org.apache.hadoop.hbase.client.AsyncMetaRegionLocator.java Source code

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Here is the source code for org.apache.hadoop.hbase.client.AsyncMetaRegionLocator.java

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/**
 * 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.hadoop.hbase.client;

import static org.apache.hadoop.hbase.client.AsyncRegionLocator.*;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.atomic.AtomicReference;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.HRegionLocation;
import org.apache.hadoop.hbase.classification.InterfaceAudience;

/**
 * The asynchronous locator for meta region.
 */
@InterfaceAudience.Private
class AsyncMetaRegionLocator {

    private static final Log LOG = LogFactory.getLog(AsyncMetaRegionLocator.class);

    private final AsyncRegistry registry;

    private final AtomicReference<HRegionLocation> metaRegionLocation = new AtomicReference<>();

    private final AtomicReference<CompletableFuture<HRegionLocation>> metaRelocateFuture = new AtomicReference<>();

    AsyncMetaRegionLocator(AsyncRegistry registry) {
        this.registry = registry;
    }

    CompletableFuture<HRegionLocation> getRegionLocation() {
        for (;;) {
            HRegionLocation metaRegionLocation = this.metaRegionLocation.get();
            if (metaRegionLocation != null) {
                return CompletableFuture.completedFuture(metaRegionLocation);
            }
            if (LOG.isTraceEnabled()) {
                LOG.trace("Meta region location cache is null, try fetching from registry.");
            }
            if (metaRelocateFuture.compareAndSet(null, new CompletableFuture<>())) {
                if (LOG.isDebugEnabled()) {
                    LOG.debug("Start fetching meta region location from registry.");
                }
                CompletableFuture<HRegionLocation> future = metaRelocateFuture.get();
                registry.getMetaRegionLocation().whenComplete((locs, error) -> {
                    if (error != null) {
                        if (LOG.isDebugEnabled()) {
                            LOG.debug("Failed to fetch meta region location from registry", error);
                        }
                        metaRelocateFuture.getAndSet(null).completeExceptionally(error);
                        return;
                    }
                    HRegionLocation loc = locs.getDefaultRegionLocation();
                    if (LOG.isDebugEnabled()) {
                        LOG.debug("The fetched meta region location is " + loc);
                    }
                    // Here we update cache before reset future, so it is possible that someone can get a
                    // stale value. Consider this:
                    // 1. update cache
                    // 2. someone clear the cache and relocate again
                    // 3. the metaRelocateFuture is not null so the old future is used.
                    // 4. we clear metaRelocateFuture and complete the future in it with the value being
                    // cleared in step 2.
                    // But we do not think it is a big deal as it rarely happens, and even if it happens, the
                    // caller will retry again later, no correctness problems.
                    this.metaRegionLocation.set(loc);
                    metaRelocateFuture.set(null);
                    future.complete(loc);
                });
            } else {
                CompletableFuture<HRegionLocation> future = metaRelocateFuture.get();
                if (future != null) {
                    return future;
                }
            }
        }
    }

    void updateCachedLocation(HRegionLocation loc, Throwable exception) {
        updateCachedLoation(loc, exception, l -> metaRegionLocation.get(), newLoc -> {
            for (;;) {
                HRegionLocation oldLoc = metaRegionLocation.get();
                if (oldLoc != null && (oldLoc.getSeqNum() > newLoc.getSeqNum()
                        || oldLoc.getServerName().equals(newLoc.getServerName()))) {
                    return;
                }
                if (metaRegionLocation.compareAndSet(oldLoc, newLoc)) {
                    return;
                }
            }
        }, l -> {
            for (;;) {
                HRegionLocation oldLoc = metaRegionLocation.get();
                if (!canUpdate(l, oldLoc) || metaRegionLocation.compareAndSet(oldLoc, null)) {
                    return;
                }
            }
        });
    }

    void clearCache() {
        metaRegionLocation.set(null);
    }
}