[alibaba/druid]1.2.6版本中仍然存在同一个holder在connections出现两次的问题，高并发下会出现statement is closed等问题。

minEvictableIdleTimeMillis=100000 setMaxEvictableIdleTimeMillis=1000L 60L 60L * 7 keepAliveBetweenTimeMillis=120000 minIdle=2 timeBetweenEvictionRunsMillis=70000 validationQuery=select 1 keepAlive=true

    DruidDataSource druidDataSource = new DruidDataSource();
    druidDataSource.setUsername("");
    druidDataSource.setPassword("");
    druidDataSource.setUrl("jdbc:mysql://192.168.253.129:3306/user?characterEncoding=utf8&autoReconnect=true&zeroDateTimeBehavior=convertToNull&serverTimezone=UTC&useSSL=false&allowMultiQueries=true");
    druidDataSource.setValidationQuery("select 1");
    druidDataSource.setMinEvictableIdleTimeMillis(100000);
    druidDataSource.setMaxEvictableIdleTimeMillis(DEFAULT_MAX_EVICTABLE_IDLE_TIME_MILLIS);
    druidDataSource.setKeepAliveBetweenTimeMillis(120000);
    druidDataSource.setMinIdle(2);
    druidDataSource.setTimeBetweenEvictionRunsMillis(70000);
    druidDataSource.setKeepAlive(true);
    DruidPooledConnection connection1 = druidDataSource.getConnection();
    DruidPooledConnection connection2 = druidDataSource.getConnection();
    connection2.close();
    Thread.sleep(95000);
    connection1.close();
    Thread.sleep(140000);
    DruidPooledConnection connection3 = druidDataSource.getConnection();
    DruidPooledConnection connection4 = druidDataSource.getConnection();
    System.out.println(connection3.getConnectionHolder() == connection4.getConnectionHolder());
    connection3.close();
    connection4.close();

问题出现在DestoryTask的shrink函数中。 时间点70000ms时：connections[connection2],connection2的空闲时间均小于minEvictableIdleTimeMillis和keepAliveBetweenTimeMillis跳过

时间点95000时，connection1返还连接池，此时connections[connection2,connection1]，connections中的元素空闲时间是递减的

时间点140000ms时，connection2因为空闲时间大于120000会加到keepConnections数组中，后返还，返还时未修改lastActiveTimeMillis，此时connections[connection1,connection2]，connection2的空闲时间比connection1的要大

时间点210000ms时，connections1因为空闲时间大于100000，但由于设置minidel=2会跳过shrink中所有if代码块，connections2由于空闲时间大于120000，会加入keepconnection中。进而导致connections会有两个相同的holder

1.2.6版本中限制timeBetweenEvictionRunsMillis小于keepAliveBetweenTimeMillis并不能解决问题。该问题出现的原因还是shrink函数中connections拷贝的bug，希望官方能解决这个bug，可参考pullrequest：https://github.com/alibaba/druid/pull/4218

另一方面keepConnection放回connections未修改lastActiveTimeMills，会导致connections的空闲时间不是递减的。

@wenshao