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[SPARK-14930][SPARK-13693] Fix race condition in CheckpointWriter.stop() #12712

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[SPARK-14930][SPARK-13693] Fix race condition in CheckpointWriter.stop() #12712

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17 changes: 5 additions & 12 deletions streaming/src/main/scala/org/apache/spark/streaming/Checkpoint.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -184,8 +184,7 @@ class CheckpointWriter(
val executor = Executors.newFixedThreadPool(1)
val compressionCodec = CompressionCodec.createCodec(conf)
private var stopped = false
private var _fs: FileSystem = _

@volatile private[this] var fs: FileSystem = null
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@srowen srowen Apr 27, 2016

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Does this even need to be a member? it looks like it's used entirely in one method.

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@JoshRosen JoshRosen Apr 27, 2016

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It's actually referenced by inner classes. I think the idea here is that we'll avoid calling .getFileSystem too much by caching the result, but will have the ability to clear the cache in case the cached FileSystem seems to be in a bad state.

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@zsxwing zsxwing May 2, 2016

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minor: fs and latestCheckpointTime don't need to be volatile as we use Executors.newFixedThreadPool(1) here. We should also give the thread a name for better debugging.

@volatile private var latestCheckpointTime: Time = null

class CheckpointWriteHandler(
Expand All @@ -196,6 +195,9 @@ class CheckpointWriter(
if (latestCheckpointTime == null || latestCheckpointTime < checkpointTime) {
latestCheckpointTime = checkpointTime
}
if (fs == null) {
fs = new Path(checkpointDir).getFileSystem(hadoopConf)
}
var attempts = 0
val startTime = System.currentTimeMillis()
val tempFile = new Path(checkpointDir, "temp")
Expand Down Expand Up @@ -263,7 +265,7 @@ class CheckpointWriter(
case ioe: IOException =>
logWarning("Error in attempt " + attempts + " of writing checkpoint to "
+ checkpointFile, ioe)
reset()
fs = null
}
}
logWarning("Could not write checkpoint for time " + checkpointTime + " to file "
Expand Down Expand Up @@ -297,15 +299,6 @@ class CheckpointWriter(
", waited for " + (endTime - startTime) + " ms.")
stopped = true
}

private def fs = synchronized {
if (_fs == null) _fs = new Path(checkpointDir).getFileSystem(hadoopConf)
_fs
}

private def reset() = synchronized {
_fs = null
}
}


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