SincereXIA commented on a change in pull request #616:
URL: https://github.com/apache/ratis/pull/616#discussion_r821450785
##########
File path:
ratis-server/src/main/java/org/apache/ratis/server/raftlog/segmented/SegmentedRaftLogOutputStream.java
##########
@@ -67,7 +67,9 @@ public SegmentedRaftLogOutputStream(File file, boolean
append, long segmentMaxSi
// write header
preallocateIfNecessary(SegmentedRaftLogFormat.getHeaderLength());
SegmentedRaftLogFormat.applyHeaderTo(CheckedConsumer.asCheckedFunction(out::write));
- out.flush();
+ synchronized (out) {
+ out.flush();
Review comment:
We found errors like this during testing:
```
2022-03-08 11:15:23,856
[97cb3f28-f298-4ed3-93c7-3be44bfe8b7b@group-892C7CF01088-SegmentedRaftLogWorker]
ERROR org.apache.ratis.server.raftlog.segmented.SegmentedRaftLogWorker:
97cb3f28-f298-4ed3-93c7-3be44bfe8b7b@group-892C7CF01088-SegmentedRaftLogWorker
hit exception
java.lang.IllegalArgumentException
at java.nio.Buffer.position(Buffer.java:244)
at java.nio.DirectByteBuffer.put(DirectByteBuffer.java:377)
at
org.apache.ratis.server.raftlog.segmented.BufferedWriteChannel.write(BufferedWriteChannel.java:61)
at
org.apache.ratis.server.raftlog.segmented.SegmentedRaftLogOutputStream.write(SegmentedRaftLogOutputStream.java:100)
at
org.apache.ratis.server.raftlog.segmented.SegmentedRaftLogWorker$WriteLog.execute(SegmentedRaftLogWorker.java:610)
at
org.apache.ratis.server.raftlog.segmented.SegmentedRaftLogWorker.run(SegmentedRaftLogWorker.java:404)
at java.lang.Thread.run(Thread.java:748)
2022-03-08 11:15:23,858
[97cb3f28-f298-4ed3-93c7-3be44bfe8b7b@group-892C7CF01088-SegmentedRaftLogWorker]
INFO org.apache.ratis.server.RaftServer$Division:
97cb3f28-f298-4ed3-93c7-3be44bfe8b7b@group-892C7CF01088: shutdown
```
I think the cause of this error is that class `BufferedWriteChannel` is not
thread safe, but an asynchronous flush may operate on this object at the same
time as the main thread.
```
/**
* Provides a buffering layer in front of a FileChannel for writing.
*
* This class is NOT threadsafe.
*/
class BufferedWriteChannel implements Closeable {
````
After we make it synchronized, the error no longer occurs.
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