网站域名查询系统,北京广告网站建设,一个网站一个月发多少外链比较合适,网站建设 中企动力 石家庄介绍 在我以前的文章中 #xff0c;我介绍了OPTIMISTIC_FORCE_INCREMENT锁定模式#xff0c;并将其应用于将子实体版本更改传播到锁定的父实体。 在本文中#xff0c;我将介绍PESSIMISTIC_FORCE_INCREMENT锁定模式#xff0c;并将其与乐观的锁定模式进行比较。 相像多于不… 介绍 在我以前的文章中 我介绍了OPTIMISTIC_FORCE_INCREMENT锁定模式并将其应用于将子实体版本更改传播到锁定的父实体。 在本文中我将介绍PESSIMISTIC_FORCE_INCREMENT锁定模式并将其与乐观的锁定模式进行比较。 相像多于不同 正如我们已经发现的那样即使当前事务没有修改锁定的实体状态 OPTIMISTIC_FORCE_INCREMENT锁定模式也可以增加实体版本。 对于每种锁定模式Hibernate定义一个关联的LockingStrategy 并且OPTIMISTIC_FORCE_INCREMENT锁定模式事件由OptimisticForceIncrementLockingStrategy处理 public class OptimisticForceIncrementLockingStrategy implements LockingStrategy {//code omitted for brevityOverridepublic void lock(Serializable id, Object version, Object object, int timeout, SessionImplementor session) {if ( !lockable.isVersioned() ) {throw new HibernateException( [ lockMode ] not supported for non-versioned entities [ lockable.getEntityName() ] );}final EntityEntry entry session.getPersistenceContext().getEntry( object );// Register the EntityIncrementVersionProcess action to run just prior to transaction commit.( (EventSource) session ).getActionQueue().registerProcess( new EntityIncrementVersionProcess( object, entry ) );}
} 此策略在当前持久性上下文操作队列中注册EntityIncrementVersionProcess 。 在完成当前正在运行的事务之前锁定的实体版本会增加。 public class EntityIncrementVersionProcess implements BeforeTransactionCompletionProcess {//code omitted for brevityOverridepublic void doBeforeTransactionCompletion(SessionImplementor session) {final EntityPersister persister entry.getPersister();final Object nextVersion persister.forceVersionIncrement( entry.getId(), entry.getVersion(), session );entry.forceLocked( object, nextVersion );}
} 与OPTIMISTIC_FORCE_INCREMENT相似 PESSIMISTIC_FORCE_INCREMENT锁定模式由PessimisticForceIncrementLockingStrategy处理 public class PessimisticForceIncrementLockingStrategy implements LockingStrategy {//code omitted for brevityOverridepublic void lock(Serializable id, Object version, Object object, int timeout, SessionImplementor session) {if ( !lockable.isVersioned() ) {throw new HibernateException( [ lockMode ] not supported for non-versioned entities [ lockable.getEntityName() ] );}final EntityEntry entry session.getPersistenceContext().getEntry( object );final EntityPersister persister entry.getPersister();final Object nextVersion persister.forceVersionIncrement( entry.getId(), entry.getVersion(), session );entry.forceLocked( object, nextVersion );}
} 锁定的实体立即增加因此这两种锁定模式执行相同的逻辑但时间不同。 PESSIMISTIC_FORCE_INCREMENT的命名可能使您想到您正在使用悲观的锁定策略而实际上此锁定模式只是一个乐观的锁定变体。 悲观锁需要显式物理锁共享或独占而乐观锁则依赖于当前事务隔离级别的隐式锁。 存储库用例 我将重用之前的练习然后切换到使用PESSIMISTIC_FORCE_INCREMENT锁定模式。 回顾一下我们的域模型包含 一个存储库实体其版本随每次新的提交而增加 一个Commit实体封装了一个原子存储库状态转换 一个CommitChange组件封装了一个存储库资源更改 防止并行修改 爱丽丝和鲍勃同时访问我们的系统。 从数据库中获取存储库实体后它总是被锁定 private final CountDownLatch startLatch new CountDownLatch(1);
private final CountDownLatch endLatch new CountDownLatch(1);Test
