Fix CachedSessionFactory Race

Close the pool so that any sessions returned after the factory is
`destroy()`ed are closed.

* Call `removeAllIdleItems()` in `close()`.

* Close sessions in `SftpStreamingMessageSourceTests`.

**cherry-pick to all supported branches**

# Conflicts:
#	spring-integration-core/src/test/java/org/springframework/integration/util/SimplePoolTests.java

# Conflicts:
#	spring-integration-core/src/test/java/org/springframework/integration/util/SimplePoolTests.java
#	spring-integration-ip/src/main/java/org/springframework/integration/ip/tcp/connection/CachingClientConnectionFactory.java
#	spring-integration-sftp/src/test/java/org/springframework/integration/sftp/inbound/SftpStreamingMessageSourceTests.java

* Remove `default close()` from `Pool` interface
* Cast to `SimplePool` in the `CSF` to call the new `close()`

spring-integration-core/src/main/java/org/springframework/integration/util/SimplePool.java

@@ -60,6 +60,8 @@ public class SimplePool<T> implements Pool<T> {
 
 	private final PoolItemCallback<T> callback;
 
+	private volatile boolean closed;
+
 	/**
 	 * Creates a SimplePool with a specific limit.
 	 * @param poolSize The maximum number of items the pool supports.
@@ -154,6 +156,7 @@ public class SimplePool<T> implements Pool<T> {
 	 * @throws MessagingException if no items become available in time.
 	 */
 	public T getItem() {
+		Assert.state(!this.closed, "Pool has been closed");
 		boolean permitted = false;
 		try {
 			try {
@@ -210,7 +213,7 @@ public class SimplePool<T> implements Pool<T> {
 		Assert.isTrue(this.allocated.contains(item),
 				"You can only release items that were obtained from the pool");
 		if (this.inUse.contains(item)) {
-			if (this.poolSize.get() > this.targetPoolSize.get()) {
+			if (this.poolSize.get() > this.targetPoolSize.get() || this.closed) {
 				this.poolSize.decrementAndGet();
 				if (item != null) {
 					doRemoveItem(item);
@@ -250,6 +253,11 @@ public class SimplePool<T> implements Pool<T> {
 		this.callback.removedFromPool(item);
 	}
 
+	public synchronized void close() {
+		this.closed = true;
+		removeAllIdleItems();
+	}
+
 	/**
 	 * User of the pool provide an implementation of this interface; called during
 	 * various pool operations.

spring-integration-core/src/test/java/org/springframework/integration/util/SimplePoolTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,10 +16,12 @@
 
 package org.springframework.integration.util;
 
+import static org.hamcrest.Matchers.instanceOf;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 
 import java.util.HashSet;
@@ -27,6 +29,7 @@ import java.util.Set;
 import java.util.concurrent.Semaphore;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+
 import org.junit.Test;
 
 import org.springframework.integration.test.util.TestUtils;
@@ -125,13 +128,18 @@ public class SimplePoolTests {
 		assertEquals(2, pool.getAllocatedCount());
 	}
 
-	@Test(expected = IllegalArgumentException.class)
+	@Test
 	public void testForeignObject() {
 		final Set<String> strings = new HashSet<String>();
 		final AtomicBoolean stale = new AtomicBoolean();
 		SimplePool<String> pool = stringPool(2, strings, stale);
 		pool.getItem();
-		pool.releaseItem("Hello, world!");
+		try {
+			pool.releaseItem("Hello, world!");
+		}
+		catch (Exception e) {
+			assertThat(e, instanceOf(IllegalArgumentException.class));
+		}
 	}
 
 	@Test
@@ -150,8 +158,27 @@ public class SimplePoolTests {
 	}
 
 
+	@Test
+	public void testClose() {
+		SimplePool<String> pool = stringPool(10, new HashSet<>(), new AtomicBoolean());
+		String item1 = pool.getItem();
+		String item2 = pool.getItem();
+		pool.releaseItem(item2);
+		assertEquals(2, pool.getAllocatedCount());
+		pool.close();
+		pool.releaseItem(item1);
+		assertEquals(0, pool.getAllocatedCount());
+		try {
+			pool.getItem();
+		}
+		catch (Exception e) {
+			assertThat(e, instanceOf(IllegalStateException.class));
+		}
+	}
+
 	private SimplePool<String> stringPool(int size, final Set<String> strings,
 			final AtomicBoolean stale) {
+
 		SimplePool<String> pool = new SimplePool<String>(size, new SimplePool.PoolItemCallback<String>() {
 			private int i;
 			public String createForPool() {
@@ -168,6 +195,7 @@ public class SimplePoolTests {
 			public void removedFromPool(String item) {
 				strings.remove(item);
 			}
+
 		});
 		return pool;
 	}

spring-integration-file/src/main/java/org/springframework/integration/file/remote/session/CachingSessionFactory.java

@@ -128,7 +128,7 @@ public class CachingSessionFactory<F> implements SessionFactory<F>, DisposableBe
 	 */
 	@Override
 	public void destroy() {
-		this.pool.removeAllIdleItems();
+		this.pool.close();
 	}
 
 	/**

spring-integration-ip/src/main/java/org/springframework/integration/ip/tcp/connection/CachingClientConnectionFactory.java

@@ -21,6 +21,7 @@ import java.util.Map;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
 
+import org.springframework.beans.factory.DisposableBean;
 import org.springframework.core.serializer.Deserializer;
 import org.springframework.core.serializer.Serializer;
 import org.springframework.integration.ip.IpHeaders;
@@ -40,7 +41,7 @@ import org.springframework.messaging.support.ErrorMessage;
  * @since 2.2
  *
  */
-public class CachingClientConnectionFactory extends AbstractClientConnectionFactory {
+public class CachingClientConnectionFactory extends AbstractClientConnectionFactory implements DisposableBean {
 
 	private final AbstractClientConnectionFactory targetConnectionFactory;
 
@@ -403,6 +404,15 @@ public class CachingClientConnectionFactory extends AbstractClientConnectionFact
 		this.targetConnectionFactory.stop(callback);
 	}
 
+	@Override
+	public void destroy() throws Exception {
+		if (this.pool instanceof SimplePool) {
+			((SimplePool) this.pool).close();
+        }
+	}
+
+
+
 	private final class CachedConnection extends TcpConnectionInterceptorSupport {
 
 		private final AtomicBoolean released = new AtomicBoolean();