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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;}@Overridepublic 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 yetif (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;}@Overridepublic 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);}@Overridepublic 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);}@Overridepublic 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

    @Overridepublic Class<?> getObjectType() {return LockableTaskScheduler.class;}@Overrideprotected 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);}@Overridepublic ScheduledFuture<?> schedule(Runnable task, Trigger trigger) {return taskScheduler.schedule(wrap(task), trigger);}@Overridepublic ScheduledFuture<?> schedule(Runnable task, Date startTime) {return taskScheduler.schedule(wrap(task), startTime);}@Overridepublic ScheduledFuture<?> scheduleAtFixedRate(Runnable task, Date startTime, long period) {return taskScheduler.scheduleAtFixedRate(wrap(task), startTime, period);}@Overridepublic ScheduledFuture<?> scheduleAtFixedRate(Runnable task, long period) {return taskScheduler.scheduleAtFixedRate(wrap(task), period);}@Overridepublic ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Date startTime, long delay) {return taskScheduler.scheduleWithFixedDelay(wrap(task), startTime, delay);}@Overridepublic ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, long delay) {return taskScheduler.scheduleWithFixedDelay(wrap(task), delay);}private Runnable wrap(Runnable task) {return new LockableRunnable(task, lockManager);}@Overridepublic 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？

@Beanpublic 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