Add extension to ExecutorService to return closeable CoroutineDispatcher

Fixes Kotlin#278

Author: deva666

core/kotlinx-coroutines-core/src/main/kotlin/kotlinx/coroutines/experimental/Executors.kt

@@ -16,12 +16,26 @@
 
 package kotlinx.coroutines.experimental
 
+import java.io.Closeable
 import java.util.concurrent.Executor
+import java.util.concurrent.ExecutorService
 import java.util.concurrent.RejectedExecutionException
 import java.util.concurrent.ScheduledExecutorService
 import java.util.concurrent.TimeUnit
 import kotlin.coroutines.experimental.CoroutineContext
 
+/**
+ * [CoroutineDispatcher] that implements [Closeable]
+ */
+abstract class CloseableCoroutineDispatcher: CoroutineDispatcher(), Closeable
+
+/**
+ * Converts an instance of [ExecutorService] to an implementation of [CloseableCoroutineDispatcher].
+ */
+public fun ExecutorService.asCoroutineDispatcher(): CloseableCoroutineDispatcher =
+    // we know that an implementation of Executor.asCoroutineDispatcher actually returns a closeable one
+    (this as Executor).asCoroutineDispatcher() as CloseableCoroutineDispatcher
+
 /**
  * Converts an instance of [Executor] to an implementation of [CoroutineDispatcher].
  * @suppress **Deprecated**: Renamed to [asCoroutineDispatcher].
@@ -42,7 +56,7 @@ private class ExecutorCoroutineDispatcher(override val executor: Executor) : Exe
 /**
  * @suppress **This is unstable API and it is subject to change.**
  */
-public abstract class ExecutorCoroutineDispatcherBase : CoroutineDispatcher(), Delay {
+public abstract class ExecutorCoroutineDispatcherBase : CloseableCoroutineDispatcher(), Delay {
     /**
      * @suppress **This is unstable API and it is subject to change.**
      */
@@ -77,6 +91,10 @@ public abstract class ExecutorCoroutineDispatcherBase : CoroutineDispatcher(), D
             return DefaultExecutor.invokeOnTimeout(time, unit, block)
     }
 
+    override fun close() {
+        (executor as? ExecutorService)?.shutdown()
+    }
+
     override fun toString(): String = executor.toString()
     override fun equals(other: Any?): Boolean = other is ExecutorCoroutineDispatcherBase && other.executor === executor
     override fun hashCode(): Int = System.identityHashCode(executor)

core/kotlinx-coroutines-core/src/test/kotlin/kotlinx/coroutines/experimental/ExecutorsTest.kt

@@ -66,4 +66,15 @@ class ExecutorsTest : TestBase() {
         ctx1.close()
         ctx2.close()
     }
+
+    @Test
+    fun testShutdownExecutorService() {
+        val executorService = Executors.newSingleThreadExecutor { r -> Thread(r, "TestExecutor") }
+        val dispatcher = executorService.asCoroutineDispatcher()
+        runBlocking (dispatcher) {
+            checkThreadName("TestExecutor")
+        }
+        dispatcher.close()
+        check(executorService.isShutdown)
+    }
 }