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

在。net 4.6中测试。它还可以避免死锁。

对于返回Task的异步方法。

Task DoSomeWork();
Task.Run(async () => await DoSomeWork()).Wait();

对于返回Task<T>的异步方法

Task<T> GetSomeValue();
var result = Task.Run(() => GetSomeValue()).Result;

编辑:

如果调用者在线程池线程中运行(或者调用者也在任务中)，在某些情况下仍然可能导致死锁。

2018-10-24 09:08:51

其他回答

注意一下，这种方法:

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

为WinRT工作。

让我解释一下:

private void TestMethod()
{
    Task<Customer> task = GetCustomers(); // call async method as sync and get task as result
    task.Wait(); // wait executing the method
    var customer = task.Result; // get's result.
    Debug.WriteLine(customer.Name); //print customer name
}
public class Customer
{
    public Customer()
    {
        new ManualResetEvent(false).WaitOne(TimeSpan.FromSeconds(5));//wait 5 second (long term operation)
    }
    public string Name { get; set; }
}
private Task<Customer> GetCustomers()
{
    return Task.Run(() => new Customer
    {
        Name = "MyName"
    });
}

此外，这种方法只适用于Windows商店解决方案!

注意:如果你在其他异步方法中调用你的方法，这种方法是不线程安全的(根据@Servy的评论)

2012-06-20 22:10:20

我遇到过几次，主要是在单元测试或windows服务开发中。目前我一直在使用这个功能:

        var runSync = Task.Factory.StartNew(new Func<Task>(async () =>
        {
            Trace.WriteLine("Task runSync Start");
            await TaskEx.Delay(2000); // Simulates a method that returns a task and
                                      // inside it is possible that there
                                      // async keywords or anothers tasks
            Trace.WriteLine("Task runSync Completed");
        })).Unwrap();
        Trace.WriteLine("Before runSync Wait");
        runSync.Wait();
        Trace.WriteLine("After runSync Waited");

这很简单，很容易，我没有任何问题。

2013-10-05 02:54:50

我发现SpinWait在这方面工作得很好。

var task = Task.Run(()=>DoSomethingAsyncronous());

if(!SpinWait.SpinUntil(()=>task.IsComplete, TimeSpan.FromSeconds(30)))
{//Task didn't complete within 30 seconds, fail...
   return false;
}

return true;

上述方法不需要使用. result或. wait()。它还允许您指定一个超时，以便在任务从未完成的情况下，您不会永远卡住。

2019-02-06 22:02:41

在。net 4.6中测试。它还可以避免死锁。

对于返回Task的异步方法。

Task DoSomeWork();
Task.Run(async () => await DoSomeWork()).Wait();

对于返回Task<T>的异步方法

Task<T> GetSomeValue();
var result = Task.Run(() => GetSomeValue()).Result;

编辑:

如果调用者在线程池线程中运行(或者调用者也在任务中)，在某些情况下仍然可能导致死锁。

2018-10-24 09:08:51

请注意，这个答案是三年前的。我主要是根据。net 4.0的使用经验编写的，很少使用4.5，尤其是async-await。一般来说，这是一个很好的简单的解决方案，但有时它会破坏一些东西。请阅读评论中的讨论。

net 4.5

就用这个吧:

// For Task<T>: will block until the task is completed...
var result = task.Result; 

// For Task (not Task<T>): will block until the task is completed...
task2.RunSynchronously();

看到的: TaskAwaiter, 的任务。结果, 的任务。RunSynchronously

net 4.0

用这个:

var x = (IAsyncResult)task;
task.Start();

x.AsyncWaitHandle.WaitOne();

.．.或:

task.Start();
task.Wait();

2012-08-02 17:03:47

我如何运行异步任务<T>方法同步?

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