環(huán)境

springboot、mybatisPlus、mysql8

mysql8（部署在1核2G的服務器上，很卡，所以下面的數(shù)據(jù)條數(shù)用5000，太大怕不是要等到花兒都謝了 0.0）

原始的for循環(huán)入庫

@Service
@Slf4j
public class MoreTestServiceImpl extends ServiceImpl<MoreTestMapper, MoreTestEntity> implements MoreTestService {

    @Override
    @Transactional(rollbackFor = Exception.class)
    public Object doTest() {
        long start = System.currentTimeMillis();

        List<MoreTestEntity> entityList = new ArrayList<>();
        for (int i = 0; i < 5000; i++) {
            MoreTestEntity entity = new MoreTestEntity();
            entity.setId((long) i);
            entity.setA(UUID.randomUUID().toString());
            entity.setB(UUID.randomUUID().toString());
            entity.setC(UUID.randomUUID().toString());
            entity.setD(UUID.randomUUID().toString());
            entity.setE(UUID.randomUUID().toString());
            entity.setF(UUID.randomUUID().toString());
            entity.setG(UUID.randomUUID().toString());
            entity.setH(UUID.randomUUID().toString());
            entity.setI(UUID.randomUUID().toString());
            entity.setJ(UUID.randomUUID().toString());
            entity.setK(UUID.randomUUID().toString());
            entityList.add(entity);
						
            //在循環(huán)中入庫
            baseMapper.insert(entity);
        }

        long end = System.currentTimeMillis();

        System.err.println(end - start);

        return end - start;
    }
}

共耗時：180121 ms

批量保存操作

@Service
@Slf4j
public class MoreTestServiceImpl extends ServiceImpl<MoreTestMapper, MoreTestEntity> implements MoreTestService {

    @Override
    @Transactional(rollbackFor = Exception.class)
    public Object doTest() {
        long start = System.currentTimeMillis();

        List<MoreTestEntity> entityList = new ArrayList<>();
        for (int i = 0; i < 5000; i++) {
            MoreTestEntity entity = new MoreTestEntity();
            entity.setId((long) i);
            entity.setA(UUID.randomUUID().toString());
            entity.setB(UUID.randomUUID().toString());
            entity.setC(UUID.randomUUID().toString());
            entity.setD(UUID.randomUUID().toString());
            entity.setE(UUID.randomUUID().toString());
            entity.setF(UUID.randomUUID().toString());
            entity.setG(UUID.randomUUID().toString());
            entity.setH(UUID.randomUUID().toString());
            entity.setI(UUID.randomUUID().toString());
            entity.setJ(UUID.randomUUID().toString());
            entity.setK(UUID.randomUUID().toString());
            entityList.add(entity);
        }
				
      	//mybatisPlus提供的批量保存方法，數(shù)字代表每幾條數(shù)據(jù)提交一次事務，默認1000
        saveBatch(entityList, 1000);

        long end = System.currentTimeMillis();

        System.err.println(end - start);

        return end - start;
    }
}

耗時時間：87217ms

在批量插入的基礎(chǔ)上使用多線程

@Service
@Slf4j
public class MoreTestServiceImpl extends ServiceImpl<MoreTestMapper, MoreTestEntity> implements MoreTestService {

    @Override
    @Transactional(rollbackFor = Exception.class)
    public Object doTest() throws InterruptedException {
        long start = System.currentTimeMillis();

        //手動創(chuàng)建線程池，注意你 數(shù)據(jù)庫連接池的 允許連接數(shù)量，別超過了就行。
        ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(
                5,
                5,
                30,
                TimeUnit.SECONDS,
                new LinkedBlockingDeque<>(10),
                //isDaemon 設(shè)置線程是否是守護線程，true的話，主線程結(jié)束，new的線程就不會繼續(xù)工作
                new NamedThreadFactory("執(zhí)行線程", false),
                (r, executor) -> System.out.println("拒絕" + r));


        List<MoreTestEntity> entityList = new ArrayList<>();
        for (int i = 0; i < 5000; i++) {
            MoreTestEntity entity = new MoreTestEntity();
            entity.setId((long) i);
            entity.setA(UUID.randomUUID().toString());
            entity.setB(UUID.randomUUID().toString());
            entity.setC(UUID.randomUUID().toString());
            entity.setD(UUID.randomUUID().toString());
            entity.setE(UUID.randomUUID().toString());
            entity.setF(UUID.randomUUID().toString());
            entity.setG(UUID.randomUUID().toString());
            entity.setH(UUID.randomUUID().toString());
            entity.setI(UUID.randomUUID().toString());
            entity.setJ(UUID.randomUUID().toString());
            entity.setK(UUID.randomUUID().toString());
            entityList.add(entity);
        }

