IO读写操作的TPL Dataflow实现中的内存问题

Question

我试图使用文件IO操作实现读写操作,并将这些操作封装在一起TransformBlock,以使这些操作线程安全,而不是使用锁定机制.

但问题是,当我尝试并行写入5个文件时,有一个异常的内存,并且在使用此实现时它阻止了UI线程.该实现在Windows Phone项目中完成.请说明这个实现有什么问题.

文件IO操作

public static readonly IsolatedStorageFile _isolatedStore = IsolatedStorageFile.GetUserStoreForApplication();
public static readonly FileIO _file = new FileIO();
public static readonly ConcurrentExclusiveSchedulerPair taskSchedulerPair = new ConcurrentExclusiveSchedulerPair();
public static readonly ExecutionDataflowBlockOptions exclusiveExecutionDataFlow 
    = new ExecutionDataflowBlockOptions
{
    TaskScheduler = taskSchedulerPair.ExclusiveScheduler,
    BoundedCapacity = 1
};

public static readonly ExecutionDataflowBlockOptions concurrentExecutionDataFlow 
    = new ExecutionDataflowBlockOptions
{
    TaskScheduler = taskSchedulerPair.ConcurrentScheduler,
    BoundedCapacity = 1
};

public static async Task<T> LoadAsync<T>(string fileName)
{
    T result = default(T);

    var transBlock = new TransformBlock<string, T>
       (async fName =>
       {
           return await LoadData<T>(fName);
       }, concurrentExecutionDataFlow);

    transBlock.Post(fileName);

    result = await transBlock.ReceiveAsync();

    return result;
}

public static async Task SaveAsync<T>(T obj, string fileName)
{
    var transBlock = new TransformBlock<Tuple<T, string>, Task>
       (async tupleData =>
       {
          await SaveData(tupleData.Item1, tupleData.Item2);
       }, exclusiveExecutionDataFlow);

    transBlock.Post(new Tuple<T, string>(obj, fileName));

    await transBlock.ReceiveAsync();
}

MainPage.xaml.cs用法

private static string data = "vjdsskjfhkjsdhvnvndjfhjvkhdfjkgd"
private static string fileName = string.Empty;
private List<string> DataLstSample = new List<string>();
private ObservableCollection<string> TestResults = new ObservableCollection<string>();
private static string data1 = "hjhkjhkhkjhjkhkhkjhkjhkhjkhjkh";
List<Task> allTsk = new List<Task>();
private Random rand = new Random();
private string  fileNameRand
{
    get
    {
        return rand.Next(100).ToString();
    }
}

public MainPage()
{
    InitializeComponent();

    for (int i = 0; i < 5; i ++)
    {
        DataLstSample.Add((i % 2) == 0 ? data : data1);
    }

}

private void Button_Click(object sender, RoutedEventArgs e)
{
    AppIsolatedStore_TestInMultiThread_LstResultShouldBeEqual();
}

public async void AppIsolatedStore_TestInMultiThread_LstResultShouldBeEqual()
{
    TstRst.Text = "InProgress..";
    allTsk.Clear();

    foreach(var data in DataLstSample)
    {
        var fName = fileNameRand;

        var t = Task.Run(async () =>
        {
            await AppIsolatedStore.SaveAsync<string>(data, fName);
        });

        TestResults.Add(string.Format("Writing file name: {0}, data: {1}", fName, data));
        allTsk.Add(t);
    }

    await Task.WhenAll(allTsk);

    TstRst.Text = "Completed..";
}

保存并加载数据异步

        /// <summary>
        /// Load object from file
        /// </summary>
        private static async Task<T> LoadData<T>(string fileName)
        {

            T result = default(T);

            try
            {
                if (!string.IsNullOrWhiteSpace(fileName))
                {
                    using (var file = new IsolatedStorageFileStream(fileName, FileMode.OpenOrCreate, _isolatedStore))
                    {
                        var data = await _file.ReadTextAsync(file);

                        if (!string.IsNullOrWhiteSpace(data))
                        {
                            result = JsonConvert.DeserializeObject<T>(data);
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                //todo: log the megatron exception in a file
                Debug.WriteLine("AppIsolatedStore: LoadAsync : An error occured while loading data : {0}", ex.Message);
            }
            finally
            {

            }

            return result;
        }


        /// <summary>
        /// Save object from file
        /// </summary>
        private static async Task SaveData<T>(T obj, string fileName)
        {
            try
            {
                if (obj != null && !string.IsNullOrWhiteSpace(fileName))
                {
                    //Serialize object with JSON or XML serializer
                    string storageString = JsonConvert.SerializeObject(obj);

                    if (!string.IsNullOrWhiteSpace(storageString))
                    {
                        //Write content to file
                        await _file.WriteTextAsync(new IsolatedStorageFileStream(fileName, FileMode.Create, _isolatedStore), storageString);
                    }
                }
            }
            catch (Exception ex)
            {
                //todo: log the megatron exception in a file
                Debug.WriteLine("AppIsolatedStore: SaveAsync : An error occured while saving the data : {0}", ex.Message);
            }
            finally
            {
            }
        }

编辑:

它有内存异常的原因是因为我所采用的数据字符串太大的一个原因.字符串是链接:http://1drv.ms/1QWSAsc

但第二个问题是,如果我也添加小数据,那么它阻止了UI线程.代码在UI上执行任何任务吗？

Answer 1

不，您使用并发对，该对使用默认线程池来执行其任务，并使用Run方法实例化任务，因此问题不在这里。但这里的代码有两个主要威胁：

var transBlock = new TransformBlock<string, T>
   (async fName =>
   {
       // process file here
   }, concurrentExecutionDataFlow);

你真的不应该transBlock每次都创建。其主要思想TPL Dataflow是您创建一次块并在之后使用它们。因此，您应该重构您的应用程序以减少实例化的块数量，否则不TPL Dataflow应该使用这种情况。

代码中的另一个威胁是您明确阻止了线程！

// Right here
await Task.WhenAll(allTsk);
TstRst.Text = "Completed..";

从同步事件处理程序的方法调用awaitfor 任务async void会阻塞线程，因为默认情况下它会捕获同步上下文。首先，async void应该避免。其次，如果你是异步的，你应该一直异步，所以事件处理程序也应该是异步的。第三，您可以使用任务的延续来更新 UI 或使用当前同步上下文。

所以，你的代码应该是这样的：

// store the sync context in the field of your form
SynchronizationContext syncContext = SynchronizationContext.Current;

// avoid the async void :)
public async Task AppIsolatedStore_TestInMultiThread_LstResultShouldBeEqual()

// make event handler async - this is the only exception for the async void use rule from above
private async void Button_Click(object sender, RoutedEventArgs e)

// asynchronically wait the result without capturing the context
await Task.WhenAll(allTsk).ContinueWith(
  t => {
    // you can move out this logic to main method
    syncContext.Post(new SendOrPostCallback(o =>
        {
            TstRst.Text = "Completed..";
        }));
  }
);