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HDFS-10182. Hedged read might overwrite user's buf. Contributed by zhouyingchao. 

(cherry picked from commit d8383c687c)
This commit is contained in:
Walter Su 2016-03-28 15:44:25 +08:00
parent 2b1f066d2d
commit 07b0abe0b3
1 changed files with 7 additions and 9 deletions
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16
hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java
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@ -1329,7 +1329,7 @@ public class DFSInputStream extends FSInputStream
// chooseDataNode is a commitment. If no node, we go to
// the NN to reget block locations. Only go here on first read.
chosenNode = chooseDataNode(block, ignored);
bb = ByteBuffer.wrap(buf, offset, len);
bb = ByteBuffer.allocate(len);
Callable<ByteBuffer> getFromDataNodeCallable = getFromOneDataNode(
chosenNode, block, start, end, bb,
corruptedBlockMap, hedgedReadId++);
@ -1340,7 +1340,9 @@ public class DFSInputStream extends FSInputStream
Future<ByteBuffer> future = hedgedService.poll(
conf.getHedgedReadThresholdMillis(), TimeUnit.MILLISECONDS);
if (future != null) {
future.get();
ByteBuffer result = future.get();
System.arraycopy(result.array(), result.position(), buf, offset,
len);
return;
}
DFSClient.LOG.debug("Waited {}ms to read from {}; spawning hedged "
@ -1378,13 +1380,9 @@ public class DFSInputStream extends FSInputStream
ByteBuffer result = getFirstToComplete(hedgedService, futures);
// cancel the rest.
cancelAll(futures);
if (result.array() != buf) { // compare the array pointers
dfsClient.getHedgedReadMetrics().incHedgedReadWins();
System.arraycopy(result.array(), result.position(), buf, offset,
len);
} else {
dfsClient.getHedgedReadMetrics().incHedgedReadOps();
}
dfsClient.getHedgedReadMetrics().incHedgedReadWins();
System.arraycopy(result.array(), result.position(), buf, offset,
len);
return;
} catch (InterruptedException ie) {
// Ignore and retry