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

[David Holmes]

On Fri, 11 Aug 2023 02:33:05 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.

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PR Comment: https://git.openjdk.org/jdk/pull/15239#issuecomment-1700472066