multithreading - WP7-在停用或关闭应用程序时无法正常退出bg线程时遇到麻烦

Question

我的数据密集型wp7应用程序按以下方式持久存储数据:我维护一个反射(reflect)所有用户 Activity 的变更日志，每隔几秒钟，线程计时器就会启动一个线程池线程，该线程将变更日志刷新到事务内的数据库中。看起来像这样:

当用户退出时，我停止计时器，刷新UI线程上的日志(不超过一两秒钟)，然后卸下数据库。

但是，如果在用户退出时工作线程处于 Activity 状态，则无法弄清楚如何正常响应。系统似乎杀死了工作线程，因此它永远不会完成工作，也永远不会放弃对数据库连接的锁定，然后ui线程会尝试获取该锁定，并立即被系统杀死。我尝试在UI线程上设置一个标志以请求工作程序中止，但是我认为工作程序在读取该标志之前已被中断。一切正常，除了这种情况，即每100个场景中有1个场景，其中某些用户更改最终没有保存到数据库，而我似乎无法解决这一问题。

下面的代码非常简化:

private Timer _SweepTimer = new Timer(SweepCallback, null, 5000, 5000);

private volatile bool _BailOut = false;
private void SweepCallback(object state) {
    lock (db) { 
        db.startTransaction();

        foreach(var entry in changeJournal){
            //CRUD entry as appropriate
            if(_BailOut){
                db.rollbackTransaction();
                return;
            }
        }

        db.endTransaction();
        changeJournal.Clear();
    }
}

private void RespondToSystemExit(){
    _BailOut = true; //Set flag for worker to exit

    lock(db){ //In theory, should acquire the lock after the bg thread bails out
        SweepCallback(null);//Flush to db on the UI thread
        db.dismount();//App is now ready to close
    }
}

Answer 1

好了，只是为了解决这个问题，我最终使用了一个manualresetevent而不是锁定，据我所知，这是对manualresetevent的误用，既冒险又骇人，但总比没有好。

我仍然不知道为什么我的原始代码无法正常工作。

编辑:为了后代，我在重新发布代码以从MS论坛中重现此代码:

//This is a functioning console app showing the code working as it should. Press "w" and then "i" to start and then interrupt the worker
using System;
using System.Threading;

namespace deadlocktest {
    class Program {
        static void Main(string[] args) {
            var tester = new ThreadTest();
            string input = "";
            while (!input.Equals("x")) {
                input = Console.ReadLine();

                switch (input) {
                    case "w":
                        tester.StartWorker();
                        break;
                    case "i":
                        tester.Interrupt();
                        break;
                    default:
                        return;
                }
            }
        }
    }

    class ThreadTest{
        private Object lockObj = new Object();
        private volatile bool WorkerCancel = false;

        public void StartWorker(){
            ThreadPool.QueueUserWorkItem((obj) => {
                if (Monitor.TryEnter(lockObj)) {
                    try {
                        Log("Worker acquired the lock");
                        for (int x = 0; x < 10; x++) {
                            Thread.Sleep(1200);
                            Log("Worker: tick" + x.ToString());
                            if (WorkerCancel) {
                                Log("Worker received exit signal, exiting");
                                WorkerCancel = false;
                                break;
                            }
                        }
                    } finally {
                        Monitor.Exit(lockObj);
                        Log("Worker released the lock");
                    }
                } else {
                    Log("Worker failed to acquire lock");
                }
            });
        }

        public void Interrupt() {
            Log("UI thread - Setting interrupt flag");
            WorkerCancel = true;

            if (Monitor.TryEnter(lockObj, 5000)) {
                try {
                    Log("UI thread - successfully acquired lock from worker");
                } finally {
                    Monitor.Exit(lockObj);
                    Log("UI thread - Released the lock");
                }
            } else {
                Log("UI thread - failed to acquire the lock from the worker");
            }
        }

        private void Log(string Data) {
            Console.WriteLine(string.Format("{0} - {1}", DateTime.Now.ToString("mm:ss:ffff"), Data));
        }
    }
}

这是几乎相同的代码，它们对于WP7都失败了，只需要创建一个带有两个按钮的页面并将其钩住即可

using System;
using System.Diagnostics;
using System.Threading;
using System.Windows;
using Microsoft.Phone.Controls;

namespace WorkerThreadDemo {
    public partial class MainPage : PhoneApplicationPage {
        public MainPage() {
            InitializeComponent();
        }

        private Object lockObj = new Object();
        private volatile bool WorkerCancel = false;
        private void buttonStartWorker_Click(object sender, RoutedEventArgs e) {
            ThreadPool.QueueUserWorkItem((obj) => {
                if (Monitor.TryEnter(lockObj)) {
                    try {
                        Log("Worker acquired the lock");
                        for (int x = 0; x < 10; x++) {
                            Thread.Sleep(1200);
                            Log("Worker: tick" + x.ToString());
                            if (WorkerCancel) {
                                Log("Worker received exit signal, exiting");
                                WorkerCancel = false;
                                break;
                            }
                        }
                    } finally {
                        Monitor.Exit(lockObj);
                        Log("Worker released the lock");
                    }
                } else {
                    Log("Worker failed to acquire lock");
                }
            });
        }

        private void Log(string Data) {
            Debug.WriteLine(string.Format("{0} - {1}", DateTime.Now.ToString("mm:ss:ffff"), Data));
        }

        private void buttonInterrupt_Click(object sender, RoutedEventArgs e) {
            Log("UI thread - Setting interrupt flag");
            WorkerCancel = true;

            //Thread.Sleep(3000); UNCOMMENT ME AND THIS WILL START TO WORK! 
            if (Monitor.TryEnter(lockObj, 5000)) {
                try {
                    Log("UI thread - successfully acquired lock from worker");
                } finally {
                    Monitor.Exit(lockObj);
                    Log("UI thread - Released the lock");
                }
            } else {
                Log("UI thread - failed to acquire the lock from the worker");
            }
        }
    }
}