ibessonov commented on code in PR #4437: URL: https://github.com/apache/ignite-3/pull/4437#discussion_r1773258429
########## modules/page-memory/src/main/java/org/apache/ignite/internal/pagememory/persistence/checkpoint/CheckpointPageReplacement.java: ########## @@ -0,0 +1,136 @@ +/* + * 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.pagememory.persistence.checkpoint; + +import java.util.Set; +import java.util.concurrent.CompletableFuture; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.atomic.AtomicBoolean; +import org.apache.ignite.internal.pagememory.FullPageId; +import org.apache.ignite.internal.util.IgniteSpinBusyLock; +import org.jetbrains.annotations.Nullable; + +/** + * Helper class for synchronizing page replacement and the beginning of the fsync phase at a checkpoint. + * + * <p>For data consistency, it is important for us that page replacement occurs strictly before the beginning of the fsync phase.</p> + * + * <p>Usage:</p> + * <ul> + * <li>{@link #tryBlock(FullPageId)} - before you need to perform a page replacement.</li> + * <li>{@link #unblock(FullPageId, Throwable)} - after the page replacement has finished and written to disk. The method must be + * invoked even if any error occurred, so as not to hang a checkpoint.</li> + * <li>{@link #stopBlocking()} - must be invoked before the start of the fsync phase on the checkpoint and wait for the future to + * complete in order to safely perform the phase.</li> + * </ul> + * + * <p>Thread safe.</p> + */ +class CheckpointPageReplacement { + /** IDs of pages for which page replacement is in progress. */ + private final Set<FullPageId> pageIds = ConcurrentHashMap.newKeySet(); + + private final CompletableFuture<Void> stopBlockingFuture = new CompletableFuture<>(); + + private final IgniteSpinBusyLock busyLock = new IgniteSpinBusyLock(); + + private final AtomicBoolean stopGuard = new AtomicBoolean(); + + /** + * Tries to block the start of the fsync phase at a checkpoint before replacing the page. + * + * <p>It is expected that if the method returns {@code true}, it will not be invoked a second time with the same page ID.</p> + * + * @param pageId Page ID for which page replacement is expected to begin. + * @return {@code True} if the blocking was successful, {@code false} if the fsync phase is about to begin. + * @see #unblock(FullPageId, Throwable) + * @see #stopBlocking() + */ + boolean tryBlock(FullPageId pageId) { + if (!busyLock.enterBusy()) { + return false; + } + + try { + boolean added = pageIds.add(pageId); + + assert added : "Page is already in the process of being replaced: " + pageId; + + return true; + } finally { + busyLock.leaveBusy(); + } + } + + /** + * Unblocks the start of the fsync phase at a checkpoint after the page replacement is completed. + * + * <p>It is expected that the method will be invoked once and after the {@link #tryBlock(FullPageId)} returns {@code true} for same + * page ID.</p> + * + * <p>The fsync phase will only be started after page replacement has been completed for all pages for which + * {@link #tryBlock(FullPageId)} was invoked before {@link #stopBlocking()} was invoked, or no page replacement occurred at all.</p> + * + * <p>If any error occurred during page replacement, then the future from {@link #stopBlocking()} will be completed with the first + * error.</p> + * + * @param pageId Page ID for which the page replacement has ended. + * @param error Error on page replacement, {@code null} if missing. + * @see #tryBlock(FullPageId) + * @see #stopBlocking() + */ + void unblock(FullPageId pageId, @Nullable Throwable error) { + boolean removed = pageIds.remove(pageId); + + assert removed : "Replacement for the page either did not start or ended: " + pageId; + + if (error != null) { + stopBlockingFuture.completeExceptionally(error); + + return; + } + + if (!busyLock.enterBusy()) { + if (pageIds.isEmpty()) { + stopBlockingFuture.complete(null); + } + } else { + busyLock.leaveBusy(); + } + } + + /** + * Stops new blocks before the fsync phase starts at a checkpoint. + * + * @return Future that will be completed successfully if all blocks are completed before the current method is invoked, either if there + * were none, or with an error from the first unlock. + * @see #tryBlock(FullPageId) + * @see #unblock(FullPageId, Throwable) + */ + CompletableFuture<Void> stopBlocking() { + if (stopGuard.compareAndSet(false, true)) { Review Comment: I don't know, it's just a couple of lines of code, so if it stays here I won't be mad -- This is an automated message from the Apache Git Service. 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