add dynamic change maxActive support

src/test/java/com/alibaba/druid/benckmark/pool/Case0.java

@@ -49,14 +49,14 @@ public class Case0 extends TestCase {
     public final int COUNT                      = 1000 * 1000 * 1;
 
     protected void setUp() throws Exception {
-//         jdbcUrl = "jdbc:fake:dragoon_v25masterdb";
-//         user = "dragoon25";
-//         password = "dragoon25";
-//         driverClass = "com.alibaba.druid.mock.MockDriver";
+         jdbcUrl = "jdbc:fake:dragoon_v25masterdb";
+         user = "dragoon25";
+         password = "dragoon25";
+         driverClass = "com.alibaba.druid.mock.MockDriver";
 
-        jdbcUrl = "jdbc:mysql://10.20.159.104:3306/masterdb";
-        user = "dragoon";
-        password = "dragoon";
+//        jdbcUrl = "jdbc:mysql://10.20.159.104:3306/masterdb";
+//        user = "dragoon";
+//        password = "dragoon";
     }
 
     public void test_0() throws Exception {

src/test/java/com/alibaba/druid/benckmark/pool/druid/DruidCase0.java

@@ -0,0 +1,42 @@
+package com.alibaba.druid.benckmark.pool.druid;
+
+import java.sql.Connection;
+
+import junit.framework.TestCase;
+
+import com.alibaba.druid.pool.DruidDataSource;
+
+public class DruidCase0 extends TestCase {
+
+    private DruidDataSource dataSource;
+
+    protected void setUp() throws Exception {
+        dataSource = new DruidDataSource();
+        dataSource.setUrl("jdbc:mock:xxx");
+        dataSource.setMaxActive(8);
+        dataSource.setMinIdle(1);
+        dataSource.setMinEvictableIdleTimeMillis(1000 * 60 * 5);
+    }
+
+    protected void tearDown() throws Exception {
+        dataSource.close();
+    }
+
+    public void test_benchmark() throws Exception {
+        for (int i = 0; i < 10; ++i) {
+            long startMillis = System.currentTimeMillis();
+            benchmark();
+            long millis = System.currentTimeMillis() - startMillis;
+            
+            System.out.println("millis : " + millis);
+        }
+    }
+
+    public void benchmark() throws Exception {
+        for (int i = 0; i < 1000 * 1000 * 10; ++i) {
+            Connection conn = dataSource.getConnection();
+            conn.close();
+        }
+    }
+
+}

src/test/java/com/alibaba/druid/bvt/pool/MaxActiveChangeTest.java

@@ -0,0 +1,97 @@
+package com.alibaba.druid.bvt.pool;
+
+import java.sql.Connection;
+
+import junit.framework.Assert;
+import junit.framework.TestCase;
+
+import com.alibaba.druid.pool.DruidDataSource;
+import com.alibaba.druid.pool.GetConnectionTimeoutException;
+import com.alibaba.druid.util.JdbcUtils;
+
+public class MaxActiveChangeTest extends TestCase {
+
+    private DruidDataSource dataSource;
+
+    protected void setUp() throws Exception {
+        dataSource = new DruidDataSource();
+        dataSource.setUrl("jdbc:mock:xxx");
+        dataSource.setTestOnBorrow(false);
+        dataSource.setMaxActive(3);
+        dataSource.setMinIdle(1);
+        dataSource.setMinEvictableIdleTimeMillis(1000 * 60 * 5);
+        dataSource.setMaxWait(20);
+        dataSource.init();
+    }
+
+    protected void tearDown() throws Exception {
+        dataSource.close();
+    }
+
+    public void test_maxActive() throws Exception {
+        for (int i = 0; i < 10; ++i) {
+            Assert.assertEquals(1, connect(1));
+            Assert.assertEquals(1, dataSource.getPoolingCount());
+        }
+        for (int i = 0; i < 10; ++i) {
+            Assert.assertEquals(2, connect(2));
+            Assert.assertEquals(2, dataSource.getPoolingCount());
+        }
+        for (int i = 0; i < 10; ++i) {
+            Assert.assertEquals(3, connect(3));
+            Assert.assertEquals(3, dataSource.getPoolingCount());
+        }
+        for (int i = 0; i < 10; ++i) {
+            Assert.assertEquals(3, connect(4));
+            Assert.assertEquals(3, dataSource.getPoolingCount());
+        }
+        
+        dataSource.setMaxActive(4);
+        
+        for (int i = 0; i < 10; ++i) {
+            Assert.assertEquals(4, connect(4));
+            Assert.assertEquals(4, dataSource.getPoolingCount());
+        }
+        
+        dataSource.shrink();
+        Assert.assertEquals(1, dataSource.getPoolingCount());
+        
+        for (int i = 0; i < 10; ++i) {
+            Assert.assertEquals(4, connect(4));
+            Assert.assertEquals(4, dataSource.getPoolingCount());
+        }
+        
+        Assert.assertEquals(4, dataSource.getPoolingCount());
+        dataSource.setMaxActive(3);
+        
+        Assert.assertEquals(4, dataSource.getPoolingCount());
+        
+        dataSource.shrink();
+        Assert.assertEquals(1, dataSource.getPoolingCount());
+        
+        // 确保收缩之后不会再长上去
+        for (int i = 0; i < 10; ++i) {
+            Assert.assertEquals(3, connect(4));
+            Assert.assertEquals(3, dataSource.getPoolingCount());
+        }
+    }
+
+    public int connect(int count) throws Exception {
+        int successCount = 0;
+        Connection[] connections = new Connection[count];
+        for (int i = 0; i < count; ++i) {
+            try {
+                connections[i] = dataSource.getConnection();
+                successCount++;
+            } catch (GetConnectionTimeoutException e) {
+                // skip
+            }
+        }
+
+        for (int i = 0; i < count; ++i) {
+            JdbcUtils.close(connections[i]);
+        }
+        
+        return successCount;
+    }
+}

src/test/java/com/alibaba/druid/bvt/pool/basic/DataSourceTest3.java

@@ -148,15 +148,7 @@ public class DataSourceTest3 extends TestCase {
 
         conn.close();
 
-        {
-            Exception error = null;
-            try {
-                dataSource.setMaxActive(1);
-            } catch (Exception ex) {
-                error = ex;
-            }
-            Assert.assertNotNull(error);
-        }
+        dataSource.setMaxActive(1);
     }
 
     public void test_error_7() throws Exception {