slfan1989 commented on PR #4367:
URL: https://github.com/apache/hadoop/pull/4367#issuecomment-1152828770
@Hexiaoqiao @ZanderXu @tomscut
I still have some doubts about this.
1. I still hope ZanderXu Can provide deadlock exception stack error
information, I will continue to try to reproduce this problem in this part.
2. I read the code of testSynchronousEviction carefully, this code uses the
special storage strategy LAZY_PERSIST, This strategy will asynchronously flush
memory blocks to disk. LazyWriter takes care of this work.
Part of the code is as follows
```
private boolean saveNextReplica() {
RamDiskReplica block = null;
FsVolumeReference targetReference;
FsVolumeImpl targetVolume;
ReplicaInfo replicaInfo;
boolean succeeded = false;
try {
block = ramDiskReplicaTracker.dequeueNextReplicaToPersist();
if (block != null) {
try (AutoCloseableLock lock =
lockManager.writeLock(LockLevel.BLOCK_POOl,
block.getBlockPoolId())) {
replicaInfo = volumeMap.get(block.getBlockPoolId(),
block.getBlockId());
.....
```
If ZanderXu's judgment is correct, will this code also deadlock?
3.I always have a question, why we first add blockpool readlock, and then
add volume write lock, how is the order of this lock derived?
4.I checked lockManager.writeLock(LockLevel.BLOCK_POOl,
block.getBlockPoolId()), and I found that when adding volume, the writeLock of
BLOCK_POOl is also used, so will it also deadlock?
> in conclusion
I don't think this is a deadlock. Is it because createRow got the read lock,
which caused evictBlocks to get the write lock for a long time, and then
exceeded the waiting time of the junit test, which eventually led to an error.
I think to solve this problem completely, we also need to look at the
processing logic of LazyWriter. It should not be enough to just modify
evictBlocks.
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