java System.out 丢失

Question

以下简单代码的输出对我来说有点奇怪。它错过了在控制台上打印的 0 到 100 之间的一些数字。

谁能解释一下为什么省略打印？我对并发编程完全陌生。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

import org.junit.Test;


public class SimpleTest {

    @Test
    public void testSimple() throws Exception {
        ExecutorService executorService = Executors.newFixedThreadPool(10);

        for(int i = 0; i <= 100; i++) {
            executorService.execute(new SimpleRunnable(i));
        }

        executorService.shutdown();
    }

}

class SimpleRunnable implements Runnable {

    int i;

    public SimpleRunnable(int i) {
        this.i = i;
    }

    public void run() {
        synchronized(System.out) {
            System.out.println(i);
        }
    }

}

Answer 1

调用 shutdown 后应等待执行器服务完成

executorService.shutdown();
executor.awaitTermination(30, TimeUnit.SECONDS); // Wait for the tasks to finish.
// and flush!
System.out.flush();