问题：ThreadPoolExecutor提交过多会报RejectedExecutionException
```
public class executor { public static void main(String[] args) {// ExecutorService executorService = Executors.newFixedThreadPool(6);// ExecutorService executorService = Executors.newCachedThreadPool(); ExecutorService executorService = new ThreadPoolExecutor(4, 8, 60L, TimeUnit.SECONDS, new SynchronousQueue<>()); for (int i = 0; i < 10; i++) { String name = Integer.toString(i); executorService.submit(() -> { System.out.println("start task " + name); try { Thread.sleep(1000); } catch (InterruptedException e) { } System.out.println("end task " + name); }); } executorService.shutdown(); }}
```
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