同步问题和获取 id 生成的集合计数

Question

我在使用 nextMessageId() 时遇到问题，它应该 return 为每条创建的消息分配一个新 ID。然而，每隔一段时间它就不会。它 return 是一个已经使用过的值，我不明白为什么。我试过在 IDE 中调试它，但当我单步执行它时它似乎工作正常。

我正在尝试学习如何使用多线程，如何正确同步方法等。我正在模拟用户发送消息的过程。

基本上每次挖出一个区块时，消息都会从缓冲区复制到当前区块，然后将新区块添加到区块集合中。除了 nextMessageId() 之外，一切似乎都工作正常。感谢任何帮助。

我不想 post 不必要的代码来保持这个 post 尽可能干净，如果需要更多信息，请告诉我。

用户服务class:

public final class UserService extends Service<User, String> {
    ...

    @Override
    public void submit(String message, User user) {
        synchronized (Blockchain.class) {
            MessageEntry messageEntry = MessageEntry.newInstance(repo.nextMessageId(), message, user);
            repo.postMessage(messageEntry);
        }
    }
}

矿工服务class:

public final class MinerService extends Service<Miner, Long> {
    ...

    public void submit(Long number, Miner miner) {
        if (repo.getCurrentBlock().hash(number).startsWith(repo.prefix())) {
            synchronized (Blockchain.class) {
                if (repo.getCurrentBlock().hash(number).startsWith(repo.prefix())) {
                    repo.createBlock(number, miner);
                }
            }
        }
    }
}

Blockchain.class

public class Blockchain {
    ...

    private Deque<Block> blocks;
    private Deque<DataEntry<?>> messageBuffer;
    private Block currentBlock;

    ...

    public long nextMessageId() {
        return blocks.stream()
                .mapToLong(block -> block.getData().size())
                .sum() + messageBuffer.size() + 1L;
    }

    public void postMessage(DataEntry<?> dataEntry) {
        messageBuffer.offerLast(dataEntry);
    }

    public void createBlock(long number, Miner miner) {
        long duration = (new Date().getTime() - currentBlock.getTimestamp()) / 1000;
        Block.ProofOfWork proofOfWork = new Block.ProofOfWork(number, duration, updateN(duration), miner);
        currentBlock.setProofOfWork(proofOfWork);

        if (blocks.offerLast(currentBlock)) {
            currentBlock = generateBlock();
            currentBlock.setData(messageBuffer);
            messageBuffer.clear();
            stateManager.save();
        }
    }
    ...
}

生成5个区块后的消息输出：

Block:
Created by miner # 4
Id: 1
Timestamp: 1637995160818
Magic number: 6489039085832314491
Hash of the previous block: 
0
Hash of the block: 
7cecb0d73c5bbfa925f2c04fba90778c8431e43dc3abd1b0faf1dbc23400321c
Block data: no messages
Block was generating for 0 seconds
N was increased to 1

Block:
Created by miner # 6
Id: 2
Timestamp: 1637995160897
Magic number: 5017000130559711273
Hash of the previous block: 
7cecb0d73c5bbfa925f2c04fba90778c8431e43dc3abd1b0faf1dbc23400321c
Hash of the block: 
0ff1a96574cd8cf9db8c91eeb436df8efd084582251c081409e43e0f17069d51
Block data: 
1 Charles: Life is good
2 Aramys: How bout' those Dolphins?
3 Evelio: Life is good
4 Armando: I love Java
5 Evelio: I love Java
6 Armando: What is the meaning of life?
7 Aramys: I love basketball
8 Charles: How bout' those Dolphins?
Block was generating for 0 seconds
N was increased to 2

Block:
Created by miner # 3
Id: 3
Timestamp: 1637995160918
Magic number: -4429177738817892095
Hash of the previous block: 
0ff1a96574cd8cf9db8c91eeb436df8efd084582251c081409e43e0f17069d51
Hash of the block: 
007577aca398b8fa711229b95f2abb0f959aa73fbaa8939516ca1bea11a467fa
Block data: no messages
Block was generating for 0 seconds
N was increased to 3

Block:
Created by miner # 5
Id: 4
Timestamp: 1637995160932
Magic number: 2352460595297940125
Hash of the previous block: 
007577aca398b8fa711229b95f2abb0f959aa73fbaa8939516ca1bea11a467fa
Hash of the block: 
00053d5c5b0e958f828c12ae74469fdce1e840334cfa4a431504239133c7c612
Block data: 
9 Evelio: How are you?
Block was generating for 0 seconds
N was increased to 4

Block:
Created by miner # 5
Id: 5
Timestamp: 1637995160951
Magic number: 3338207044781263189
Hash of the previous block: 
00053d5c5b0e958f828c12ae74469fdce1e840334cfa4a431504239133c7c612
Hash of the block: 
000093d155de9a54e2143b97d752b7d57031056ec6eb07b9672c5c0815fd9272
Block data: 
9 Armando: This chat is garbage
10 Charles: Interesting...
11 Aramys: Will I ever make decent money?
Block was generating for 0 seconds
N was increased to 5

[1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 10, 11]

编辑：问题是我没有考虑 currentBlock 中保存的 DataEntry（消息）。这解决了问题：

public long nextMessageId() {
    return blocks.stream()
            .mapToLong(block -> block.getData().size())
            .sum() + currentBlock.getData().size() + messageBuffer.size() + 1L;
}

Answer 1

来自您的评论：

The nextMessageId() counts the size of the collection in each block

NextMessageId:

    public long nextMessageId() {
        return blocks.stream()
                .mapToLong(block -> block.getData().size())
                .sum() + messageBuffer.size() + 1L;
    }

您不是还添加了一个额外的 messagebuffer 尺寸吗？

并且在您的 createBlock 方法中，您将清除此缓冲区。于是ID又变小了

同步问题和获取 id 生成的集合计数

Issue with synchronization and getting collection count for id generation

java

multithreading

java-stream

synchronization

thread-safety