序

本文主要解析一下shedlock的实现。

LockProvider

shedlock-core-0.16.1-sources.jar!/net/javacrumbs/shedlock/core/LockProvider.java

public interface LockProvider {

    /**
     * @return If empty optional has been returned, lock could not be acquired. The lock
     * has to be released by the callee.
     */
    Optional<SimpleLock> lock(LockConfiguration lockConfiguration);
}

LockProvider入参是lockConfiguration，返回SimpleLock。

StorageBasedLockProvider

shedlock-core-0.16.1-sources.jar!/net/javacrumbs/shedlock/support/StorageBasedLockProvider.java

public class StorageBasedLockProvider implements LockProvider {
    private final StorageAccessor storageAccessor;
    private final LockRecordRegistry lockRecordRegistry = new LockRecordRegistry();

    protected StorageBasedLockProvider(StorageAccessor storageAccessor) {
        this.storageAccessor = storageAccessor;
    }

    @Override
    public Optional<SimpleLock> lock(LockConfiguration lockConfiguration) {
        boolean lockObtained = doLock(lockConfiguration);
        if (lockObtained) {
            return Optional.of(new StorageLock(lockConfiguration, storageAccessor));
        } else {
            return Optional.empty();
        }
    }

    /**
     * Sets lockUntil according to LockConfiguration if current lockUntil &lt;= now
     */
    protected boolean doLock(LockConfiguration lockConfiguration) {
        String name = lockConfiguration.getName();

        if (!lockRecordRegistry.lockRecordRecentlyCreated(name)) {
            // create document in case it does not exist yet
            if (storageAccessor.insertRecord(lockConfiguration)) {
                lockRecordRegistry.addLockRecord(name);
                return true;
            }
            lockRecordRegistry.addLockRecord(name);
        }

        return storageAccessor.updateRecord(lockConfiguration);
    }

    private static class StorageLock implements SimpleLock {
        private final LockConfiguration lockConfiguration;
        private final StorageAccessor storageAccessor;

        StorageLock(LockConfiguration lockConfiguration, StorageAccessor storageAccessor) {
            this.lockConfiguration = lockConfiguration;
            this.storageAccessor = storageAccessor;
        }

        @Override
        public void unlock() {
            storageAccessor.unlock(lockConfiguration);
        }
    }

}

使用StorageAccessor来实现加锁

LockManager

shedlock-core-0.16.1-sources.jar!/net/javacrumbs/shedlock/core/LockManager.java

/**
 * Executes task if not locked.
 */
public interface LockManager {
    void executeWithLock(Runnable task);
}

默认实现
shedlock-core-0.16.1-sources.jar!/net/javacrumbs/shedlock/core/DefaultLockManager.java

public class DefaultLockManager implements LockManager {
    private static final Logger logger = LoggerFactory.getLogger(DefaultLockManager.class);

    private final LockingTaskExecutor lockingTaskExecutor;
    private final LockConfigurationExtractor lockConfigurationExtractor;

    public DefaultLockManager(LockProvider lockProvider, LockConfigurationExtractor lockConfigurationExtractor) {
        this(new DefaultLockingTaskExecutor(lockProvider), lockConfigurationExtractor);
    }

    public DefaultLockManager(LockingTaskExecutor lockingTaskExecutor, LockConfigurationExtractor lockConfigurationExtractor) {
        this.lockingTaskExecutor = requireNonNull(lockingTaskExecutor);
        this.lockConfigurationExtractor = requireNonNull(lockConfigurationExtractor);
    }

    @Override
    public void executeWithLock(Runnable task) {
        Optional<LockConfiguration> lockConfigOptional = lockConfigurationExtractor.getLockConfiguration(task);
        if (!lockConfigOptional.isPresent()) {
            logger.debug("No lock configuration for {}. Executing without lock.", task);
            task.run();
        } else {
            lockingTaskExecutor.executeWithLock(task, lockConfigOptional.get());
        }
    }
}

委托给lockingTaskExecutor来加锁
shedlock-core-0.16.1-sources.jar!/net/javacrumbs/shedlock/core/DefaultLockingTaskExecutor.java

public class DefaultLockingTaskExecutor implements LockingTaskExecutor {
    private static final Logger logger = LoggerFactory.getLogger(DefaultLockingTaskExecutor.class);
    private final LockProvider lockProvider;

    public DefaultLockingTaskExecutor(LockProvider lockProvider) {
        this.lockProvider = requireNonNull(lockProvider);
    }

