src/main/java/com/alipay/remoting/ConnectionPool.java
public void add(Connection connection) {
        markAccess();
        if (null == connection) {
            return;
        }
        boolean res = this.conns.addIfAbsent(connection);
        if (res) {
            connection.increaseRef();
        }
    }
public void add(Connection connection) {
        markAccess();
        if (null == connection) {
            return;
        }
        boolean res = this.conns.addIfAbsent(connection);
        if (res) {
            connection.increaseRef();
        }
    }
add a connection

@param connection