public void testConcurrentPessimisticForceIncrementLockingWithLockWaiting() throws InterruptedException {LOGGER.info(Test Concurrent PESSIMISTIC_FORCE_INCREMENT Lock Mode With Lock Waiting);doInTransaction(new TransactionCallableVoid() {Overridepublic Void execute(Session session) {try {Repository repository (Repository) session.get(Repository.class, 1L);session.buildLockRequest(new LockOptions(LockMode.PESSIMISTIC_FORCE_INCREMENT)).lock(repository);executeNoWait(new CallableVoid() {Overridepublic Void call() throws Exception {return doInTransaction(new TransactionCallableVoid() {Overridepublic Void execute(Session _session) {LOGGER.info(Try to get the Repository row);startLatch.countDown();Repository _repository (Repository) _session.get(Repository.class, 1L);_session.buildLockRequest(new LockOptions(LockMode.PESSIMISTIC_FORCE_INCREMENT)).lock(_repository);Commit _commit new Commit(_repository);_commit.getChanges().add(new Change(index.html, 0a1,2...));_session.persist(_commit);_session.flush();endLatch.countDown();return null;}});}});startLatch.await();LOGGER.info(Sleep for 500ms to delay the other transaction PESSIMISTIC_FORCE_INCREMENT Lock Mode acquisition);Thread.sleep(500);Commit commit new Commit(repository);commit.getChanges().add(new Change(README.txt, 0a1,5...));commit.getChanges().add(new Change(web.xml, 17c17...));session.persist(commit);return null;} catch (InterruptedException e) {fail(Unexpected failure);}return null;}});endLatch.await();
} 该测试用例生成以下输出 #Alice selects the Repository
Query:{[select lockmodeop0_.id as id1_2_0_, lockmodeop0_.name as name2_2_0_, lockmodeop0_.version as version3_2_0_ from repository lockmodeop0_ where lockmodeop0_.id?][1]} #Alice locks the Repository using a PESSIMISTIC_FORCE_INCREMENT Lock Mode
Query:{[update repository set version? where id? and version?][1,1,0]} #Bob tries to get the Repository but the SELECT is blocked by Alice lock
INFO [pool-1-thread-1]: c.v.h.m.l.c.LockModePessimisticForceIncrementTest - Try to get the Repository row#Alice sleeps for 500ms to prove that Bob is waiting for her to release the acquired lock
Sleep for 500ms to delay the other transaction PESSIMISTIC_FORCE_INCREMENT Lock Mode acquisition#Alice makes two changes and inserts a new Commita hrefhttps://vladmihalcea.files.wordpress.com/2015/02/explicitlockingpessimisticforceincrementfailfast.pngimg srchttps://vladmihalcea.files.wordpress.com/2015/02/explicitlockingpessimisticforceincrementfailfast.png?w585 altExplicitLockingPessimisticForceIncrementFailFast width585 height224 classalignnone size-large wp-image-3955 //a
Query:{[insert into commit (id, repository_id) values (default, ?)][1]}
Query:{[insert into commit_change (commit_id, diff, path) values (?, ?, ?)][1,0a1,5...,README.txt]#The Repository version is bumped up to version 1 and a conflict is raised
Query:{[insert into commit_change (commit_id, diff, path) values (?, ?, ?)][1,17c17...,web.xml]} Query:{[update repository set version? where id? and version?][1,1,0]}#Alice commits the transaction, therefore releasing all locks
DEBUG [main]: o.h.e.t.i.j.JdbcTransaction - committed JDBC Connection#Bob Repository SELECT can proceed
Query:{[select lockmodepe0_.id as id1_2_0_, lockmodepe0_.name as name2_2_0_, lockmodepe0_.version as version3_2_0_ from repository lockmodepe0_ where lockmodepe0_.id?][1]} #Bob can insert his changes
Query:{[update repository set version? where id? and version?][2,1,1]}
Query:{[insert into commit (id, repository_id) values (default, ?)][1]}
