基於 Quartz.NET 實現可中斷的任務

基於 Quartz.NET 實現可中斷的任務

Quartz.NET 是一個開源的作業調度框架，非常適合在平時的工作中，定時輪詢資料庫同步，定時郵件通知，定時處理數據等。 Quartz.NET 允許開發人員根據時間間隔（或天）來調度作業。它實現了作業和觸發器的多對多關係，還能把多個作業與不同的觸發器關聯。整合了 Quartz.NET 的應用程式可以重用來自不同事件的作業，還可以為一個事件組合多個作業。 在 Quartz.NET 的預設實現中 Worker 並非後臺線程（ IsBackground= false ），所以當我們終止調度器（調用 Scheduler.Shutdown() 方法）時，假如有一個比較耗時的 Job 正在執行，那麼進程將不會立即結束，而是等待這個 Job 執行完畢再結束。

為了可以立即退出進程，我們需要瞭解一個 Quartz.NET 中內置的介面 ： IInterruptableJob 。該介面表示一個可中斷的任務，實現該介面的 Job 被認為是可以被中斷執行的，下麵是官方對 IInterruptableJob 介面的定義和解釋：

The interface to be implemented by Quartz.IJobs that provide a mechanism for having their execution interrupted. It is NOT a requirement for jobs to implement this interface - in fact, for most people, none of their jobs will. The means of actually interrupting the Job must be implemented within the Quartz.IJob itself (the Quartz.IInterruptableJob.Interrupt method of this interface is simply a means for the scheduler to inform the Quartz.IJob that a request has been made for it to be interrupted). The mechanism that your jobs use to interrupt themselves might vary between implementations. However the principle idea in any implementation should be to have the body of the job's Quartz.IJob.Execute(Quartz.IJobExecutionContext) periodically check some flag to see if an interruption has been requested, and if the flag is set, somehow abort the performance of the rest of the job's work. An example of interrupting a job can be found in the source for the class Example7's DumbInterruptableJob It is legal to use some combination of System.Threading.Monitor.Wait(System.Object) and System.Threading.Monitor.Pulse(System.Object) synchronization within System.Threading.Thread.Interrupt and Quartz.IJob.Execute(Quartz.IJobExecutionContext) in order to have the System.Threading.Thread.Interrupt method block until the Quartz.IJob.Execute(Quartz.IJobExecutionContext) signals that it has noticed the set flag. If the Job performs some form of blocking I/O or similar functions, you may want to consider having the Quartz.IJob.Execute(Quartz.IJobExecutionContext) method store a reference to the calling System.Threading.Thread as a member variable. Then the implementation of this interfaces System.Threading.Thread.Interrupt method can call System.Threading.Thread.Interrupt on that Thread. Before attempting this, make sure that you fully understand what System.Threading.Thread.Interrupt does and doesn't do. Also make sure that you clear the Job's member reference to the Thread when the Execute(..) method exits (preferably in a finally block).

該介面定義了 Interrupt 方法，當調用 Scheduler.Shutdown() 方法時，Quartz.IScheduler 將會調用該方法來中斷正在運行的任務。這就意味著，我們需要自己實現中斷方法來停止當前的 Job 。 通常我們可以通過在任務執行時拿到當前工作的線程，併在中斷時調用線程 Abort 方法的方式來終止當前任務。

    public class CommonInterruptableJob : IInterruptableJob
    {
        private Thread _currentThread;

        public void Execute(IJobExecutionContext context)
        {
            _currentThread = Thread.CurrentThread;
            try
            {
                //TODO:編寫你的任務代碼
            }
            finally
            {
                _currentThread = null;
            }
        }

        public void Interrupt()
        {
            if (_currentThread != null)
            {
                _currentThread.Abort();
                _currentThread = null;
            }
        }
    }

這種方法簡單粗暴，在一些要求不太嚴格的情況下表現令人滿意。更為優雅的方式是定義布爾型欄位 _stop 預設為 false ，在 Interrupt 方法被調用時將其設置為 true 。在 Execute 時不斷檢測該欄位的值，併在合適的時機退出處理。

    public class NiceInterruptableJob : IInterruptableJob
    {
        private bool _stop;

        public void Execute(IJobExecutionContext context)
        {
            //假設我的任務是迴圈 1000 次處理某數據
            for (var i = 0; !_stop && i < 1000; i++)
            {
                //TODO:處理代碼
            }
        }

        public void Interrupt()
        {
            _stop = true;
        }
    }

本片文章對 Quartz.NET 進行了一個簡單的介紹，且展示了兩種不同的實現任務終止的方式。方式一簡單粗暴，編寫簡單，適合大多數要求不太嚴格的場合。方式二更加優雅，對退出時機的掌控更加精確，不容易出現危險，但編寫更加複雜。