Rollup merge of rust-lang#40010 - GuillaumeGomez:barrier-docs, r=frewsxcv

Add missing urls and examples into Barrier structs

r? @frewsxcv

Author: frewsxcv

src/libstd/sync/barrier.rs

@@ -14,6 +14,8 @@ use sync::{Mutex, Condvar};
 /// A barrier enables multiple threads to synchronize the beginning
 /// of some computation.
 ///
+/// # Examples
+///
 /// ```
 /// use std::sync::{Arc, Barrier};
 /// use std::thread;
@@ -50,8 +52,19 @@ struct BarrierState {
 
 /// A result returned from wait.
 ///
-/// Currently this opaque structure only has one method, `.is_leader()`. Only
+/// Currently this opaque structure only has one method, [`.is_leader()`]. Only
 /// one thread will receive a result that will return `true` from this function.
+///
+/// [`.is_leader()`]: #method.is_leader
+///
+/// # Examples
+///
+/// ```
+/// use std::sync::Barrier;
+///
+/// let barrier = Barrier::new(1);
+/// let barrier_wait_result = barrier.wait();
+/// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct BarrierWaitResult(bool);
 
@@ -65,8 +78,18 @@ impl fmt::Debug for Barrier {
 impl Barrier {
     /// Creates a new barrier that can block a given number of threads.
     ///
-    /// A barrier will block `n`-1 threads which call `wait` and then wake up
-    /// all threads at once when the `n`th thread calls `wait`.
+    /// A barrier will block `n`-1 threads which call [`wait`] and then wake up
+    /// all threads at once when the `n`th thread calls [`wait`].
+    ///
+    /// [`wait`]: #method.wait
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Barrier;
+    ///
+    /// let barrier = Barrier::new(10);
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn new(n: usize) -> Barrier {
         Barrier {
@@ -84,10 +107,37 @@ impl Barrier {
     /// Barriers are re-usable after all threads have rendezvoused once, and can
     /// be used continuously.
     ///
-    /// A single (arbitrary) thread will receive a `BarrierWaitResult` that
-    /// returns `true` from `is_leader` when returning from this function, and
+    /// A single (arbitrary) thread will receive a [`BarrierWaitResult`] that
+    /// returns `true` from [`is_leader`] when returning from this function, and
     /// all other threads will receive a result that will return `false` from
-    /// `is_leader`
+    /// [`is_leader`].
+    ///
+    /// [`BarrierWaitResult`]: struct.BarrierWaitResult.html
+    /// [`is_leader`]: struct.BarrierWaitResult.html#method.is_leader
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::{Arc, Barrier};
+    /// use std::thread;
+    ///
+    /// let mut handles = Vec::with_capacity(10);
+    /// let barrier = Arc::new(Barrier::new(10));
+    /// for _ in 0..10 {
+    ///     let c = barrier.clone();
+    ///     // The same messages will be printed together.
+    ///     // You will NOT see any interleaving.
+    ///     handles.push(thread::spawn(move|| {
+    ///         println!("before wait");
+    ///         c.wait();
+    ///         println!("after wait");
+    ///     }));
+    /// }
+    /// // Wait for other threads to finish.
+    /// for handle in handles {
+    ///     handle.join().unwrap();
+    /// }
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn wait(&self) -> BarrierWaitResult {
         let mut lock = self.lock.lock().unwrap();
@@ -120,10 +170,22 @@ impl fmt::Debug for BarrierWaitResult {
 }
 
 impl BarrierWaitResult {
-    /// Returns whether this thread from `wait` is the "leader thread".
+    /// Returns whether this thread from [`wait`] is the "leader thread".
     ///
     /// Only one thread will have `true` returned from their result, all other
     /// threads will have `false` returned.
+    ///
+    /// [`wait`]: struct.Barrier.html#method.wait
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Barrier;
+    ///
+    /// let barrier = Barrier::new(1);
+    /// let barrier_wait_result = barrier.wait();
+    /// println!("{:?}", barrier_wait_result.is_leader());
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn is_leader(&self) -> bool { self.0 }
 }