#vulnerable code 
                                static void setBlockSize(int blockSize) {
        BLOCK_SIZE = blockSize;
        synchronized (BlocksPool.class) { // can be easily changed to lock-free
            instance = new BlocksPool();
        }
    } 
                            #location 4 
                            #vulnerability type THREAD_SAFETY_VIOLATION
#fixed code
                                static void setBlockSize(int blockSize) {
        synchronized (BlocksPool.class) { // can be easily changed to lock-free
            instance = new BlocksPool(blockSize);
        }
    }