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

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Here is the source code for org.apache.hadoop.hbase.client.AsyncTableResultScanner.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.ConnectionUtils.calcEstimatedSize;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Throwables;

import java.io.IOException;
import java.io.InterruptedIOException;
import java.util.ArrayDeque;
import java.util.Queue;

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

/**
 * The {@link ResultScanner} implementation for {@link AsyncTable}. It will fetch data automatically
 * in background and cache it in memory. Typically the {@link #maxCacheSize} will be
 * {@code 2 * scan.getMaxResultSize()}.
 */
@InterfaceAudience.Private
class AsyncTableResultScanner implements ResultScanner, RawScanResultConsumer {

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

    private final RawAsyncTable rawTable;

    private final long maxCacheSize;

    private final Queue<Result> queue = new ArrayDeque<>();

    private long cacheSize;

    private boolean closed = false;

    private Throwable error;

    private ScanResumer resumer;

    public AsyncTableResultScanner(RawAsyncTable table, Scan scan, long maxCacheSize) {
        this.rawTable = table;
        this.maxCacheSize = maxCacheSize;
        table.scan(scan, this);
    }

    private void addToCache(Result result) {
        queue.add(result);
        cacheSize += calcEstimatedSize(result);
    }

    private void stopPrefetch(ScanController controller) {
        if (LOG.isDebugEnabled()) {
            LOG.debug(String.format("0x%x", System.identityHashCode(this)) + " stop prefetching when scanning "
                    + rawTable.getName() + " as the cache size " + cacheSize + " is greater than the maxCacheSize "
                    + maxCacheSize);
        }
        resumer = controller.suspend();
    }

    @Override
    public synchronized void onNext(Result[] results, ScanController controller) {
        assert results.length > 0;
        if (closed) {
            controller.terminate();
            return;
        }
        for (Result result : results) {
            addToCache(result);
        }
        notifyAll();
        if (cacheSize >= maxCacheSize) {
            stopPrefetch(controller);
        }
    }

    @Override
    public synchronized void onHeartbeat(ScanController controller) {
        if (closed) {
            controller.terminate();
        }
    }

    @Override
    public synchronized void onError(Throwable error) {
        this.error = error;
    }

    @Override
    public synchronized void onComplete() {
        closed = true;
        notifyAll();
    }

    private void resumePrefetch() {
        if (LOG.isDebugEnabled()) {
            LOG.debug(String.format("0x%x", System.identityHashCode(this)) + " resume prefetching");
        }
        resumer.resume();
        resumer = null;
    }

    @Override
    public synchronized Result next() throws IOException {
        while (queue.isEmpty()) {
            if (closed) {
                return null;
            }
            if (error != null) {
                Throwables.propagateIfPossible(error, IOException.class);
                throw new IOException(error);
            }
            try {
                wait();
            } catch (InterruptedException e) {
                throw new InterruptedIOException();
            }
        }
        Result result = queue.poll();
        cacheSize -= calcEstimatedSize(result);
        if (resumer != null && cacheSize <= maxCacheSize / 2) {
            resumePrefetch();
        }
        return result;
    }

    @Override
    public synchronized void close() {
        closed = true;
        queue.clear();
        cacheSize = 0;
        if (resumer != null) {
            resumePrefetch();
        }
        notifyAll();
    }

    @Override
    public boolean renewLease() {
        // we will do prefetching in the background and if there is no space we will just suspend the
        // scanner. The renew lease operation will be handled in the background.
        return false;
    }

    // used in tests to test whether the scanner has been suspended
    @VisibleForTesting
    synchronized boolean isSuspended() {
        return resumer != null;
    }
}