| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.impl.store.raw.xact.RowLocking2 |
| 4 | |
| 5 | Copyright 1998, 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 2. |
| 41 | |
| 42 | The approach is to place all "write" container and row locks on the |
| 43 | transaction group lock list. Locks on this group will last until end |
| 44 | of transaction. All "read" container and row locks will be placed |
| 45 | on a group list, key'd by the ContainerId of the lock. Locks on this |
| 46 | list will either be released explicitly by the caller, or will be released |
| 47 | as a group when the unlockContainer() call is made. |
| 48 | |
| 49 | Note that write operations extend from the RowLocking3 implementations. |
| 50 | |
| 51 | @see org.apache.derby.iapi.store.raw.LockingPolicy |
| 52 | */ |
| 53 | public class RowLocking2 extends RowLockingRR |
| 54 | { |
| 55 | // no locking has no state, so it's safe to hold |
| 56 | // it as a static |
| 57 | private static final LockingPolicy NO_LOCK = new NoLocking(); |
| 58 | |
| 59 | protected RowLocking2(LockFactory lf) |
| 60 | { |
| 61 | super(lf); |
| 62 | } |
| 63 | |
| 64 | /** |
| 65 | * Obtain container level intent lock. |
| 66 | * <p> |
| 67 | * This implementation of row locking is 2 level, ie. table and row locking. |
| 68 | * It will interact correctly with tables opened with ContainerLocking3 |
| 69 | * locking mode. |
| 70 | * <p> |
| 71 | * Updater's will get table level IX locks, and X row locks. |
| 72 | * <p> |
| 73 | * Reader's will get table level IS locks, and S row locks. |
| 74 | * <p> |
| 75 | * Read locks are put in a separate "group" from the transaction, so that |
| 76 | * when the container is closed it can release these read locks. |
| 77 | * |
| 78 | * @param t Transaction to associate lock with. |
| 79 | * @param container Container to lock. |
| 80 | * @param waitForLock Should lock request wait until granted? |
| 81 | * @param forUpdate Should container be locked for update, or read? |
| 82 | * |
| 83 | * @return true if the lock was obtained, false if it wasn't. |
| 84 | * False should only be returned if the waitForLock policy was set to |
| 85 | * "false," and the lock was unavailable. |
| 86 | * |
| 87 | * @exception StandardException Standard exception policy. |
| 88 | **/ |
| 89 | public boolean lockContainer( |
| 90 | Transaction t, |
| 91 | ContainerHandle container, |
| 92 | boolean waitForLock, |
| 93 | boolean forUpdate) |
| 94 | throws StandardException |
| 95 | { |
| 96 | Object qualifier = forUpdate ? ContainerLock.CIX : ContainerLock.CIS; |
| 97 | |
| 98 | // for cursor stability put read locks on a separate lock chain, which |
| 99 | // will be released when the container is unlocked. |
| 100 | Object group = |
| 101 | forUpdate ? ((Object) t) : ((Object) container.getUniqueId()); |
| 102 | |
| 103 | boolean gotLock = |
| 104 | lf.lockObject( |
| 105 | t.getCompatibilitySpace(), group, container.getId(), qualifier, |
| 106 | waitForLock ? C_LockFactory.TIMED_WAIT : C_LockFactory.NO_WAIT); |
| 107 | |
| 108 | if (gotLock) |
| 109 | { |
| 110 | // look for covering table locks |
| 111 | // CIS and CIX is covered by CX |
| 112 | // In that case move the lock to the transaction list from the |
| 113 | // container list, as the null locking policy will do nothing in |
| 114 | // unlockContainer(). |
| 115 | // |
| 116 | |
| 117 | |
| 118 | if (lf.isLockHeld(t.getCompatibilitySpace(), t, container.getId(), |
| 119 | ContainerLock.CX)) |
| 120 | { |
| 121 | //release any container group locks becuase CX container lock will cover everthing. |
| 122 | lf.unlockGroup(t.getCompatibilitySpace(), container.getUniqueId()); |
| 123 | container.setLockingPolicy(NO_LOCK); |
| 124 | }else if ((!forUpdate) && |
| 125 | lf.isLockHeld(t.getCompatibilitySpace(), t, container.getId(), ContainerLock.CS)) |
| 126 | { |
| 127 | // move locks from container group to transaction group. |
| 128 | lf.transfer(t.getCompatibilitySpace(), group, t); |
| 129 | container.setLockingPolicy(NO_LOCK); |
| 130 | } |
| 131 | } |
| 132 | |
| 133 | return gotLock; |
| 134 | } |