        //拆分list，將其拆分成5份，然后上面線程池創(chuàng)建也是5個核心線程，剛好執(zhí)行
        List<List<MoreTestEntity>> partition = ListUtils.partition(entityList, 1000);
        //使用CountDownLatch保證所有線程都執(zhí)行完成
        CountDownLatch latch = new CountDownLatch(5);
        partition.forEach(item -> {
            poolExecutor.execute(() -> {
                saveBatch(item, 1000);
                latch.countDown();
            });
        });
        latch.await();
        // 也可以這么寫，設(shè)定超時時間
        //latch.await(100,TimeUnit.SECONDS);
        long end = System.currentTimeMillis();

        System.err.println(end - start);
        //關(guān)閉線程池
        poolExecutor.shutdown();
        return end - start;
    }
}

耗時時間： 28235

可見時間從180秒，縮短到了28秒，但是@Transactional對于多線程是控制不了所有的事務的。

Spring實現(xiàn)事務的原理是通過ThreadLocal把數(shù)據(jù)庫連接綁定到當前線程中，同一個事務中數(shù)據(jù)庫操作使用同一個jdbc connection，新開啟的線程獲取不到當前jdbc connection。

如下代碼：

partition.forEach(item -> {
            poolExecutor.execute(() -> {
                saveBatch(item, 1000);
                latch.countDown();
                //讓每個都報錯
                int i = 1/0;
            });
        });

控制臺打印：

Exception in thread "執(zhí)行線程5" java.lang.ArithmeticException: / by zero
	at com.kusch.ares.service.impl.MoreTestServiceImpl.lambda$null$1(MoreTestServiceImpl.java:68)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:750)
Exception in thread "執(zhí)行線程2" java.lang.ArithmeticException: / by zero
	at com.kusch.ares.service.impl.MoreTestServiceImpl.lambda$null$1(MoreTestServiceImpl.java:68)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:750)
Exception in thread "執(zhí)行線程4" java.lang.ArithmeticException: / by zero
	at com.kusch.ares.service.impl.MoreTestServiceImpl.lambda$null$1(MoreTestServiceImpl.java:68)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:750)
Exception in thread "執(zhí)行線程1" java.lang.ArithmeticException: / by zero
	at com.kusch.ares.service.impl.MoreTestServiceImpl.lambda$null$1(MoreTestServiceImpl.java:68)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:750)
Exception in thread "執(zhí)行線程3" 30179
java.lang.ArithmeticException: / by zero
	at com.kusch.ares.service.impl.MoreTestServiceImpl.lambda$null$1(MoreTestServiceImpl.java:68)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:750)

可見5個線程都報錯了，但是去查詢數(shù)據(jù)庫，卻可以查詢到5000條數(shù)據(jù)，這是不應該出現(xiàn)的情況。

處理多線程入庫的事務問題

@Service
@Slf4j
public class MoreTestServiceImpl extends ServiceImpl<MoreTestMapper, MoreTestEntity> implements MoreTestService {

    @Resource
    private DataSourceTransactionManager dataSourceTransactionManager;
    @Resource
    private TransactionDefinition transactionDefinition;

    @Override
    //此處手動管理事務的提交后，這個注解就可以去掉了
    //    @Transactional(rollbackFor = Exception.class)
    public Object doTest() {
        long start = System.currentTimeMillis();

        //手動創(chuàng)建線程池，注意你 數(shù)據(jù)庫連接池的 允許連接數(shù)量，別超過了就行。
        ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(
                5,
                5,
                30,
                TimeUnit.SECONDS,
                new LinkedBlockingDeque<>(10),
                //isDaemon 設(shè)置線程是否是守護線程，true的話，主線程結(jié)束，new的線程就不會繼續(xù)工作
                new NamedThreadFactory("執(zhí)行線程", false),
                (r, executor) -> System.out.println("拒絕" + r));


