java - 如何同步 jBatch 执行？

Question

我正在用 jBeret 编写一个 jBatch 程序。我目前就是这样做的。

final JobOperator operator = BatchRuntime.getJobOperator();
logger.debug("operator: {}", operator);

final long id = operator.start("some", null);
logger.debug("id: {}", id);

final JobExecution execution = operator.getJobExecution(id);
logger.debug("execution: {}", execution);

问题是执行似乎是异步运行的，主要方法只是返回。

我能做的最好的事情就是循环直到退出状态不为空。

String status;
while ((status = execution.getExitStatus()) == null) {
    //logger.debug("sleeping");
    Thread.sleep(1000L);
}
logger.debug("status: {}", status);

还有其他方法吗？

Answer 1

如果您需要block-and-wait，正如您所描述的，没有其他选择，但可以实现类似awaiCompletion() 的功能。

您的循环方法可以改进。我们以 ThreadPoolExecutor 为例。它有以下方法:

    /**
     * Blocks until all tasks have completed execution after a shutdown
     * request, or the timeout occurs, or the current thread is
     * interrupted, whichever happens first.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return {@code true} if this executor terminated and
     *         {@code false} if the timeout elapsed before termination
     * @throws InterruptedException if interrupted while waiting
     */
    boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException;

这里是实现:

    public boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException {
        long nanos = unit.toNanos(timeout);
        final ReentrantLock mainLock = this.mainLock;
        mainLock.lock();
        try {
            for (;;) {
                if (runStateAtLeast(ctl.get(), TERMINATED))
                    return true;
                if (nanos <= 0)
                    return false;
                nanos = termination.awaitNanos(nanos);
            }
        } finally {
            mainLock.unlock();
        }
    }

请注意:

• 无限循环应该总是定义退出条件
• 在你的情况下超时是必须的，因为你不太可能准备好无休止的等待
• 当然你必须知道是超时还是工作终止

所以，这是一个改编版本:

    public static boolean awaitTermination(JobExecution execution, long timeout) throws InterruptedException {
        final long limit = System.currentTimeMillis() + timeout;
        for (;;) {
            if (null != execution.getExitStatus()) {
                return true;
            }

            if (System.currentTimeMillis() >= limit) {
                return false;
            }

            Thread.sleep(timeout/10);            
        }
    }