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| 33 | PointedEar | 1 | //$Id: LockModeType.java 11282 2007-03-14 22:05:59Z epbernard $ |
| 2 | package javax.persistence; |
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| 3 | |||
| 4 | /** |
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| 5 | * Lock modes that can be specified by means of the EntityManager.lock() method. |
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| 6 | * |
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| 7 | * The semantics of requesting locks of type LockModeType.READ and LockModeType.WRITE are t |
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| 8 | * he following. |
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| 9 | * |
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| 10 | * If transaction T1 calls lock(entity, LockModeType.READ) on a versioned object, the entity |
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| 11 | * manager must ensure that neither of the following phenomena can occur: |
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| 12 | * |
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| 13 | * * P1 (Dirty read): Transaction T1 modifies a row. Another transaction T2 then reads |
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| 14 | * that row and obtains the modified value, before T1 has committed or rolled back. |
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| 15 | * Transaction T2 eventually commits successfully; it does not matter whether T1 commits or rolls |
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| 16 | * back and whether it does so before or after T2 commits. |
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| 17 | * |
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| 18 | * * P2 (Non-repeatable read): Transaction T1 reads a row. Another transaction T2 then modifies |
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| 19 | * or deletes that row, before T1 has committed. Both transactions eventually commit successfully. |
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| 20 | * |
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| 21 | * Lock modes must always prevent the phenomena P1 and P2. |
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| 22 | * In addition, calling lock(entity, LockModeType.WRITE) on a versioned object, |
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| 23 | * will also force an update (increment) to the entity's version column. |
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| 24 | * |
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| 25 | * The persistence implementation is not required to support calling EntityManager.lock() |
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| 26 | * on a non-versioned object. When it cannot support a such lock call, it must |
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| 27 | * throw the PersistenceException. |
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| 28 | * |
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| 29 | * @author Emmanuel Bernard |
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| 30 | */ |
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| 31 | public enum LockModeType { |
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| 32 | /** |
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| 33 | * Read lock |
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| 34 | */ |
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| 35 | READ, |
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| 36 | /** |
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| 37 | * Write lock |
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| 38 | */ |
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| 39 | WRITE |
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| 40 | } |