Query:{[insert into commit_change (commit_id, diff, path) values (?, ?, ?)][2,0a1,2...,index.html]} 下图可以很容易地看到这个锁定过程 每当修改数据库行时 HSQLDB测试数据库“ 两阶段锁定”实现都会使用过程粒度表锁定。 这就是Bob不能获得Alice刚刚更新的Repository数据库行上的读取锁的原因。 其他数据库例如OraclePostgreSQL使用MVCC 因此允许SELECT继续执行使用当前的修改事务撤消日志来重新创建前一个行状态同时阻止冲突的数据修改语句例如当其他并发事务已经停止时更新存储库行尚未提交锁定的实体状态更改。 快速失败 即时版本增加具有一些有趣的好处 如果版本UPDATE成功获取了排他级锁则其他任何并发事务都无法修改锁定的数据库行。 这是将逻辑锁版本递增升级为物理锁数据库互斥锁的时刻。 如果版本UPDATE失败因为其他一些并发事务已经提交了版本更改那么我们当前正在运行的事务可以立即回滚而不是在提交期间等待事务失败 后一个用例可以如下所示 对于这种情况我们将使用以下测试用例 Test
public void testConcurrentPessimisticForceIncrementLockingFailFast() throws InterruptedException {LOGGER.info(Test Concurrent PESSIMISTIC_FORCE_INCREMENT Lock Mode fail fast);doInTransaction(new TransactionCallableVoid() {Overridepublic Void execute(Session session) {try {Repository repository (Repository) session.get(Repository.class, 1L);executeAndWait(new CallableVoid() {Overridepublic Void call() throws Exception {return doInTransaction(new TransactionCallableVoid() {Overridepublic Void execute(Session _session) {Repository _repository (Repository) _session.get(Repository.class, 1L);_session.buildLockRequest(new LockOptions(LockMode.PESSIMISTIC_FORCE_INCREMENT)).lock(_repository);Commit _commit new Commit(_repository);_commit.getChanges().add(new Change(index.html, 0a1,2...));_session.persist(_commit);_session.flush();return null;}});}});session.buildLockRequest(new LockOptions(LockMode.PESSIMISTIC_FORCE_INCREMENT)).lock(repository);fail(Should have thrown StaleObjectStateException!);} catch (StaleObjectStateException expected) {LOGGER.info(Failure: , expected);}return null;}});
} 生成以下输出 #Alice selects the Repository
Query:{[select lockmodeop0_.id as id1_2_0_, lockmodeop0_.name as name2_2_0_, lockmodeop0_.version as version3_2_0_ from repository lockmodeop0_ where lockmodeop0_.id?][1]} #Bob selects the Repository too
Query:{[select lockmodepe0_.id as id1_2_0_, lockmodepe0_.name as name2_2_0_, lockmodepe0_.version as version3_2_0_ from repository lockmodepe0_ where lockmodepe0_.id?][1]} #Bob locks the Repository using a PESSIMISTIC_FORCE_INCREMENT Lock Mode
Query:{[update repository set version? where id? and version?][1,1,0]} #Bob makes a change and inserts a new Commit
Query:{[insert into commit (id, repository_id) values (default, ?)][1]}
Query:{[insert into commit_change (commit_id, diff, path) values (?, ?, ?)][1,0a1,2...,index.html]} #Bob commits the transaction
DEBUG [pool-3-thread-1]: o.h.e.t.i.j.JdbcTransaction - committed JDBC Connection#Alice tries to lock the Repository
Query:{[update repository set version? where id? and version?][1,1,0]} #Alice cannot lock the Repository, because the version has changed
INFO [main]: c.v.h.m.l.c.LockModePessimisticForceIncrementTest - Failure:
org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.vladmihalcea.hibernate.masterclass.laboratory.concurrency.LockModePessimisticForceIncrementTest$Repository#1]结论 像OPTIMISTIC_FORCE_INCREMENT一样 PESSIMISTIC_FORCE_INCREMENT锁定模式对于将实体状态更改传播到父实体非常有用。 尽管锁定机制相似但是PESSIMISTIC_FORCE_INCREMENT可以当场应用从而允许当前运行的事务即时评估锁定结果。 代码可在GitHub上获得 。 翻译自: https://www.javacodegeeks.com/2015/02/hibernate-locking-patterns-pessimistic_force_increment-lock-mode-work.html
