java - 为什么 BoundedExecutor 必须捕获 RejectedExecutionException？

Question

《Java并发实践》一书中的BoundedExecutor，任务提交已经被信号量限制了。底层执行器什么时候会抛出RejectedExecutionException？也许当操作系统耗尽线程时？

public class BoundedExecutor {
  private final Executor exec;
  private final Semaphore semaphore;

  public BoundedExecutor(Executor exec, int bound) {
    this.exec = exec;
    this.semaphore = new Semaphore(bound);
  }

  public void submitTask(final Runnable command) throws InterruptedException, RejectedExecutionException 
  {
    semaphore.acquire();

    try {
        exec.execute(new Runnable() {
            @Override public void run() {
                try {
                    command.run();
                } finally {
                    semaphore.release();
                }
            }
        });
    } catch (RejectedExecutionException e) {
        semaphore.release();
        throw e;
    }
  }
}

Answer 1

Executor.execute()契约(Contract)的一部分是它可以抛出 RejectedExecutionException :

if this task cannot be accepted for execution

这对于任何给定的 Executor 实现意味着什么取决于该实现的判断。我可以创建一个 OnlyOnSundaysExecutor 来拒绝任务，除非一周中的当天是星期日。您必须检查各种 Executor 实现的文档，以了解它们在什么情况下会抛出 RejectedExecutionException 异常。