弹簧引导: ReentrantLock

Question

我编写了一个@Repository类：

@Repository
public class RepositoryDocumentDao {

    private static final Logger LOG = LoggerFactory.getLogger(RepositoryDocumentDao.class);
    private ReentrantLock lock;

    @Autowired
    public RepositoryDocumentDao(
    ) {
        this.lock = new ReentrantLock();
    }
}

我的相关代码是：

private boolean verifyStorageSize(long requiredBytes) {
    this.lock.lock();
    LOG.debug("IN");
    //.. do someting large
    LOG.debug("OUT");
    this.lock.unlock();
}

我查看了日志，并在受保护的代码中输入了两个线程：

http-nio-8080-exec-3 =================IN=================  
...
http-nio-8080-exec-10 =================IN================= 

有什么想法吗？

Answer 1

--我无法重现您提到的的情况，但我为您提供了一个简单的示例，说明了如何实现代码。

    @RestController
    @RequestMapping("/event")
    public class EventRestController extends BaseRestController {

        private final EventService service;

        @Autowired
        public EventRestController(final EventService service) {
            this.service = requireNonNull(service, "service can't be null");
        }

        @PutMapping(value = "/sync")
        public Callable<ResponseEntity<Void>> syncOperation() {
            return () -> service.syncOperation();
        }
    ...
    }

    @Service
    @Slf4j
    public class EventServiceImpl implements EventService {

        private final EventRepository repository;
        private final ReentrantLock fairLock;

        @Autowired
        public EventServiceImpl(@Qualifier("eventRepository") final EventRepository repository) {
            this.repository = requireNonNull(repository, "repository can't be null");
            this.fairLock = new ReentrantLock(true);
        }

        @Override
        public void syncOperation() {
            log.debug("thread try to acquire lock");
            boolean isLockAcquired = false;
            try {
               isLockAcquired = fairLock.tryLock(10, TimeUnit.SECONDS);
            } catch (InterruptedException e) {
               throw new IllegalStateException(e);
            }

            if (isLockAcquired) {
               try {
                  log.debug("{} own the lock", Thread.currentThread().getName());
                  // heavy operation
                  Thread.sleep(2000);
               } catch (InterruptedException e) {
                  throw new IllegalStateException(e);
               } finally {
                  fairLock.unlock();
                  log.debug("thread unlock");
               }
           }

           log.debug("thread - {} end of method", Thread.currentThread().getName());
       }
    ...
}

Bash代码调用端点：

#!/bin/bash

MAX=$1

for (( c=1; c<=MAX; c++ ))
do
   curl -X PUT http://localhost:2000/app/event/sync > /dev/null 2>&1 &
done

调用：

./sync.sh 5

它将在后台启动5个进程，5个并发进程将调用端点。

日志消息：

15:59:22.026 [task-1] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread try to aquire lock
15:59:22.026 [task-2] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread try to aquire lock
15:59:22.026 [task-3] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread try to aquire lock
15:59:22.026 [task-5] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread try to aquire lock
15:59:22.026 [task-4] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread try to aquire lock
15:59:22.026 [task-2] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - task-2 own the lock
15:59:24.027 [task-2] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread unlock
15:59:24.027 [task-3] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - task-3 own the lock
15:59:24.027 [task-2] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread - task-2 end of method
15:59:26.027 [task-3] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread unlock
15:59:26.028 [task-3] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread - task-3 end of method
15:59:26.028 [task-1] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - task-1 own the lock
15:59:28.029 [task-1] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread unlock
15:59:28.029 [task-5] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - task-5 own the lock
15:59:28.029 [task-1] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread - task-1 end of method

在这个示例中，我们可以看到任务-2线程成功地获得了锁，其他线程试图锁定，直到任务-2释放锁为止，而线程-4没有在适当的时间获得锁。

我觉得这部分很有趣：

15:59:22.026 [task-2] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - task-2 own the lock
15:59:24.027 [task-2] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread unlock
15:59:24.027 [task-3] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - task-3 own the lock
15:59:24.027 [task-2] DEBUG hu.gaszabo.persistence.app.application.EventServiceImpl - thread - task-2 end of method

任务-2线程获得了锁，2秒后它释放了锁，任务-3线程在任务之前立即获得了锁-2线程扭曲了“方法的结束”消息。

您的问题的答案可以是，某些操作是在同一时间发生的(查看时间戳会更好)，但它会按照日志中的顺序向您显示您可能误解的内容(例如，我显示的内容代表了这种情况)。