sync: add Semaphore (#1973)

Provide an asynchronous Semaphore implementation. This is useful for
synchronizing concurrent access to a shared resource.

1 files changed, 4 insertions, 2 deletions

diff --git a/tokio/src/sync/mod.rs b/tokio/src/sync/mod.rs
index df31f8df..a05accbf 100644
--- a/tokio/src/sync/mod.rs
+++ b/tokio/src/sync/mod.rs
@@ -26,7 +26,9 @@ cfg_sync! {
 
     pub mod oneshot;
 
-    pub(crate) mod semaphore;
+    pub(crate) mod semaphore_ll;
+    mod semaphore;
+    pub use semaphore::{Semaphore, SemaphorePermit};
 
     mod task;
     pub(crate) use task::AtomicWaker;
@@ -48,7 +50,7 @@ cfg_not_sync! {
 
     cfg_signal! {
         pub(crate) mod mpsc;
-        pub(crate) mod semaphore;
+        pub(crate) mod semaphore_ll;
     }
 }