java - 如何使手动重试线程安全

Question

我正在尝试手动重试。但我觉得代码不是线程安全的。任何人都可以提供有关如何使其线程安全的建议

while (retryCounter < maxRetries) {
          try {
            //TODO - add delay with config
            Thread.sleep(3000);
            t.run();
            break;
          } catch (Exception e) {
            retryCounter++;
            //TODO - Add audit logs
            if (retryCounter >= maxRetries) {
              LOG.info("Max retries exceeded");
              //TODO - remove exception add audit logs
              throw new RuntimeException("Max retry exceeded");
            }
          }
        }

提前致谢

Answer 1

正如 @ SteffenJacobs 所指出的，t.run 不会在单独的线程上执行运行逻辑，而是在进行调用的线程上执行。如果将 t.run 替换为 t.start，则运行逻辑将在不同的线程上异步执行，这意味着该新线程中的异常线程永远不会被您的 catch block 处理。例如下面的代码:

public static void main(String[] args) {
    int retryCounter = 0;
    int maxRetries = 3;

    Thread t = new Thread(new Runnable() {
        public void run() {
            System.out.println("..." + Thread.currentThread());
            throw new RuntimeException("Thrown by me!!!");
        }});

    while (retryCounter < maxRetries) {
        try {
            Thread.sleep(3000);
            System.out.println("***" + Thread.currentThread());
            t.start();
            break;
        } catch (Exception e) {
            System.out.println("retrying attempt " + retryCounter);
            System.out.println(e);
            retryCounter++;
            if (retryCounter >= maxRetries) {
                throw new RuntimeException("Max retry exceeded");
            }
        } finally {
            System.out.println("in finally");
        }
    }
}

打印:

***Thread[main,5,main]
in finally
...Thread[Thread-0,5,main]
Exception in thread "Thread-0" java.lang.RuntimeException: Thrown by me!!!
...
Process finished with exit code 0

底线 - 要检测线程任务中的错误，您需要考虑不同的方法。您可以考虑使用 Future ( https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/Future.html )。在这种情况下，您的任务将需要返回其执行状态，同时启动它们的代码等待 Future.get ，检查状态并根据需要重新运行任务。