SimpleAsyncTaskExecutor properly respects NO_CONCURRENCY

Issue: SPR-15895

spring-core/src/main/java/org/springframework/core/task/SimpleAsyncTaskExecutor.java

@@ -48,15 +48,18 @@ import org.springframework.util.concurrent.ListenableFutureTask;
  * @see org.springframework.scheduling.commonj.WorkManagerTaskExecutor
  */
 @SuppressWarnings("serial")
-public class SimpleAsyncTaskExecutor extends CustomizableThreadCreator implements AsyncListenableTaskExecutor, Serializable {
+public class SimpleAsyncTaskExecutor extends CustomizableThreadCreator
+		implements AsyncListenableTaskExecutor, Serializable {
 
 	/**
 	 * Permit any number of concurrent invocations: that is, don't throttle concurrency.
+	 * @see ConcurrencyThrottleSupport#UNBOUNDED_CONCURRENCY
 	 */
 	public static final int UNBOUNDED_CONCURRENCY = ConcurrencyThrottleSupport.UNBOUNDED_CONCURRENCY;
 
 	/**
 	 * Switch concurrency 'off': that is, don't allow any concurrent invocations.
+	 * @see ConcurrencyThrottleSupport#NO_CONCURRENCY
 	 */
 	public static final int NO_CONCURRENCY = ConcurrencyThrottleSupport.NO_CONCURRENCY;
 

spring-core/src/main/java/org/springframework/util/ConcurrencyThrottleSupport.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -93,7 +93,7 @@ public abstract class ConcurrencyThrottleSupport implements Serializable {
 	 * @see #getConcurrencyLimit()
 	 */
 	public boolean isThrottleActive() {
-		return (this.concurrencyLimit > 0);
+		return (this.concurrencyLimit >= 0);
 	}
 
 

spring-core/src/test/java/org/springframework/core/task/SimpleAsyncTaskExecutorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,14 +18,13 @@ package org.springframework.core.task;
 
 import java.util.concurrent.ThreadFactory;
 
-import org.junit.Ignore;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
+
 import org.springframework.util.ConcurrencyThrottleSupport;
 
 import static org.hamcrest.CoreMatchers.*;
-
 import static org.junit.Assert.*;
 
 /**
@@ -39,13 +38,11 @@ public class SimpleAsyncTaskExecutorTests {
 	public final ExpectedException exception = ExpectedException.none();
 
 
-	// TODO Determine why task is executed when concurrency is switched off.
-	@Ignore("Disabled because task is still executed when concurrency is switched off")
 	@Test
 	public void cannotExecuteWhenConcurrencyIsSwitchedOff() throws Exception {
 		SimpleAsyncTaskExecutor executor = new SimpleAsyncTaskExecutor();
 		executor.setConcurrencyLimit(ConcurrencyThrottleSupport.NO_CONCURRENCY);
-		assertFalse(executor.isThrottleActive());
+		assertTrue(executor.isThrottleActive());
 		exception.expect(IllegalStateException.class);
 		executor.execute(new NoOpRunnable());
 	}