我如何运行异步任务<T>方法同步?

我正在学习异步/等待，遇到了需要同步调用异步方法的情况。我该怎么做呢?

异步方法:

public async Task<Customers> GetCustomers()
{
    return await Service.GetCustomersAsync();
}

正常的用法:

public async void GetCustomers()
{
    customerList = await GetCustomers();
}

我尝试使用以下方法:

Task<Customer> task = GetCustomers();
task.Wait()

Task<Customer> task = GetCustomers();
task.RunSynchronously();

Task<Customer> task = GetCustomers();
while(task.Status != TaskStatus.RanToCompletion)

我还尝试了这里的一个建议，但是当调度程序处于挂起状态时，它不起作用。

public static void WaitWithPumping(this Task task) 
{
        if (task == null) throw new ArgumentNullException(“task”);
        var nestedFrame = new DispatcherFrame();
        task.ContinueWith(_ => nestedFrame.Continue = false);
        Dispatcher.PushFrame(nestedFrame);
        task.Wait();
}

下面是调用runsynchronically时的异常和堆栈跟踪:

系统。InvalidOperationException 消息:在未绑定到委托的任务上不能调用runsynchronically。 InnerException:零来源:mscorlib 加:

          at System.Threading.Tasks.Task.InternalRunSynchronously(TaskScheduler scheduler)
   at System.Threading.Tasks.Task.RunSynchronously()
   at MyApplication.CustomControls.Controls.MyCustomControl.CreateAvailablePanelList() in C:\Documents and Settings\...\MyApplication.CustomControls\Controls\MyCustomControl.xaml.cs:line 638
   at MyApplication.CustomControls.Controls.MyCustomControl.get_AvailablePanels() in C:\Documents and Settings\...\MyApplication.CustomControls\Controls\MyCustomControl.xaml.cs:line 233
   at MyApplication.CustomControls.Controls.MyCustomControl.<CreateOpenPanelList>b__36(DesktopPanel panel) in C:\Documents and Settings\...\MyApplication.CustomControls\Controls\MyCustomControl.xaml.cs:line 597
   at System.Collections.Generic.List`1.ForEach(Action`1 action)
   at MyApplication.CustomControls.Controls.MyCustomControl.<CreateOpenPanelList>d__3b.MoveNext() in C:\Documents and Settings\...\MyApplication.CustomControls\Controls\MyCustomControl.xaml.cs:line 625
   at System.Runtime.CompilerServices.TaskAwaiter.<>c__DisplayClass7.<TrySetContinuationForAwait>b__1(Object state)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
   at System.Threading.ExecutionContext.runTryCode(Object userData)
   at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.Run()
   at System.Windows.Application.RunDispatcher(Object ignore)
   at System.Windows.Application.RunInternal(Window window)
   at System.Windows.Application.Run(Window window)
   at System.Windows.Application.Run()
   at MyApplication.App.Main() in C:\Documents and Settings\...\MyApplication\obj\Debug\App.g.cs:line 50
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
   at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.ThreadHelper.ThreadStart()

当前回答

这对我来说很有效

public static class TaskHelper
{
    public static void RunTaskSynchronously(this Task t)
    {
        var task = Task.Run(async () => await t);
        task.Wait();
    }

    public static T RunTaskSynchronously<T>(this Task<T> t)
    {
        T res = default(T);
        var task = Task.Run(async () => res = await t);
        task.Wait();
        return res;
    }
}

2014-07-23 05:42:37

其他回答

尝试以下代码，它为我工作:

public async void TaskSearchOnTaskList (SearchModel searchModel)
{
    try
    {
        List<EventsTasksModel> taskSearchList = await Task.Run(
            () => MakeasyncSearchRequest(searchModel),
            cancelTaskSearchToken.Token);

        if (cancelTaskSearchToken.IsCancellationRequested
                || string.IsNullOrEmpty(rid_agendaview_search_eventsbox.Text))
        {
            return;
        }

        if (taskSearchList == null || taskSearchList[0].result == Constants.ZERO)
        {
            RunOnUiThread(() => {
                textViewNoMembers.Visibility = ViewStates.Visible;                  
                taskListView.Visibility = ViewStates.Gone;
            });

            taskSearchRecureList = null;

            return;
        }
        else
        {
            taskSearchRecureList = TaskFooterServiceLayer
                                       .GetRecurringEvent(taskSearchList);

            this.SetOnAdapter(taskSearchRecureList);
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine("ActivityTaskFooter -> TaskSearchOnTaskList:" + ex.Message);
    }
}

2015-09-03 07:39:35

为什么不创建一个这样的呼叫:

Service.GetCustomers();

这不是异步的。

2011-02-23 18:20:34

注意:我认为作为最佳实践，不建议改变操作的性质，如果它是异步的，最好的事情是处理它(异步的所有方式)。通过这种方式，您可以获得其他好处，如并行处理/多线程等。

看到其他答案没有使用这种方法，我也想把它贴在这里:

var customers = GetCustomersAsync().GetAwaiter().GetResult();

2020-11-16 20:34:20

    private int GetSync()
    {
        try
        {
            ManualResetEvent mre = new ManualResetEvent(false);
            int result = null;

            Parallel.Invoke(async () =>
            {
                result = await SomeCalcAsync(5+5);
                mre.Set();
            });

            mre.WaitOne();
            return result;
        }
        catch (Exception)
        {
            return null;
        }
    }

2013-09-27 20:29:16

在代码中，第一个等待任务执行，但是你还没有启动它，所以它会无限期地等待。试试这个:

Task<Customer> task = GetCustomers();
task.RunSynchronously();

编辑:

你说你得到了一个异常。请发布更多细节，包括堆栈跟踪。 Mono包含以下测试用例:

[Test]
public void ExecuteSynchronouslyTest ()
{
        var val = 0;
        Task t = new Task (() => { Thread.Sleep (100); val = 1; });
        t.RunSynchronously ();

        Assert.AreEqual (1, val);
}

检查一下这对你是否有效。如果没有，尽管不太可能，你可能会有一些奇怪的Async CTP构建。如果它可以工作，您可能需要检查编译器到底生成了什么，以及Task实例化与这个示例有什么不同。

编辑# 2:

我检查了反射器，你所描述的异常发生时m_action为空。这有点奇怪，但我不是异步CTP的专家。正如我所说，你应该反编译你的代码，看看Task是如何被实例化的，不管它的m_action是如何为空的。

2011-02-23 18:23:15

我如何运行异步任务<T>方法同步?

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