#vulnerable code 
                                public void putBlock(Block block) throws Exception {
        rocksDB.put((BLOCKS_BUCKET_PREFIX + block.getHash()).getBytes(), SerializeUtils.serialize(block));
    } 
                            #location 2 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                public void putBlock(Block block) throws Exception {
        byte[] key = SerializeUtils.serialize(BLOCKS_BUCKET_PREFIX + block.getHash());
        rocksDB.put(key, SerializeUtils.serialize(block));
    }