| 135 | |
| 136 | |
| 137 | /** |
| 138 | * Obtain lock on record being read. |
| 139 | * <p> |
| 140 | * Assumes that a table level IS has been acquired. Will acquire a Shared |
| 141 | * or Update lock on the row, depending on the "forUpdate" parameter. |
| 142 | * <p> |
| 143 | * Read lock will be placed on separate group from transaction. |
| 144 | * |
| 145 | * @param t The transaction to associate the lock with. |
| 146 | * @param record The record to be locked. |
| 147 | * @param waitForLock Should lock request wait until granted? |
| 148 | * @param forUpdate Whether to open for read or write access. |
| 149 | * |
| 150 | * @return true if the lock was granted, false if waitForLock was false |
| 151 | * and the lock could not be granted. |
| 152 | * |
| 153 | * @exception StandardException Standard exception policy. |
| 154 | **/ |
| 155 | public boolean lockRecordForRead( |
| 156 | Transaction t, |
| 157 | ContainerHandle container_handle, |
| 158 | RecordHandle record, |
| 159 | boolean waitForLock, |
| 160 | boolean forUpdate) |
| 161 | throws StandardException |
| 162 | { |
| 163 | Object qualifier = forUpdate ? RowLock.RU2 : RowLock.RS2; |
| 164 | |
| 165 | return( |
| 166 | lf.lockObject( |
| 167 | t.getCompatibilitySpace(), |
| 168 | container_handle.getUniqueId(), |
| 169 | record, |
| 170 | qualifier, |
| 171 | waitForLock ? |
| 172 | C_LockFactory.TIMED_WAIT : C_LockFactory.NO_WAIT)); |
| 173 | } |
| 174 | |
| 175 | /** |
| 176 | * Obtain lock on record being read while holding a latch. |
| 177 | * <p> |
| 178 | * Assumes that a table level IS has been acquired. Will acquire a Shared |
| 179 | * or Update lock on the row, depending on the "forUpdate" parameter. |
| 180 | * <p> |
| 181 | * |
| 182 | * @param latch The latch being held. |
| 183 | * @param record The record to be locked. |
| 184 | * @param forUpdate Whether to open for read or write access. |
| 185 | * |
| 186 | * @exception StandardException Standard exception policy. |
| 187 | **/ |
| 188 | public void lockRecordForRead( |
| 189 | Latch latch, |
| 190 | RecordHandle record, |
| 191 | boolean forUpdate) |
| 192 | throws StandardException |
| 193 | { |
| 194 | // RESOLVE - Did I do the right thing with the "forUpdate" variable. |
| 195 | // RESOLVE (mikem) - looks like it needs work for update locks, and |
| 196 | // compatibility spaces. |
| 197 | |
| 198 | Object qualifier = forUpdate ? RowLock.RU2 : RowLock.RS2; |
| 199 | |
| 200 | lf.lockObject( |
| 201 | record.getContainerId(), record, qualifier, |
| 202 | C_LockFactory.TIMED_WAIT, latch); |
| 203 | } |
| 204 | |
| 205 | public void unlockRecordAfterRead( |
| 206 | Transaction t, |
| 207 | ContainerHandle container_handle, |
| 208 | RecordHandle record, |
| 209 | boolean forUpdate, |
| 210 | boolean row_qualified) |
| 211 | throws StandardException |
| 212 | { |
| 213 | Object qualifier = forUpdate ? RowLock.RU2 : RowLock.RS2; |
| 214 | |
| 215 | int count = |
| 216 | lf.unlock( |
| 217 | t.getCompatibilitySpace(), container_handle.getUniqueId(), |
| 218 | record, qualifier); |
| 219 | |
| 220 | if (SanityManager.DEBUG) |
| 221 | { |
| 222 | // in the case of lock escalation the count could be 0. |
| 223 | if (!(count == 1 || count == 0)) |
| 224 | { |
| 225 | SanityManager.THROWASSERT( |
| 226 | "count = " + count + |
| 227 | "record.getContainerId() = " + record.getContainerId()); |
| 228 | } |
| 229 | } |
| 230 | } |
| 231 | |
| 232 | /** |
| 233 | * Unlock read locks. |
| 234 | * <p> |
| 235 | * In Cursor stability release all read locks obtained. unlockContainer() |
| 236 | * will be called when the container is closed. |
| 237 | * <p> |
| 238 | * |
| 239 | * @param t The transaction to associate the lock with. |
| 240 | * @param container_handle Container to unlock. |
| 241 | **/ |
| 242 | public void unlockContainer( |
| 243 | Transaction t, |
| 244 | ContainerHandle container_handle) |
| 245 | { |
| 246 | // Only release read locks before end of transaction in level 2. |
| 247 | lf.unlockGroup( |
| 248 | t.getCompatibilitySpace(), container_handle.getUniqueId()); |
| 249 | } |
| 250 | } |