Add Lock to std

std/shared/src/main/scala/cats/effect/std/Lock.scala

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2020-2023 Typelevel
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cats.effect.std
+
+import cats.effect.kernel.{Concurrent, Poll, Resource}
+import cats.syntax.functor._
+
+abstract class Lock[F[_]] {
+  def shared: Resource[F, Unit]
+  def exclusive: Resource[F, Unit]
+}
+
+object Lock {
+  def apply[F[_]: Concurrent]: F[Lock[F]] = apply(Long.MaxValue)
+
+  def apply[F[_]: Concurrent](maxShared: Long): F[Lock[F]] =
+    Semaphore[F](maxShared).map { semaphore =>
+      new Lock[F] {
+        override def shared: Resource[F, Unit] = semaphore.permit
+        override def exclusive: Resource[F, Unit] =
+          Resource.makeFull((poll: Poll[F]) => poll(semaphore.acquireN(maxShared)))(_ =>
+            semaphore.releaseN(maxShared))
+      }
+    }
+}