alex-plekhanov commented on a change in pull request #8513: URL: https://github.com/apache/ignite/pull/8513#discussion_r555058028
########## File path: modules/core/src/main/java/org/apache/ignite/internal/processors/cache/persistence/pagemem/ClockPageReplacementFlags.java ########## @@ -0,0 +1,155 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.ignite.internal.processors.cache.persistence.pagemem; + +import java.util.function.LongUnaryOperator; +import org.apache.ignite.configuration.PageReplacementMode; +import org.apache.ignite.internal.util.GridUnsafe; + +/** + * Clock page replacement algorithm implementation. + * + * @see PageReplacementMode#CLOCK + */ +public class ClockPageReplacementFlags { + /** Total pages count. */ + private final int pagesCnt; + + /** Index of the next candidate ("hand"). */ + private volatile int curIdx; + + /** Pointer to memory region to store page hit flags. */ + private final long flagsPtr; + + /** + * @param totalPagesCnt Total pages count. + * @param memPtr Pointer to memory region. + */ + ClockPageReplacementFlags(int totalPagesCnt, long memPtr) { + pagesCnt = totalPagesCnt; + flagsPtr = memPtr; + + GridUnsafe.setMemory(flagsPtr, (totalPagesCnt + 7) >> 3, (byte)0); + } + + /** + * Find page to replace. + * + * @return Page index to replace. + */ + @SuppressWarnings("NonAtomicOperationOnVolatileField") + public int poll() { + // This method is always executed under exclusive lock, no other synchronization or CAS required. Review comment: We don't have the segment write lock in this class. I think it's not such a good idea to pass it and store it here only for assertion. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
