RFR: 8355726: LinkedBlockingDeque fixes and improvements

[Viktor Klang]

On Thu, 8 May 2025 13:47:41 GMT, kabutz <duke at openjdk.org> wrote:

>> src/java.base/share/classes/java/util/concurrent/LinkedBlockingDeque.java line 341:
>> 
>>> 339:             if (count >= capacity)
>>> 340:                 return false;
>>> 341:             linkFirst(node);
>> 
>> I'm a bit uneasy about incrementing the `count` in `linkFirst` but not enforcing the invariant. What's the benefit to changing linkFirst and linkLast to return void instead of keeping the original returning a boolean?
>
>> I'm a bit uneasy about incrementing the `count` in `linkFirst` but not enforcing the invariant. What's the benefit to changing linkFirst and linkLast to return void instead of keeping the original returning a boolean?
> 
> I based the approach on the LBQ enqueue() and dequeue() methods, which also return void and have a comment with the assertion.

@kabutz I'd think maintaining the invariants within linkFirst and linkLast would be preferable (`count` must be re-read under the lock anyway)

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PR Review Comment: https://git.openjdk.org/jdk/pull/24925#discussion_r2135364751