Windows服务中的Timer Elapsed事件一一

Question

我在 C# 中创建 Windows 服务。我使用 timer elapsed 方法对数据库执行一些 CRUD 操作。例如

tmrAPACSEvent = new Timer(10000);
tmrAPACSEvent.Elapsed += new ElapsedEventHandler(tmrAPACSEvent_Elapsed);
tmrAPACSEvent.Enabled = true;

我在 OnStart 方法中创建了这个计时器，而 Event 是

private void tmrAPACSEvent_Elapsed(object sender, ElapsedEventArgs e)
{
    Library.WriteErrorLog("tmrAPACSEvent ticked and some job has been done successfully");

    try
    {
        var UnProcessedEvents = BLCustomService.GetCustomEvents();

        if (UnProcessedEvents != null)
        {
            foreach (EventData eventData in UnProcessedEvents)
            {
                Library.WriteErrorLog(BLCustomService.ChangeEventStatus(eventData).ToString());
                Library.WriteErrorLog(eventData.EventId.ToString());
                var ed = new EventData()
                {
                    dtRealDateTime = eventData.dtRealDateTime,
                    dwCardNumber = eventData.dwCardNumber,
                    strHolderName = eventData.strHolderName,
                    strInitObjName = eventData.strInitObjName
                };

                ed = BLCustomService.AddEvent(ed);
            }
            Library.WriteErrorLog("Events added");
        }
    }
    catch (Exception exception)
    {
        Library.WriteErrorLog("Error 96: " + exception.StackTrace);
    }
}

当我启动服务时，事件会并行执行，我会在数据库中获得多个对应“事件”的数据。我知道操作时间大于计时器经过时间。但我希望每个线程都必须等待在其之前启动的其他线程完成。

--可能的解决方案-- 我创建了全局静态布尔变量，然后将其赋值为 true。在我的事件中将其添加到 if 条件中，然后我将其分配为 false 直到 foreach 循环结束。

  private static bool adminForElapsedEvent = true;
    private void tmrAPACSEvent_Elapsed(object sender, ElapsedEventArgs e)
    {
        Library.WriteErrorLog("tmrAPACSEvent ticked and some job has been done successfully");

        try
        {
            var UnProcessedEvents = BLCustomService.GetCustomEvents();

            //Library.WriteErrorLog("tmrAPACSEvent ticked and some job has been done successfully" + UnProcessedEvents.Count);
            if (UnProcessedEvents != null || adminForElapsedEvent)
            {
                adminForElapsedEvent = false;

                // doing some wordks
                adminForElapsedEvent = true;
            }
        }
        catch (Exception exception)
        {
            Library.WriteErrorLog("Error 96: " + exception.StackTrace);
        }
    }

此方法第一次有效，但几分钟后 Elapse 事件再次运行，并重复插入。

Answer 1

您可以尝试的第一件事：设置您的 tmrAPACSEvent.Enabled = false 而不是 adminForElapsedEvent = false;。那么你甚至不需要全局变量。

这不是万无一失的，因为您遇到了竞争条件。因此，下一个建议是锁定您的代码。但是不要使用普通锁，使用Mutex 我发现它可以提供更好的资源访问控制。所以你的代码现在看起来像这样：

// Create a new Mutex. The creating thread does not own the mutex.
private static Mutex mux = new Mutex();

private void tmrAPACSEvent_Elapsed(object sender, ElapsedEventArgs e)
{
    Library.WriteErrorLog("tmrAPACSEvent ticked and some job has been done successfully");

    try
    {
        var UnProcessedEvents = BLCustomService.GetCustomEvents();

        if (UnProcessedEvents != null)
        {
            tmrAPACSEvent.Enabled = false;

            // Wait until it is safe to enter, and do not enter if the request times out.
            if (mux.WaitOne(7000))
            {
                // do work

                // note this is inside the mutex so that the timer is guaranteed enabled, even for just a moment
                tmrAPACSEvent.Enabled = true;
            }
        }
    }
    catch (Exception exception)
    {
        Library.WriteErrorLog("Error 96: " + exception.StackTrace);
    }
}