java - 为什么这段代码没有触发ConcurrentModificationException？

Question

我正在从多个线程修改相同的列表，它不应该触发吗 迭代列表时出现 ConcurrentModificationException？

如何触发此异常？

public class ConcurrentTest {

    static List<String> list = setupList();

    public static List<String> setupList() {
        System.out.println("setup predefined list");

        List<String> l = new ArrayList();
        for(int i = 0; i < 50;i++) {
            l.add("test" + i);
        }

        return l;
    }

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(50);

        for(int i = 0; i < 50; i++) {
            executorService.submit( () -> {     
                list.add("key1");       

                Thread currentThread = Thread.currentThread();
                System.out.println( Thread.currentThread().getName() + ", " + list.size() );

                for(String val: list) {
                    try {
                        Thread.sleep(25);
                    }
                    catch(Exception e) {

                    }
                }

            });
        }

        executorService.shutdown();
    }
}

Answer 1

当您在迭代列表时修改列表时，会触发 ConcurrentModificationException。在您的代码中，当您迭代列表时，您只 hibernate 线程并且不修改它。这将触发异常:

for(String s: list) {
    list.add("something");
}