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sync: do not recommend join_all for Barrier (#3514)

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Alice Ryhl 2021-02-12 10:43:11 +01:00 committed by GitHub
parent 469b43de6a
commit 4099bfdef0
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1 changed files with 15 additions and 9 deletions
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24
tokio/src/sync/barrier.rs
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@ -8,8 +8,6 @@ use std::sync::Mutex;
/// # #[tokio::main]
/// # async fn main() {
/// use tokio::sync::Barrier;
///
/// use futures::future::join_all;
/// use std::sync::Arc;
///
/// let mut handles = Vec::with_capacity(10);
@ -18,17 +16,25 @@ use std::sync::Mutex;
/// let c = barrier.clone();
/// // The same messages will be printed together.
/// // You will NOT see any interleaving.
/// handles.push(async move {
/// handles.push(tokio::spawn(async move {
/// println!("before wait");
/// let wr = c.wait().await;
/// let wait_result = c.wait().await;
/// println!("after wait");
/// wr
/// });
/// wait_result
/// }));
/// }
/// // Will not resolve until all "before wait" messages have been printed
/// let wrs = join_all(handles).await;
///
/// // Will not resolve until all "after wait" messages have been printed
/// let mut num_leaders = 0;
/// for handle in handles {
/// let wait_result = handle.await.unwrap();
/// if wait_result.is_leader() {
/// num_leaders += 1;
/// }
/// }
///
/// // Exactly one barrier will resolve as the "leader"
/// assert_eq!(wrs.into_iter().filter(|wr| wr.is_leader()).count(), 1);
/// assert_eq!(num_leaders, 1);
/// # }
/// ```
#[derive(Debug)]