Logger的checksum更新的未加锁问题

[zzzrw]

这里更新校验和在锁之外进行，假设线程 A 写入日志后释放锁，线程 B 获得锁，写入新日志，线程 A 此时才执行 fc.position(0) 写入校验和，结果校验和与日志数据不一致，如果B先更新校验和，就会出现新的校验和被覆盖？
private int calChecksum(int xCheck, byte[] log) {
for (byte b : log) {
xCheck = xCheck * SEED + b;
}
return xCheck;
}

@Override
public void log(byte[] data) {
    byte[] log = wrapLog(data);
    ByteBuffer buf = ByteBuffer.wrap(log);
    lock.lock();
    try {
        fc.position(fc.size());
        fc.write(buf);
    } catch(IOException e) {
        Panic.panic(e);
    } finally {
        lock.unlock();
    }
    updateXChecksum(log);
}


private void updateXChecksum(byte[] log) {
    this.xChecksum = calChecksum(this.xChecksum, log);
    try {
        fc.position(0);
        fc.write(ByteBuffer.wrap(Parser.int2Byte(xChecksum)));
        fc.force(false);
    } catch(IOException e) {
        Panic.panic(e);
    }
}