Auto merge of rust-lang#126839 - obeis:mpmc, r=Amanieu

Add multi-producer, multi-consumer channel (mpmc)

Closes rust-lang#125712

Tracking issue: rust-lang#126840

r? m-ou-se

Author: bors

std/src/lib.rs

@@ -153,7 +153,7 @@
 //! the [`io`], [`fs`], and [`net`] modules.
 //!
 //! The [`thread`] module contains Rust's threading abstractions. [`sync`]
-//! contains further primitive shared memory types, including [`atomic`] and
+//! contains further primitive shared memory types, including [`atomic`], [`mpmc`] and
 //! [`mpsc`], which contains the channel types for message passing.
 //!
 //! # Use before and after `main()`
@@ -177,6 +177,7 @@
 //! - after-main use of thread-locals, which also affects additional features:
 //!   - [`thread::current()`]
 //!   - [`thread::scope()`]
+//!   - [`sync::mpmc`]
 //!   - [`sync::mpsc`]
 //! - before-main stdio file descriptors are not guaranteed to be open on unix platforms
 //!
@@ -202,6 +203,7 @@
 //! [`atomic`]: sync::atomic
 //! [`for`]: ../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
 //! [`str`]: prim@str
+//! [`mpmc`]: sync::mpmc
 //! [`mpsc`]: sync::mpsc
 //! [`std::cmp`]: cmp
 //! [`std::slice`]: mod@slice

std/src/sync/mod.rs

@@ -133,6 +133,11 @@
 //!   inter-thread synchronisation mechanism, at the cost of some
 //!   extra memory.
 //!
+//! - [`mpmc`]: Multi-producer, multi-consumer queues, used for
+//!   message-based communication. Can provide a lightweight
+//!   inter-thread synchronisation mechanism, at the cost of some
+//!   extra memory.
+//!
 //! - [`Mutex`]: Mutual Exclusion mechanism, which ensures that at
 //!   most one thread at a time is able to access some data.
 //!
@@ -153,6 +158,7 @@
 //! [`Arc`]: crate::sync::Arc
 //! [`Barrier`]: crate::sync::Barrier
 //! [`Condvar`]: crate::sync::Condvar
+//! [`mpmc`]: crate::sync::mpmc
 //! [`mpsc`]: crate::sync::mpsc
 //! [`Mutex`]: crate::sync::Mutex
 //! [`Once`]: crate::sync::Once
@@ -193,12 +199,13 @@ pub use self::rwlock::{MappedRwLockReadGuard, MappedRwLockWriteGuard};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::rwlock::{RwLock, RwLockReadGuard, RwLockWriteGuard};
 
+#[unstable(feature = "mpmc_channel", issue = "126840")]
+pub mod mpmc;
 pub mod mpsc;
 
 mod barrier;
 mod condvar;
 mod lazy_lock;
-mod mpmc;
 mod mutex;
 pub(crate) mod once;
 mod once_lock;

std/src/sync/mpmc/error.rs

@@ -7,6 +7,7 @@ use crate::{error, fmt};
 ///
 /// [`send_timeout`]: super::Sender::send_timeout
 #[derive(PartialEq, Eq, Clone, Copy)]
+#[unstable(feature = "mpmc_channel", issue = "126840")]
 pub enum SendTimeoutError<T> {
     /// The message could not be sent because the channel is full and the operation timed out.
     ///
@@ -18,12 +19,14 @@ pub enum SendTimeoutError<T> {
     Disconnected(T),
 }
 
+#[unstable(feature = "mpmc_channel", issue = "126840")]
 impl<T> fmt::Debug for SendTimeoutError<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         "SendTimeoutError(..)".fmt(f)
     }
 }
 
+#[unstable(feature = "mpmc_channel", issue = "126840")]
 impl<T> fmt::Display for SendTimeoutError<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match *self {
@@ -33,8 +36,10 @@ impl<T> fmt::Display for SendTimeoutError<T> {
     }
 }
 
+#[unstable(feature = "mpmc_channel", issue = "126840")]
 impl<T> error::Error for SendTimeoutError<T> {}
 
+#[unstable(feature = "mpmc_channel", issue = "126840")]
 impl<T> From<SendError<T>> for SendTimeoutError<T> {
     fn from(err: SendError<T>) -> SendTimeoutError<T> {
         match err {