http://www.avaje.org/persistence-api: Packaging parent for Avaje OSS projects.
  • Rob Bygrave 
/*
 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.  The Eclipse Public License is available
 * at http://www.eclipse.org/legal/epl-v10.html and the Eclipse Distribution License
 * is available at http://www.eclipse.org/org/documents/edl-v10.php.
 */
package javax.persistence;


Lock modes can be specified by means of passing a LockModeType argument to one of the EntityManager methods that take locks (lock, find, or
refresh) or to the Query.setLockMode() or TypedQuery.setLockMode() method. 

Lock modes can be used to specify either optimistic or pessimistic locks.

 Optimistic locks are specified using LockModeType.OPTIMISTIC and LockModeType.OPTIMISTIC_FORCE_INCREMENT. The lock mode type values LockModeType.READ and LockModeType.WRITE are synonyms of OPTIMISTIC and OPTIMISTIC_FORCE_INCREMENT respectively. The latter
are to be preferred for new applications.


The semantics of requesting locks of type LockModeType.OPTIMISTIC and
LockModeType.OPTIMISTIC_FORCE_INCREMENT are the following.




If transaction T1 calls for a lock of type LockModeType.OPTIMISTIC on a versioned object, the
entity manager must ensure that neither of the following phenomena can occur:

    

  • P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains
the modified value, before T1 has committed or rolled back. Transaction T2 eventually commits successfully;
it does not matter whether T1 commits or rolls back and whether it does so before or after T2 commits.
    • 

  • P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or
deletes that row, before T1 has committed. Both transactions eventually commit successfully. 
    • 




Lock modes must always prevent the phenomena P1 and P2.


In addition, calling a lock of type LockModeType.OPTIMISTIC_FORCE_INCREMENT on a versioned
object, will also force an update (increment) to the entity's version column.

 The persistence implementation is not required to support the use of optimistic lock modes on non-versioned objects. When it cannot support a such lock call, it must throw the PersistenceException. 
 The lock modes LockModeType.PESSIMISTIC_READ, LockModeType.PESSIMISTIC_WRITE, and LockModeType.PESSIMISTIC_FORCE_INCREMENT are used to immediately obtain long-term database locks. 

The semantics of requesting locks of type LockModeType.PESSIMISTIC_READ,
LockModeType.PESSIMISTIC_WRITE, and LockModeType.PESSIMISTIC_FORCE_INCREMENT are
the following.


If transaction T1 calls for a lock of type LockModeType.PESSIMISTIC_READ or
LockModeType.PESSIMISTIC_WRITE on an object, the entity manager must ensure that neither of
the following phenomena can occur:

    

  • P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains
the modified value, before T1 has committed or rolled back.
    • 

  • P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or deletes
that row, before T1 has committed or rolled back.
    • 




A lock with LockModeType.PESSIMISTIC_WRITE can be obtained on an entity instance to force
serialization among transactions attempting to update the entity data. A lock with
LockModeType.PESSIMISTIC_READ can be used to query data using repeatable-read semantics
without the need to reread the data at the end of the transaction to obtain a lock, and without blocking
other transactions reading the data. A lock with LockModeType.PESSIMISTIC_WRITE can be used
when querying data and there is a high likelihood of deadlock or update failure among concurrent updating
transactions.


The persistence implementation must support use of locks of type LockModeType.PESSIMISTIC_READ
LockModeType.PESSIMISTIC_WRITE on a non-versioned entity as well as on a versioned entity.

 When the lock cannot be obtained, and the database locking failure results in transaction-level rollback, the provider must throw the PessimisticLockException and ensure that the JTA transaction or EntityTransaction has been marked for rollback.

