#vulnerable code 
                                public static IpPool getIpPool() {
        if (ipPool == null) {
            synchronized (IpPoolHolder.class) {
                if (ipPool == null) {
                    ipPool = IpPool.create(DungProxyContext.create().buildDefaultConfigFile().handleConfig());
                }
            }
        }
        return ipPool;
    } 
                            #location 9 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                public static IpPool getIpPool() {
        if (ipPool == null) {
            synchronized (IpPoolHolder.class) {
                if (ipPool == null) {
                    ipPool = IpPool.create(DungProxyContext.create().buildDefaultConfigFile());
                }
            }
        }
        return ipPool;
    }