[pull] master from DefinitelyTyped:master

types/semaphore/index.d.ts

@@ -1,8 +1,17 @@
 declare function semaphore(capacity?: number): semaphore.Semaphore;
 
 declare namespace semaphore {
+    /**
+     * Releases `n` (default `1`) units of capacity back to the semaphore.
+     */
+    type Leave = (n?: number) => void;
+
     interface Task {
-        (): void;
+        /**
+         * @param leave Releases the capacity held by this task. `take` passes it to every
+         * task it runs, so a task can release the semaphore without closing over it.
+         */
+        (leave: Leave): void;
     }
 
     interface Semaphore {

types/semaphore/semaphore-tests.ts

@@ -13,3 +13,16 @@ sem.leave(2);
 sem.current;
 
 const available: boolean = sem.available(2);
+
+// `take` passes `leave` to every task, so a task can release the semaphore
+// without closing over it. Tasks that ignore it still type-check.
+sem.take((leave: semaphore.Leave) => {
+    console.log("My task");
+    leave();
+});
+
+sem.take(2, (leave) => {
+    // $ExpectType Leave
+    leave;
+    leave(2);
+});