccomment">//! one global FIFO queue (*injector*) and a list of references to *worker* queues that are able to</span>
<span class="doccomment">//! steal tasks (*stealers*).</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! We spawn a new task onto the scheduler by pushing it into the *injector* queue. Each worker</span>
<span class="doccomment">//! thread waits in a loop until it finds the next task to run and then runs it. To find a task, it</span>
<span class="doccomment">//! first looks into its local *worker* queue, and then into the *injector* and *stealers*.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Queues</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [`Injector`] is a FIFO queue, where tasks are pushed and stolen from opposite ends. It is</span>
<span class="doccomment">//! shared among threads and is usually the entry point for new tasks.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [`Worker`] has two constructors:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! * [`new_fifo()`] - Creates a FIFO queue, in which tasks are pushed and popped from opposite</span>
<span class="doccomment">//! ends.</span>
<span class="doccomment">//! * [`new_lifo()`] - Creates a LIFO queue, in which tasks are pushed and popped from the same</span>
<span class="doccomment">//! end.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Each [`Worker`] is owned by a single thread and supports only push and pop operations.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Method [`stealer()`] creates a [`Stealer`] that may be shared among threads and can only steal</span>
<span class="doccomment">//! tasks from its [`Worker`]. Tasks are stolen from the end opposite to where they get pushed.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Stealing</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Steal operations come in three flavors:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! 1. [`steal()`] - Steals one task.</span>
<span class="doccomment">//! 2. [`steal_batch()`] - Steals a batch of tasks and moves them into another worker.</span>
<span class="doccomment">//! 3. [`steal_batch_and_pop()`] - Steals a batch of tasks, moves them into another queue, and pops</span>
<span class="doccomment">//! one task from that worker.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! In contrast to push and pop operations, stealing can spuriously fail with [`Steal::Retry`], in</span>
<span class="doccomment">//! which case the steal operation needs to be retried.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Examples</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! Suppose a thread in a work-stealing scheduler is idle and looking for the next task to run. To</span>
<span class="doccomment">//! find an available task, it might do the following:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! 1. Try popping one task from the local worker queue.</span>
<span class="doccomment">//! 2. Try stealing a batch of tasks from the global injector queue.</span>
<span class="doccomment">//! 3. Try stealing one task from another thread using the stealer list.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! An implementation of this work-stealing strategy:</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! use crossbeam_deque::{Injector, Stealer, Worker};</span>
<span class="doccomment">//! use std::iter;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! fn find_task<T>(</span>
<span class="doccomment">//! local: &Worker<T>,</span>
<span class="doccomment">//! global: &Injector<T>,</span>
<span class="doccomment">//! stealers: &[Stealer<T>],</span>
<span class="doccomment">//! ) -> Option<T> {</span>
<span class="doccomment">//! // Pop a task from the local queue, if not empty.</span>
<span class="doccomment">//! local.pop().or_else(|| {</span>
<span class="doccomment">//! // Otherwise, we need to look for a task elsewhere.</span>
<span class="doccomment">//! iter::repeat_with(|| {</span>
<span class="doccomment">//! // Try stealing a batch of tasks from the global queue.</span>
<span class="doccomment">//! global.steal_batch_and_pop(local)</span>
<span class="doccomment">//! // Or try stealing a task from one of the other threads.</span>
<span class="doccomment">//! .or_else(|| stealers.iter().map(|s| s.steal()).collect())</span>
<span class="doccomment">//! })</span>
<span class="doccomment">//! // Loop while no task was stolen and any steal operation needs to be retried.</span>
<span class="doccomment">//! .find(|s| !s.is_retry())</span>
<span class="doccomment">//! // Extract the stolen task, if there is one.</span>
<span class="doccomment">//! .and_then(|s| s.success())</span>
<span class="doccomment">//! })</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! [`new_fifo()`]: Worker::new_fifo</span>
<span class="doccomment">//! [`new_lifo()`]: Worker::new_lifo</span>
<span class="doccomment">//! [`stealer()`]: Worker::stealer</span>
<span class="doccomment">//! [`steal()`]: Stealer::steal</span>
<span class="doccomment">//! [`steal_batch()`]: Stealer::steal_batch</span>
<span class="doccomment">//! [`steal_batch_and_pop()`]: Stealer::steal_batch_and_pop</span>
<span class="attribute">#![<span class="ident">doc</span>(<span class="ident">test</span>(
<span class="ident">no_crate_inject</span>,
<span class="ident">attr</span>(
<span class="ident">deny</span>(<span class="ident">warnings</span>, <span class="ident">rust_2018_idioms</span>),
<span class="ident">allow</span>(<span class="ident">dead_code</span>, <span class="ident">unused_assignments</span>, <span class="ident">unused_variables</span>)
)
))]</span>
<span class="attribute">#![<span class="ident">warn</span>(
<span class="ident">missing_docs</span>,
<span class="ident">missing_debug_implementations</span>,
<span class="ident">rust_2018_idioms</span>,
<span class="ident">unreachable_pub</span>
)]</span>
<span class="attribute">#![<span class="ident">cfg_attr</span>(<span class="ident">not</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>), <span class="ident">no_std</span>)]</span>
<span class="kw">use</span> <span class="ident">cfg_if::cfg_if</span>;
<span class="macro">cfg_if!</span> {
<span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>)]</span> {
<span class="kw">use</span> <span class="ident">crossbeam_epoch</span> <span class="kw">as</span> <span class="ident">epoch</span>;
<span class="kw">use</span> <span class="ident">crossbeam_utils</span> <span class="kw">as</span> <span class="ident">utils</span>;
<span class="kw">mod</span> <span class="ident">deque</span>;
<span class="kw">pub</span> <span class="kw">use</span> <span class="kw">crate</span><span class="ident">::deque</span>::{<span class="ident">Injector</span>, <span class="ident">Steal</span>, <span class="ident">Stealer</span>, <span class="ident">Worker</span>};
}
}
</pre></div>
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