Introduce application coroutine scope

ktor-server/ktor-server-core/src/io/ktor/application/Application.kt

@@ -1,15 +1,24 @@
 package io.ktor.application
 
+import kotlinx.coroutines.*
+
 /**
- * Represents configured and running web application, capable of handling requests
+ * Represents configured and running web application, capable of handling requests.
+ * It is also the application coroutine scope that is cancelled immediately at application stop so useful
+ * for launching background coroutines.
  *
  * @param environment Instance of [ApplicationEnvironment] describing environment this application runs in
  */
-class Application(val environment: ApplicationEnvironment) : ApplicationCallPipeline() {
+class Application(val environment: ApplicationEnvironment) : ApplicationCallPipeline(), CoroutineScope {
+    private val applicationJob = SupervisorJob(environment.parentCoroutineContext[Job])
+
+    override val coroutineContext = environment.parentCoroutineContext + applicationJob
+
     /**
      * Called by [ApplicationEngine] when [Application] is terminated
      */
     fun dispose() {
+        applicationJob.cancel()
         uninstallAllFeatures()
     }
 }

ktor-server/ktor-server-test-host/src/io/ktor/server/testing/EngineTestSuite.kt

@@ -20,7 +20,6 @@ import kotlinx.coroutines.io.*
 import kotlinx.coroutines.io.jvm.javaio.*
 import kotlinx.io.core.*
 import kotlinx.io.streams.*
-import org.junit.Test
 import org.junit.runners.model.*
 import org.slf4j.*
 import java.io.*
@@ -34,6 +33,7 @@ import java.util.zip.*
 import kotlin.concurrent.*
 import kotlin.coroutines.*
 import kotlin.test.*
+import kotlin.test.Test
 
 @Suppress("KDocMissingDocumentation")
 abstract class EngineTestSuite<TEngine : ApplicationEngine, TConfiguration : ApplicationEngine.Configuration>(
@@ -1674,6 +1674,21 @@ abstract class EngineTestSuite<TEngine : ApplicationEngine, TConfiguration : App
         }
     }
 
+    @Test
+    fun testApplicationScopeCancellation() {
+        var job: Job? = null
+
+        createAndStartServer {
+            job = application.launch {
+                delay(10000000L)
+            }
+        }
+
+        server!!.stop(1, 10, TimeUnit.SECONDS)
+        assertNotNull(job)
+        assertTrue { job!!.isCancelled }
+    }
+
     private fun String.urlPath() = replace("\\", "/")
     private class ExpectedException(message: String) : RuntimeException(message)