 When the lock cannot be obtained, and the database locking failure results in only statement-level rollback, the provider must throw the LockTimeoutException (and must not mark the transaction for rollback). 
Since:Java Persistence 1.0
/**
 * Lock modes can be specified by means of passing a <code>LockModeType</code> argument to one of the
 * {@link javax.persistence.EntityManager} methods that take locks (<code>lock</code>, <code>find</code>, or
 * <code>refresh</code>) or to the {@link Query#setLockMode Query.setLockMode()} or
 * {@link TypedQuery#setLockMode TypedQuery.setLockMode()} method.
 * <p>
 * Lock modes can be used to specify either optimistic or pessimistic locks.
 * <p>
 * Optimistic locks are specified using {@link LockModeType#OPTIMISTIC LockModeType.OPTIMISTIC} and
 * {@link LockModeType#OPTIMISTIC_FORCE_INCREMENT LockModeType.OPTIMISTIC_FORCE_INCREMENT}. The lock mode type
 * values {@link LockModeType#READ LockModeType.READ} and {@link LockModeType#WRITE LockModeType.WRITE} are
 * synonyms of <code>OPTIMISTIC</code> and <code>OPTIMISTIC_FORCE_INCREMENT</code> respectively. The latter
 * are to be preferred for new applications.
 * <p>
 * The semantics of requesting locks of type <code>LockModeType.OPTIMISTIC</code> and
 * <code>LockModeType.OPTIMISTIC_FORCE_INCREMENT</code> are the following.
 * <p>
 * <p>
 * If transaction T1 calls for a lock of type <code>LockModeType.OPTIMISTIC</code> on a versioned object, the
 * entity manager must ensure that neither of the following phenomena can occur:
 * <ul>
 * <li>P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains
 * the modified value, before T1 has committed or rolled back. Transaction T2 eventually commits successfully;
 * it does not matter whether T1 commits or rolls back and whether it does so before or after T2 commits.</li>
 * <li>P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or
 * deletes that row, before T1 has committed. Both transactions eventually commit successfully. </li>
 * </ul>
 * <p>
 * Lock modes must always prevent the phenomena P1 and P2.
 * <p>
 * In addition, calling a lock of type <code>LockModeType.OPTIMISTIC_FORCE_INCREMENT</code> on a versioned
 * object, will also force an update (increment) to the entity's version column.
 * <p>
 * The persistence implementation is not required to support the use of optimistic lock modes on non-versioned
 * objects. When it cannot support a such lock call, it must throw the {@link PersistenceException}.
 * <p>
 * The lock modes {@link LockModeType#PESSIMISTIC_READ LockModeType.PESSIMISTIC_READ},
 * {@link LockModeType#PESSIMISTIC_WRITE LockModeType.PESSIMISTIC_WRITE}, and
 * {@link LockModeType#PESSIMISTIC_FORCE_INCREMENT LockModeType.PESSIMISTIC_FORCE_INCREMENT} are used to
 * immediately obtain long-term database locks.
 * <p>
 * The semantics of requesting locks of type <code>LockModeType.PESSIMISTIC_READ</code>,
 * <code>LockModeType.PESSIMISTIC_WRITE</code>, and <code>LockModeType.PESSIMISTIC_FORCE_INCREMENT</code> are
 * the following.
 * <p>
 * If transaction T1 calls for a lock of type <code>LockModeType.PESSIMISTIC_READ</code> or
 * <code>LockModeType.PESSIMISTIC_WRITE</code> on an object, the entity manager must ensure that neither of
 * the following phenomena can occur:
 * <ul>
 * <li>P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads that row and obtains
 * the modified value, before T1 has committed or rolled back.</li>
 * <li>P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies or deletes
 * that row, before T1 has committed or rolled back.</li>
 * </ul>
 * <p>
 * A lock with <code>LockModeType.PESSIMISTIC_WRITE</code> can be obtained on an entity instance to force
 * serialization among transactions attempting to update the entity data. A lock with
 * <code>LockModeType.PESSIMISTIC_READ</code> can be used to query data using repeatable-read semantics
 * without the need to reread the data at the end of the transaction to obtain a lock, and without blocking
 * other transactions reading the data. A lock with <code>LockModeType.PESSIMISTIC_WRITE</code> can be used
 * when querying data and there is a high likelihood of deadlock or update failure among concurrent updating
 * transactions.
 * <p>
 * The persistence implementation must support use of locks of type <code>LockModeType.PESSIMISTIC_READ</code>
 * <code>LockModeType.PESSIMISTIC_WRITE</code> on a non-versioned entity as well as on a versioned entity.
 * <p>
 * When the lock cannot be obtained, and the database locking failure results in transaction-level rollback,
 * the provider must throw the {@link PessimisticLockException} and ensure that the JTA transaction or
 * <code>EntityTransaction</code> has been marked for rollback.
 * <p>
 * When the lock cannot be obtained, and the database locking failure results in only statement-level
 * rollback, the provider must throw the {@link LockTimeoutException} (and must not mark the transaction for
 * rollback).
 *
 * @since Java Persistence 1.0
 */
public enum LockModeType {
  
Synonymous with OPTIMISTIC. OPTIMISTIC is to be preferred for new
applications.

/**
   * Synonymous with <code>OPTIMISTIC</code>. <code>OPTIMISTIC</code> is to be preferred for new
   * applications.
   */
  READ,

  
Synonymous with OPTIMISTIC_FORCE_INCREMENT. OPTIMISTIC_FORCE_IMCREMENT is to
be preferred for new applications.

/**
   * Synonymous with <code>OPTIMISTIC_FORCE_INCREMENT</code>. <code>OPTIMISTIC_FORCE_IMCREMENT</code> is to
   * be preferred for new applications.
   */
  WRITE,

  
Optimistic lock.

Since:Java Persistence 2.0
/**
   * Optimistic lock.
   *
   * @since Java Persistence 2.0
   */
  OPTIMISTIC,

  
Optimistic lock, with version update.

Since:Java Persistence 2.0
/**
   * Optimistic lock, with version update.
   *
   * @since Java Persistence 2.0
   */
  OPTIMISTIC_FORCE_INCREMENT,

  
Pessimistic read lock.

Since:Java Persistence 2.0
/**
   * Pessimistic read lock.
   *
   * @since Java Persistence 2.0
   */
  PESSIMISTIC_READ,

  
Pessimistic write lock.

Since:Java Persistence 2.0
/**
   * Pessimistic write lock.
   *
   * @since Java Persistence 2.0
   */
  PESSIMISTIC_WRITE,

  
Pessimistic write lock, with version update.

Since:Java Persistence 2.0
/**
   * Pessimistic write lock, with version update.
   *
   * @since Java Persistence 2.0
   */
  PESSIMISTIC_FORCE_INCREMENT,

  
No lock.

Since:Java Persistence 2.0
/**
   * No lock.
   *
   * @since Java Persistence 2.0
   */
  NONE
}