Shawyeok opened a new pull request, #25825:
URL: https://github.com/apache/pulsar/pull/25825
Fixes NPE in `IsolatedBookieEnsemblePlacementPolicy`
### Motivation
A `NullPointerException` occurs in `getExcludedBookiesWithIsolationGroups`
when `getIsolationGroup()` returns a `Pair` whose `left` value is `null`. This
happens when the `EnsemblePlacementPolicyConfig` carries a policy class name
that does not equal `IsolatedBookieEnsemblePlacementPolicy` — in that case the
`if` block that calls `pair.setLeft()` / `pair.setRight()` is skipped entirely,
leaving both sides of the `MutablePair` as `null`.
This bug was observed during the upgrade from the 2.8 branch to the 3.0
branch. The same defect may also exist in master.
**Full stack trace from production:**
```
2026-05-18T13:28:40.756Z [BookKeeperClientWorker-OrderedExecutor-35-0] ERROR
org.apache.bookkeeper.common.util.SingleThreadExecutor - Error while running
task: Cannot invoke "java.util.Set.contains(Object)" because the return value
of "org.apache.commons.lang3.tuple.Pair.getLeft()" is null
java.lang.NullPointerException: Cannot invoke
"java.util.Set.contains(Object)" because the return value of
"org.apache.commons.lang3.tuple.Pair.getLeft()" is null
at
org.apache.pulsar.bookie.rackawareness.IsolatedBookieEnsemblePlacementPolicy.getExcludedBookiesWithIsolationGroups(IsolatedBookieEnsemblePlacementPolicy.java:192)
at
org.apache.pulsar.bookie.rackawareness.IsolatedBookieEnsemblePlacementPolicy.getExcludedBookies(IsolatedBookieEnsemblePlacementPolicy.java:141)
at
org.apache.pulsar.bookie.rackawareness.IsolatedBookieEnsemblePlacementPolicy.replaceBookie(IsolatedBookieEnsemblePlacementPolicy.java:127)
at
org.apache.bookkeeper.client.BookieWatcherImpl.replaceBookie(BookieWatcherImpl.java:316)
at
org.apache.bookkeeper.client.EnsembleUtils.replaceBookiesInEnsemble(EnsembleUtils.java:69)
at
org.apache.bookkeeper.client.ReadOnlyLedgerHandle.handleBookieFailure(ReadOnlyLedgerHandle.java:222)
at
org.apache.bookkeeper.client.PendingAddOp.writeComplete(PendingAddOp.java:353)
at
org.apache.bookkeeper.proto.BookieClientImpl.completeAdd(BookieClientImpl.java:287)
at
org.apache.bookkeeper.proto.BookieClientImpl.access$200(BookieClientImpl.java:79)
at
org.apache.bookkeeper.proto.BookieClientImpl$ChannelReadyForAddEntryCallback.lambda$operationComplete$0(BookieClientImpl.java:405)
at
org.apache.bookkeeper.common.util.OrderedExecutor$TimedRunnable.run(OrderedExecutor.java:203)
at
org.apache.bookkeeper.common.util.SingleThreadExecutor.safeRunTask(SingleThreadExecutor.java:137)
at
org.apache.bookkeeper.common.util.SingleThreadExecutor.run(SingleThreadExecutor.java:107)
at
io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:840)
```
This error causes topics to time out during loading. Since there is no
automatic recovery path, the only way to restore service is by restarting the
broker.
### Modifications
Two complementary fixes:
1. **`getIsolationGroup()`**: Initialize `MutablePair` with empty sets as
defaults so the returned `Pair` always has non-null values, and remove the
now-redundant `else` branches that were explicitly setting the same empty sets.
2. **`getExcludedBookiesWithIsolationGroups()`** (defensive programming):
Resolve `primaryIsolationGroup` and `secondaryIsolationGroup` at the top of the
method using `ObjectUtils.getIfNull`, before any use. This eliminates both the
original NPE at the early-return `contains` check and a second latent NPE at
lines 218–219 where the pair values were previously assigned and dereferenced
without null guards.
### Verifying this change
- [ ] Make sure that the change passes the CI checks.
This change added tests and can be verified as follows:
- Added `testReplaceBookieWithNonMatchingPolicyClassShouldNotThrowNPE` to
reproduce the exact production failure: calling `replaceBookie` with custom
metadata whose `EnsemblePlacementPolicyConfig` policy class does not match
`IsolatedBookieEnsemblePlacementPolicy`, which previously caused the NPE.
### Does this pull request potentially affect one of the following parts:
- [ ] Dependencies (add or upgrade a dependency)
- [ ] The public API
- [ ] The schema
- [ ] The default values of configurations
- [ ] The threading model
- [ ] The binary protocol
- [ ] The REST endpoints
- [ ] The admin CLI options
- [ ] The metrics
- [ ] Anything that affects deployment
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