michaeljmarshall opened a new pull request, #4306:
URL: https://github.com/apache/bookkeeper/pull/4306
### Motivation
When tryOptimisticRead returns 0, the lock is acquired by another thread and
we will fail the validation step. We can therefore skip the eager cache
insertion.
Relevant javadocs from `StampedLock`:
```java
/**
* Returns a stamp that can later be validated, or zero
* if exclusively locked.
*
* @return a valid optimistic read stamp, or zero if exclusively locked
*/
public long tryOptimisticRead() {
long s;
return (((s = state) & WBIT) == 0L) ? (s & SBITS) : 0L;
}
/**
* Returns true if the lock has not been exclusively acquired
* since issuance of the given stamp. Always returns false if the
* stamp is zero. Always returns true if the stamp represents a
* currently held lock. Invoking this method with a value not
* obtained from {@link #tryOptimisticRead} or a locking method
* for this lock has no defined effect or result.
*
* @param stamp a stamp
* @return {@code true} if the lock has not been exclusively acquired
* since issuance of the given stamp; else false
*/
public boolean validate(long stamp) {
VarHandle.acquireFence();
return (stamp & SBITS) == (state & SBITS);
}
```
### Changes
Check for `stamp == 0` since it is a special case in the `StampedLock` class.
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