RFR: JDK-8314194: Reusing CyclicBarrier, it should be possible to change the barrierCommand

[David Holmes]

On Thu, 31 Aug 2023 10:02:45 GMT, chenggwang <duke at openjdk.org> wrote:

>> Sorry, my description in Issue JDK-8314194(which I submitted) is ambiguous and makes you think of Phaser. My intention is that each generation of CyclicBarrier barrierCommand can change. Let me give you a scenario
>> For example, the U.S. Army 'Gordon Sullivan Cup'.
>> Five tanks competing.
>> 1. The first round is for artillery strikes against targets.
>> 2. Second round of anti-aircraft machine gun targets.
>> 3. The third round is minefield racing.
>> The scoring criteria are different for each round, so the CyclicBarrier's barrierCommand should be different for each round. But in the current code, `private final Runnable barrierCommand`, constructing the CyclicBarrier instance is already determined to be unchangeable.
>
>> As I wrote in the JBS issue and as Alan mentioned again above you can use the single `BarrierAction` object to track the state changes and count the generations/phase:
>> 
>> ```
>> Runnable barrierAction = new Runnable() {
>>   int phase = 0;
>>   public void run() {
>>     switch(phase++) {
>>       case 0: doArtillery(); break;
>>       case 1: doAntiAircraft(); nreak;
>>       case 2: doMinefield(); break;
>>     }
>>    void doArtillery() { ... }
>>    ...
>>   }
>> ```
>> 
>> I do not believe there is sufficient justification for expanding the `CyclicBarrier` API as proposed.
>> 
>> Happy to hear what @DougLea and @Martin-Buchholz think about this though.
> 
> Thank you @dholmes-ora @viktorklang-ora Your proposal is indeed a good solution! Enhancements and improvements became less urgent.

@chenggwang can you please close this PR and the associated Enhancement request. Thanks

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PR Comment: https://git.openjdk.org/jdk/pull/15239#issuecomment-1714854353