Code
2023-05-27 08:00:01

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

在线程池上运行任务要简单得多，而不是试图欺骗调度器以同步方式运行它。这样可以确保它不会死锁。由于上下文切换会影响性能。

Task<MyResult> DoSomethingAsync() { ... }

// Starts the asynchronous task on a thread-pool thread.
// Returns a proxy to the original task.
Task<MyResult> task = Task.Run(() => DoSomethingAsync());

// Will block until the task is completed...
MyResult result = task.Result;
2013-06-13 18:50:54

其他回答

或者你可以直接说:

customerList = Task.Run<List<Customer>>(() => { return GetCustomers(); }).Result;

要进行编译，请确保引用扩展程序集:

System.Net.Http.Formatting
2016-03-08 23:21:17

使用下面的代码剪辑

Task.WaitAll(Task.Run(async () => await service.myAsyncMethod()));
2016-10-19 04:13:30

这对我很有用

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp2
{
    public static class AsyncHelper
    {
        private static readonly TaskFactory _myTaskFactory = new TaskFactory(CancellationToken.None, TaskCreationOptions.None, TaskContinuationOptions.None, TaskScheduler.Default);

        public static void RunSync(Func<Task> func)
        {
            _myTaskFactory.StartNew(func).Unwrap().GetAwaiter().GetResult();
        }

        public static TResult RunSync<TResult>(Func<Task<TResult>> func)
        {
            return _myTaskFactory.StartNew(func).Unwrap().GetAwaiter().GetResult();
        }
    }

    class SomeClass
    {
        public async Task<object> LoginAsync(object loginInfo)
        {
            return await Task.FromResult(0);
        }
        public object Login(object loginInfo)
        {
            return AsyncHelper.RunSync(() => LoginAsync(loginInfo));
            //return this.LoginAsync(loginInfo).Result.Content;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            var someClass = new SomeClass();

            Console.WriteLine(someClass.Login(1));
            Console.ReadLine();
        }
    }
}
2018-07-27 15:20:06 
    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

如果我没看错你的问题——想要同步调用异步方法的代码正在挂起的调度程序线程上执行。你想要同步地阻塞那个线程直到async方法完成。

c# 5中的异步方法是通过有效地将方法切碎，并返回一个可以跟踪整个shabang的整体完成的Task来实现的。然而，被分割的方法如何执行取决于传递给await操作符的表达式类型。

大多数情况下，您将在Task类型的表达式上使用await。Task对await模式的实现是“智能的”，因为它遵循SynchronizationContext，这基本上会导致以下情况发生:

如果进入await的线程位于Dispatcher或WinForms消息循环线程上，它将确保async方法的块作为消息队列处理的一部分发生。 如果进入await的线程位于线程池线程上，则异步方法的剩余块发生在线程池的任何位置。

这就是为什么您可能会遇到问题——异步方法实现试图在Dispatcher上运行其余部分——即使它被挂起。

．．．． 备份!．...

我要问一个问题，为什么你要在异步方法上同步阻塞?这样做会违背为什么要异步调用该方法的目的。通常，当您开始在Dispatcher或UI方法上使用await时，您将希望将整个UI流转为异步。例如，如果你的调用堆栈如下所示:

(高级)WebRequest.GetResponse () YourCode.HelperMethod () YourCode.AnotherMethod () YourCode.EventHandlerMethod () [UI Code].Plumbing() - WPF或WinForms代码 [消息循环]- WPF或WinForms消息循环

然后，一旦代码转换为使用异步，您通常会得到

(高级)WebRequest.GetResponseAsync () YourCode.HelperMethodAsync () YourCode.AnotherMethodAsync () YourCode.EventHandlerMethodAsync () [UI Code].Plumbing() - WPF或WinForms代码 [消息循环]- WPF或WinForms消息循环

实际回答

上面的AsyncHelpers类实际上可以工作，因为它的行为就像一个嵌套的消息循环，但它将自己的并行机制安装到Dispatcher上，而不是试图在Dispatcher本身上执行。这是解决你的问题的一个办法。

另一种解决方法是在线程池线程上执行async方法，然后等待它完成。这样做很容易-你可以用下面的代码片段来做:

var customerList = TaskEx.RunEx(GetCustomers).Result;

最终的API将是Task.Run(…)，但对于CTP，您将需要Ex后缀(此处解释)。

2011-02-24 21:29:15

推荐文章

aliyun

最新文章

标签

2025 code 京ICP备15047053号-1