mkapalka commented on code in PR #2339: URL: https://github.com/apache/jackrabbit-oak/pull/2339#discussion_r2159143039
########## oak-jcr/src/main/java/org/apache/jackrabbit/oak/jcr/session/SessionSaveDelayer.java: ########## @@ -0,0 +1,146 @@ +/* + * 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.jackrabbit.oak.jcr.session; + +import static org.apache.jackrabbit.oak.spi.toggle.Feature.newFeature; + +import java.io.Closeable; +import java.util.concurrent.atomic.AtomicBoolean; + +import org.apache.jackrabbit.guava.common.base.Strings; +import org.apache.jackrabbit.oak.api.jmx.RepositoryManagementMBean; +import org.apache.jackrabbit.oak.spi.toggle.Feature; +import org.apache.jackrabbit.oak.spi.whiteboard.Whiteboard; +import org.apache.jackrabbit.oak.spi.whiteboard.WhiteboardUtils; +import org.jetbrains.annotations.NotNull; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * A delay mechanism for Session.save() operations. By default, Session.save + * calls are not delayed. If enabled, some of the save() operations can be + * delayed for a certain number of microseconds. + * + * This facility is enabled / disabled via feature toggle, and controlled via + * JMX bean, or (for testing) via two system properties. There is no attempt to + * control the delay, or which threads to delay, from within. It is meant for + * emergency situation, specially for cases where some threads write too much. + */ +public class SessionSaveDelayer implements Closeable { + + private static final Logger LOG = LoggerFactory.getLogger(SessionSaveDelayer.class); + + private static final String FT_SAVE_DELAY_NAME = "FT_SAVE_DELAY_OAK-11766"; + private static final String ENABLED_PROP_NAME = "oak.sessionSaveDelayer"; + private static final String CONFIG_PROP_NAME = "oak.sessionSaveDelayerConfig"; + + private final boolean enabledViaSysPropertey = Boolean.getBoolean(ENABLED_PROP_NAME); + private final String sysPropertyConfig = System.getProperty(CONFIG_PROP_NAME, ""); + private final Feature feature; + private final Whiteboard whiteboard; + private final AtomicBoolean closed = new AtomicBoolean(); + + private RepositoryManagementMBean cachedMbean; + private String lastConfigJson; + private SessionSaveDelayerConfig lastConfig; + private volatile boolean logNextDelay; + + public SessionSaveDelayer(@NotNull Whiteboard whiteboard) { + this.feature = newFeature(FT_SAVE_DELAY_NAME, whiteboard); + LOG.info("Initialized"); + if (enabledViaSysPropertey) { + LOG.info("Enabled via system property: " + ENABLED_PROP_NAME); + } + this.whiteboard = whiteboard; + } + + /** + * Gets the name of the current thread. + * + * @return the current thread name + */ + @NotNull + public static String getCurrentThreadName() { + return Thread.currentThread().getName(); + } + + private RepositoryManagementMBean getRepositoryMBean() { + if (cachedMbean == null) { + cachedMbean = WhiteboardUtils.getService(whiteboard, RepositoryManagementMBean.class); + } + return cachedMbean; + } + + public long delayIfNeeded() { Review Comment: Good point. I think that the disabled path is fine. The enabled path is a bit tricky though: since we access non-volatile fields from multiple threads without any synchronization, we have race conditions (according to the Java memory model). This might work fine but is hard to analyze. For example, if one thread sets `lastConfig` and another thread reads the new value, I'm not sure if we don't risk NPE accessing individual fields of the referenced object (since there was no safe publish of the object). IMHO, protecting the "enabled" path with a single lock, even a simple `synchronized { ... }` block, has less chance of introducing errors than unsafe access. -- 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. To unsubscribe, e-mail: oak-dev-unsubscr...@jackrabbit.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
