June 2018 Update

Task/Metered-concurrency/Kotlin/metered-concurrency.kotlin

@@ -0,0 +1,20 @@
+// version 1.1.51
+
+import java.util.concurrent.Semaphore
+import kotlin.concurrent.thread
+
+fun main(args: Array<String>) {
+    val numPermits = 4
+    val numThreads = 9
+    val semaphore = Semaphore(numPermits)
+    for (i in 1..numThreads) {
+        thread {
+            val name = "Unit #$i"
+            semaphore.acquire()
+            println("$name has acquired the semaphore")
+            Thread.sleep(2000)
+            semaphore.release()
+            println("$name has released the semaphore")
+        }
+    }
+}

Task/Metered-concurrency/Scala/metered-concurrency.scala

@@ -0,0 +1,30 @@
+class CountingSemaphore(var maxCount: Int) {
+  private var lockCount = 0
+
+  def acquire(): Unit = {
+    while ( {
+      lockCount >= maxCount
+    }) wait()
+    lockCount += 1
+  }
+
+  def release(): Unit = {
+    if (lockCount > 0) {
+      lockCount -= 1
+      notifyAll()
+    }
+  }
+
+  def getCount: Int = lockCount
+}
+
+object Worker {
+  def main(args: Array[String]): Unit = {
+    val (lock, crew) = (new CountingSemaphore(3), new Array[Worker](5))
+
+    for { i <- 0 until 5} {
+      crew(i) = new Worker(lock, i)
+      crew(i).start()
+    }
+  }
+}