| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.impl.store.raw.xact.RowLocking1 |
| 4 | |
| 5 | Copyright 1999, 2004 The Apache Software Foundation or its licensors, as applicable. |
| 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | you may not use this file except in compliance with the License. |
| 9 | You may obtain a copy of the License at |
| 10 | |
| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | See the License for the specific language governing permissions and |
| 17 | limitations under the License. |
| 18 | |
| 19 | */ |
| 20 | |
| 21 | package org.apache.derby.impl.store.raw.xact; |
| 22 | |
| 23 | import org.apache.derby.iapi.services.locks.LockFactory; |
| 24 | import org.apache.derby.iapi.services.locks.C_LockFactory; |
| 25 | import org.apache.derby.iapi.services.locks.Latch; |
| 26 | |
| 27 | import org.apache.derby.iapi.services.sanity.SanityManager; |
| 28 | |
| 29 | import org.apache.derby.iapi.store.raw.ContainerHandle; |
| 30 | import org.apache.derby.iapi.store.raw.ContainerLock; |
| 31 | import org.apache.derby.iapi.store.raw.LockingPolicy; |
| 32 | import org.apache.derby.iapi.store.raw.RecordHandle; |
| 33 | import org.apache.derby.iapi.store.raw.RowLock; |
| 34 | import org.apache.derby.iapi.store.raw.Transaction; |
| 35 | |
| 36 | import org.apache.derby.iapi.error.StandardException; |
| 37 | |
| 38 | |
| 39 | /** |
| 40 | A locking policy that implements row level locking with isolation degree 1. |
| 41 | |
| 42 | This is an implementation of Gray's degree 1 isolation, read uncommitted, |
| 43 | or often referred to as dirty reads. Basically read operations are |
| 44 | done with no locking. |
| 45 | |
| 46 | This locking policy is only to be used for read operations. |
| 47 | |
| 48 | The approach is to place all "write" container and row locks on the |
| 49 | transaction group lock list. Locks on this group will last until end |
| 50 | of transaction. |
| 51 | |
| 52 | This implementation will still get table level intent locks. This is to |
| 53 | prevent hard cases where the container otherwise could be deleted while |
| 54 | read uncommitted reader is still accessing it. In order to not get table |
| 55 | level intent locks some sort of other ddl level lock would have to be |
| 56 | implemented. |
| 57 | |
| 58 | All "read" row locks will be not be requested. |
| 59 | |
| 60 | Note that write operations extend from the RowLocking3 implementations. |
| 61 | |
| 62 | @see org.apache.derby.iapi.store.raw.LockingPolicy |
| 63 | */ |
| 64 | public class RowLocking1 extends RowLocking2 |
| 65 | { |
| 66 | |
| 67 | protected RowLocking1(LockFactory lf) |
| 68 | { |
| 69 | super(lf); |
| 70 | } |
| 71 | |
| 72 | /** |
| 73 | * Obtain lock on record being read. |
| 74 | * <p> |
| 75 | * Assumes that a table level IS has been acquired. Will acquire a Shared |
| 76 | * or Update lock on the row, depending on the "forUpdate" parameter. |
| 77 | * <p> |
| 78 | * Read lock will be placed on separate group from transaction. |
| 79 | * |
| 80 | * @param t The transaction to associate the lock with. |
| 81 | * @param record The record to be locked. |
| 82 | * @param waitForLock Should lock request wait until granted? |
| 83 | * @param forUpdate Whether to open for read or write access. |
| 84 | * |
| 85 | * @return true if the lock was granted, false if waitForLock was false |
| 86 | * and the lock could not be granted. |
| 87 | * |
| 88 | * @exception StandardException Standard exception policy. |
| 89 | **/ |
| 90 | public boolean lockRecordForRead( |
| 91 | Transaction t, |
| 92 | ContainerHandle container_handle, |
| 93 | RecordHandle record, |
| 94 | boolean waitForLock, |
| 95 | boolean forUpdate) |
| 96 | throws StandardException |
| 97 | { |
| 98 | |
| 99 | return( |
| 100 | !forUpdate ? |
| 101 | true : |
| 102 | super.lockRecordForRead( |
| 103 | t, container_handle, record, waitForLock, forUpdate)); |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * Obtain lock on record being read while holding a latch. |
| 108 | * <p> |
| 109 | * Assumes that a table level IS has been acquired. Will acquire a Shared |
| 110 | * or Update lock on the row, depending on the "forUpdate" parameter. |
| 111 | * <p> |
| 112 | * |
| 113 | * @param latch The latch being held. |
| 114 | * @param record The record to be locked. |
| 115 | * @param forUpdate Whether to open for read or write access. |
| 116 | * |
| 117 | * @exception StandardException Standard exception policy. |
| 118 | **/ |
| 119 | public void lockRecordForRead( |
| 120 | Latch latch, |
| 121 | RecordHandle record, |
| 122 | boolean forUpdate) |
| 123 | throws StandardException |
| 124 | { |
| 125 | if (forUpdate) |
| 126 | super.lockRecordForRead(latch, record, forUpdate); |
| 127 | } |
| 128 | |
| 129 | public void unlockRecordAfterRead( |
| 130 | Transaction t, |
| 131 | ContainerHandle container_handle, |
| 132 | RecordHandle record, |
| 133 | boolean forUpdate, |
| 134 | boolean row_qualified) |
| 135 | throws StandardException |
| 136 | { |
| 137 | if (forUpdate) |
| 138 | { |
| 139 | super.unlockRecordAfterRead( |
| 140 | t, container_handle, record, forUpdate, row_qualified); |
| 141 | } |
| 142 | return; |
| 143 | } |
| 144 | } |