        List<MoreTestEntity> entityList = new ArrayList<>();
        for (int i = 0; i < 50; i++) {
            MoreTestEntity entity = new MoreTestEntity();
            entity.setId((long) i);
            entity.setA(UUID.randomUUID().toString());
            entity.setB(UUID.randomUUID().toString());
            entity.setC(UUID.randomUUID().toString());
            entity.setD(UUID.randomUUID().toString());
            entity.setE(UUID.randomUUID().toString());
            entity.setF(UUID.randomUUID().toString());
            entity.setG(UUID.randomUUID().toString());
            entity.setH(UUID.randomUUID().toString());
            entity.setI(UUID.randomUUID().toString());
            entity.setJ(UUID.randomUUID().toString());
            entity.setK(UUID.randomUUID().toString());
            entityList.add(entity);
        }

        //拆分list，將其拆分成5份，然后上面線程池創(chuàng)建也是5個核心線程，剛好執(zhí)行
        List<List<MoreTestEntity>> partition = ListUtils.partition(entityList, 10);
        //使用CountDownLatch保證所有線程都執(zhí)行完成
        CountDownLatch sonLatch = new CountDownLatch(5);
        //主線程的 肯定為1
        CountDownLatch mainLatch = new CountDownLatch(1);
        AtomicBoolean hasError = new AtomicBoolean(false);
        partition.forEach(item -> {
            poolExecutor.execute(() -> {
                doSave(item, sonLatch, hasError, mainLatch);
            });
        });

        try {
            //此處應該是用try catch 包裹著主線程的所有業(yè)務代碼，以此保證主線程中任何一處報錯都可以通知子線程

            //這里加一個是為了調(diào)試主線程中的數(shù)據(jù)入庫操作
            MoreTestEntity entity = new MoreTestEntity();
            entity.setId((long) 99999);
            entity.setA(UUID.randomUUID().toString());
            entity.setB(UUID.randomUUID().toString());
            entity.setC(UUID.randomUUID().toString());
            entity.setD(UUID.randomUUID().toString());
            entity.setE(UUID.randomUUID().toString());
            entity.setF(UUID.randomUUID().toString());
            entity.setG(UUID.randomUUID().toString());
            entity.setH(UUID.randomUUID().toString());
            entity.setI(UUID.randomUUID().toString());
            entity.setJ(UUID.randomUUID().toString());
            entity.setK(UUID.randomUUID().toString());
            save(entity);

            //主線程報錯
            int i = 10 / 0;

            sonLatch.await();
        } catch (InterruptedException e) {
            hasError.set(true);
            e.printStackTrace();
        }

        mainLatch.countDown();

        long end = System.currentTimeMillis();

        System.err.println(end - start);
        //關(guān)閉線程池
        if (!poolExecutor.isShutdown()) {
            poolExecutor.shutdown();
        }
        return end - start;
    }

    /**
     * 包裝后的子線程的保存代碼
     *
     * @param entityList 要保存的集合
     * @param sonLatch   子線程 CountDownLatch
     * @param hasError   是否發(fā)生錯誤
     * @param mainLatch  主線程 CountDownLatch
     */
    private void doSave(List<MoreTestEntity> entityList,
                        CountDownLatch sonLatch,
                        AtomicBoolean hasError,
                        CountDownLatch mainLatch) {
        TransactionStatus transactionStatus = dataSourceTransactionManager.getTransaction(transactionDefinition);
        try {

            //            //子線程報錯
            //            int i = 10 / 0;

            saveBatch(entityList);

        } catch (Throwable throwable) {
            throwable.printStackTrace();
            hasError.set(true);
        } finally {
            //這是必須的，每個子線程走完，要讓主線程繼續(xù)走，然后再回到子線程的每個任務，決定是提交還是回滾
            sonLatch.countDown();
        }
        try {
            //等待主線程的執(zhí)行結(jié)束
            mainLatch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
            hasError.set(true);
        }

        //事務操作
        if (hasError.get()) {
            dataSourceTransactionManager.rollback(transactionStatus);
        } else {
            dataSourceTransactionManager.commit(transactionStatus);
        }

    }

}

分別放開子線程報錯和主線程報錯，會發(fā)現(xiàn)事務都可以正?；貪L，達到了預期的效果。

主要思路就是通過子線程CountDownLatch和主線程CountDownLatch，控制線程好代碼的執(zhí)行順序即可。

最后補充幾點：文章來源地址http://www.zghlxwxcb.cn/news/detail-431324.html

• 上述代碼中的countDown()一旦出現(xiàn)不執(zhí)行的情況那會導致線程堵塞堆積，所以建議給await()增加超時時間
• 這樣操作可能還會出現(xiàn)問題，比如主線程通知子線程可以進行實務操作了，但是各個子線程之間非透明，所以還是有幾率存在某個子線程事務回滾失敗的情況。

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