    @Override
    public void executeWithLock(Runnable task, LockConfiguration lockConfig) {
        Optional<SimpleLock> lock = lockProvider.lock(lockConfig);
        if (lock.isPresent()) {
            try {
                logger.debug("Locked {}.", lockConfig.getName());
                task.run();
            } finally {
                lock.get().unlock();
                logger.debug("Unlocked {}.", lockConfig.getName());
            }
        } else {
            logger.debug("Not executing {}. It's locked.", lockConfig.getName());
        }
    }
}

这里跟lockProvider衔接上

SpringLockableTaskSchedulerFactoryBean(偷梁换柱)

shedlock-spring-0.16.1-sources.jar!/net/javacrumbs/shedlock/spring/SpringLockableTaskSchedulerFactoryBean.java

    @Override
    public Class<?> getObjectType() {
        return LockableTaskScheduler.class;
    }

    @Override
    protected LockableTaskScheduler createInstance() throws Exception {
        return new LockableTaskScheduler(
            taskScheduler,
            new DefaultLockManager(lockProvider, new SpringLockConfigurationExtractor(defaultLockAtMostFor, defaultLockAtLeastFor, embeddedValueResolver))
        );
    }

主要是LockableTaskScheduler的工厂方法

LockableTaskScheduler(task scheduler lock wrapper)

shedlock-spring-0.16.1-sources.jar!/net/javacrumbs/shedlock/spring/LockableTaskScheduler.java

public class LockableTaskScheduler implements TaskScheduler, DisposableBean {
    private final TaskScheduler taskScheduler;
    private final LockManager lockManager;

    public LockableTaskScheduler(TaskScheduler taskScheduler, LockManager lockManager) {
        this.taskScheduler = requireNonNull(taskScheduler);
        this.lockManager = requireNonNull(lockManager);
    }

    @Override
    public ScheduledFuture<?> schedule(Runnable task, Trigger trigger) {
        return taskScheduler.schedule(wrap(task), trigger);
    }

    @Override
    public ScheduledFuture<?> schedule(Runnable task, Date startTime) {
        return taskScheduler.schedule(wrap(task), startTime);
    }

    @Override
    public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, Date startTime, long period) {
        return taskScheduler.scheduleAtFixedRate(wrap(task), startTime, period);
    }

    @Override
    public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, long period) {
        return taskScheduler.scheduleAtFixedRate(wrap(task), period);
    }

    @Override
    public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Date startTime, long delay) {
        return taskScheduler.scheduleWithFixedDelay(wrap(task), startTime, delay);
    }

    @Override
    public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, long delay) {
        return taskScheduler.scheduleWithFixedDelay(wrap(task), delay);
    }

    private Runnable wrap(Runnable task) {
        return new LockableRunnable(task, lockManager);
    }

    @Override
    public void destroy() throws Exception {
        if (taskScheduler instanceof DisposableBean) {
            ((DisposableBean) taskScheduler).destroy();
        }
    }
}

对task scheduler包装了一层，织入了lock的逻辑

问题

上面将了半天，讲了lockProvider以及lockManager，还有LockableTaskScheduler是如何给task scheduler加上锁的，还有LockableTaskScheduler的工厂方法SpringLockableTaskSchedulerFactoryBean。那么问题来了，spring的schedule凭什么就使用你配置的LockableTaskScheduler呢？

@Bean
    public ScheduledLockConfiguration scheduledLockConfiguration(LockProvider lockProvider) {
        return ScheduledLockConfigurationBuilder
                .withLockProvider(lockProvider)
                .withPoolSize(10)
                .withDefaultLockAtMostFor(Duration.ofMinutes(10))
                .build();
    }

这种配置仅仅当spring工厂里头没有配置taskScheduler的时候，起作用。如果项目已经显示指定taskScheduler的时候，那么就不会使用LockableTaskScheduler。不过可以通过实现SchedulingConfigurer接口强制指定使用LockableTaskScheduler。

doc

• 使用shedlock将spring schedule上锁