Java8之CompletableFuture async的理解

验证代码如下

ExecutorService executorService = Executors.newFixedThreadPool(3);

CompletableFuture a1 = CompletableFuture.supplyAsync(() -> {

logger.info("线程1{}{}","开始");

try {

        TimeUnit.MILLISECONDS.sleep(100);

}catch (InterruptedException e) {

        e.printStackTrace();

}

     logger.info("线程1{}{}","结束");

     return "1";

},executorService);

CompletableFuture a2 = CompletableFuture.supplyAsync(() -> {

logger.info("线程2{}{}","开始");

try {

      TimeUnit.MILLISECONDS.sleep(100);

}catch (InterruptedException e) {

      e.printStackTrace();

}

 logger.info("线程2{}{}","结束");

 return "1";

},executorService);

CompletableFuture a= a1.thenCombineAsync(a2,(s1,s2) -> {

  logger.info("组合线程{}{}");

  return  s1+s2;

},executorService);

Object result = a.get();

当executorService线程池大小为2时候,执行结果如下:

[pool-4-thread-1] INFO test.rcd.thread.CompletableFutureDemo.lambda$mains$4:127 - 组合线程{}{}

a1.thenCombineAsync方法始终被线程1或2执行,

当executorService线程池大小为3时候,执行结果如下:

[pool-4-thread-3] INFO test.rcd.thread.CompletableFutureDemo.lambda$mains$4:127 - 组合线程{}{}

a1.thenCombineAsync方法始终被线程3执行,

改为a1.thenCombine(),执行结果:

a1.thenCombineAsync方法始终被线程1或2执行,

由此可见,async方法始终尝试取新线程执行方法,不带async方法则会从当前线程里取线程执行.CompletableFuture似是与线程无关的.

欢迎指教