RFR: 8322149: ConcurrentHashMap smarter presizing for copy constructor and putAll [v3]

[ExE Boss]

On Thu, 18 Jan 2024 05:32:26 GMT, jmehrens <duke at openjdk.org> wrote:

>> Joshua Cao has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   putAll presize based on sum on both map sizes
>
> src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java line 1088:
> 
>> 1086:     public void putAll(Map<? extends K, ? extends V> m) {
>> 1087:         if (table != null) {
>> 1088:             tryPresize(size() + m.size());
> 
> Is overflow not an issue here because calling tryPresize with a negative value will invoke tableSizeFor?

When `tableSizeFor` is called with a negative value greater than `Integer.MIN_VALUE`, it’ll just return `+1`:
https://github.com/openjdk/jdk/blob/ff8cc268fdaaf85299c94088a226b73e7eaf6bdb/src/java.base/share/classes/java/util/concurrent/ConcurrentHashMap.java#L704-L707

This will in turn cause `tryPresize` to do nothing when `table` is already initialized.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/17116#discussion_r1457023596