sync: add RwLock (#1699)

Provides a `RwLock` based on a semaphore. The semaphore is initialized
with 32 permits. A read acquires a single permit and a write acquires all 32
permits. This ensures that reads (up to 32) may happen concurrently and
writes happen exclusively.

1 files changed, 3 insertions, 0 deletions

diff --git a/tokio/src/sync/mod.rs b/tokio/src/sync/mod.rs
index 6ed91607..beb96920 100644
--- a/tokio/src/sync/mod.rs
+++ b/tokio/src/sync/mod.rs
@@ -32,6 +32,9 @@ cfg_sync! {
     mod semaphore;
     pub use semaphore::{Semaphore, SemaphorePermit};
 
+    mod rwlock;
+    pub use rwlock::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+
     mod task;
     pub(crate) use task::AtomicWaker;