Backport "HBASE-26765 Minor refactor of async scanning code (#4121)" to branch-2.5

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncConnectionImpl.java

@@ -340,7 +340,7 @@ public AsyncTableBuilder<ScanResultConsumer> getTableBuilder(TableName tableName
       public AsyncTable<ScanResultConsumer> build() {
         RawAsyncTableImpl rawTable =
           new RawAsyncTableImpl(AsyncConnectionImpl.this, RETRY_TIMER, this);
-        return new AsyncTableImpl(AsyncConnectionImpl.this, rawTable, pool);
+        return new AsyncTableImpl(rawTable, pool);
       }
     };
   }

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncTableImpl.java

@@ -43,12 +43,11 @@
 @InterfaceAudience.Private
 class AsyncTableImpl implements AsyncTable<ScanResultConsumer> {
 
-  private final AsyncTable<AdvancedScanResultConsumer> rawTable;
+  private final RawAsyncTableImpl rawTable;
 
   private final ExecutorService pool;
 
-  AsyncTableImpl(AsyncConnectionImpl conn, AsyncTable<AdvancedScanResultConsumer> rawTable,
-      ExecutorService pool) {
+  AsyncTableImpl(RawAsyncTableImpl rawTable, ExecutorService pool) {
     this.rawTable = rawTable;
     this.pool = pool;
   }

hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncTableResultScanner.java

@@ -23,23 +23,24 @@
 import java.io.InterruptedIOException;
 import java.util.ArrayDeque;
 import java.util.Queue;
+import org.apache.hadoop.hbase.TableName;
 import org.apache.hadoop.hbase.client.metrics.ScanMetrics;
 import org.apache.hadoop.hbase.util.FutureUtils;
 import org.apache.yetus.audience.InterfaceAudience;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * 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
+ * The {@link ResultScanner} implementation for {@link RawAsyncTableImpl}. 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, AdvancedScanResultConsumer {
 
   private static final Logger LOG = LoggerFactory.getLogger(AsyncTableResultScanner.class);
 
-  private final AsyncTable<AdvancedScanResultConsumer> rawTable;
+  private final TableName tableName;
 
   private final long maxCacheSize;
 
@@ -57,12 +58,10 @@ class AsyncTableResultScanner implements ResultScanner, AdvancedScanResultConsum
 
   private ScanResumer resumer;
 
-  public AsyncTableResultScanner(AsyncTable<AdvancedScanResultConsumer> table, Scan scan,
-      long maxCacheSize) {
-    this.rawTable = table;
+  public AsyncTableResultScanner(TableName tableName, Scan scan, long maxCacheSize) {
+    this.tableName = tableName;
     this.maxCacheSize = maxCacheSize;
     this.scan = scan;
-    table.scan(scan, this);
   }
 
   private void addToCache(Result result) {
@@ -72,9 +71,10 @@ private void addToCache(Result 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);
+      LOG.debug("{} stop prefetching when scanning {} as the cache size {}" +
+        " is greater than the maxCacheSize {}",
+        String.format("0x%x", System.identityHashCode(this)), tableName, cacheSize,
+        maxCacheSize);
     }
     resumer = controller.suspend();
   }
@@ -138,7 +138,7 @@ public synchronized Result next() throws IOException {
         return null;
       }
       if (error != null) {
-        FutureUtils.rethrow(error);
+        throw FutureUtils.rethrow(error);
       }
       try {
         wait();

hbase-client/src/main/java/org/apache/hadoop/hbase/client/RawAsyncTableImpl.java

@@ -666,10 +666,14 @@ private long resultSize2CacheSize(long maxResultSize) {
   }
 
   @Override
-  public ResultScanner getScanner(Scan scan) {
-    return new AsyncTableResultScanner(this, ReflectionUtils.newInstance(scan.getClass(), scan),
-      resultSize2CacheSize(
-        scan.getMaxResultSize() > 0 ? scan.getMaxResultSize() : defaultScannerMaxResultSize));
+  public AsyncTableResultScanner getScanner(Scan scan) {
+    final long maxCacheSize = resultSize2CacheSize(
+      scan.getMaxResultSize() > 0 ? scan.getMaxResultSize() : defaultScannerMaxResultSize);
+    final Scan scanCopy = ReflectionUtils.newInstance(scan.getClass(), scan);
+    final AsyncTableResultScanner scanner =
+      new AsyncTableResultScanner(tableName, scanCopy, maxCacheSize);
+    scan(scan, scanner);
+    return scanner;
   }
 
   @Override