Technoboy- opened a new pull request #14433:
URL: https://github.com/apache/pulsar/pull/14433
Fixes #14413
### Motivation
When Retry topics are enabled, ConsumerBuilderImpl performs a
backwards-compatibility check to look for DLQ or Retry topics that were created
on previous version of Pulsar using a different naming scheme.
It does this by calling `getPartitionedTopicMetadata` and then using
`.get()` to block while waiting for the results
```java
if (client.getPartitionedTopicMetadata(oldRetryLetterTopic)
.get(client.conf.getOperationTimeoutMs(),
TimeUnit.MILLISECONDS).partitions > 0) {
retryLetterTopic = oldRetryLetterTopic;
}
if (client.getPartitionedTopicMetadata(oldDeadLetterTopic)
.get(client.conf.getOperationTimeoutMs(),
TimeUnit.MILLISECONDS).partitions > 0) {
deadLetterTopic = oldDeadLetterTopic;
}
```
This was implemented in https://github.com/apache/pulsar/pull/10129
A partial fix to add a Timeout was implemented in
https://github.com/apache/pulsar/pull/11597
However this fix does still block the calling thread during the lookup.
This can be an issue for code that attempt to call `subscribeAsync` on a
non-blocking Pool (such as when using Netty). The signature of `subscribeAsync`
implies that it's non-blocking. (And it seems somewhat pointless to have
`subscribeAsync` if it blocks anyway)
Note that this is an undocumented *breaking* change in behavior. Up until
2.9, it was safe to call this from a non-blocking pool.
In our case, we were running a custom SLF4J log exporter on the same thread
pool, which resulted in a *deadlock* when the number of concurrent
`subscribeAsync` calls exceeded the pool size. (This is probably an extreme
example and a poor decision on our part, but perhaps a good example of why
unexpected blocking can be dangerous)
Note that blocking call is still made even if the retry and DLQ names are
explicitly specified in DeadLetterPolicy. In that scenario the check should not
be needed. Aside from blocking the calling Thread, this also results in
unneeded lookup requests.
### Modifications
- Make retry and DLQ metadata async.
### Documentation
- [x] `no-need-doc`
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