thetumbled commented on PR #18390:
URL: https://github.com/apache/pulsar/pull/18390#issuecomment-1310528449
> > In the `rehash` method, the member `this.table` of `Section` will be
reallocated a new long[] array, which is different from old table member.
> > ```
> > private void rehash(int newCapacity) {
> > long[] newTable = new long[4 * newCapacity];
> > ...
> > table = newTable;
> > ...
> > }
> > ```
>
> This inspires me. Can we fix the `get` issue in the same way?
>
> ```java
> boolean acquiredLock = false;
> // add local variable here, so OutOfBound won't happen
> long[] table = this.table;
> // calculate table.length / 4 as capacity to avoid rehash
changing capacity
> int bucket = signSafeMod(keyHash, table.length / 4);
>
> try {
> while (true) {
> long storedKey1 = table[bucket];
> long storedKey2 = table[bucket + 1];
> long storedValue1 = table[bucket + 2];
> long storedValue2 = table[bucket + 3];
>
> // compare table to ensure not rehash
> if (!acquiredLock && validate(stamp) && table ==
this.table) {
> if (key1 == storedKey1 && key2 == storedKey2) {
> return new LongPair(storedValue1,
storedValue2);
> } else if (storedKey1 == EmptyKey) {
> return null;
> }
> } else {
> if (!acquiredLock) {
> stamp = readLock();
> acquiredLock = true;
> // update local variable
> table = this.table;
> bucket = signSafeMod(keyHash, capacity);
> storedKey1 = table[bucket];
> storedKey2 = table[bucket + 1];
> storedValue1 = table[bucket + 2];
> storedValue2 = table[bucket + 3];
> }
> ```
It can also fix the bug. But is `&& table == this.table` indispensable? If
`table != this.table` ,there must be other thread acquire write lock and change
`this.table`, which make `validate(stamp)` return false.
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