我将如何同步运行异步任务<T>方法？
我正在学习异步/等待，并遇到了需要同步调用异步方法的情况。 我怎样才能做到这一点？
异步方法：
public async Task<Customers> GetCustomers()
{
return await Service.GetCustomersAsync();
}
正常用法：
public async void GetCustomers()
{
customerList = await GetCustomers();
}
我试过使用以下内容：
Task<Customer> task = GetCustomers();
task.Wait()
Task<Customer> task = GetCustomers();
task.RunSynchronously();
Task<Customer> task = GetCustomers();
while(task.Status != TaskStatus.RanToCompletion)
我也从这里尝试了一个建议，但是当调度员处于暂停状态时它不起作用。
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();
}
这是从调用RunSynchronously异常和堆栈跟踪：
System.InvalidOperationException
消息 ：RunSynchronously可能不会在未绑定到委托的任务上调用。
InnerException ：null
来源 ：mscorlib
StackTrace ：
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.CustomControlsControlsMyCustomControl.xaml.cs:line 638
at MyApplication.CustomControls.Controls.MyCustomControl.get_AvailablePanels() in C:Documents and Settings...MyApplication.CustomControlsControlsMyCustomControl.xaml.cs:line 233
at MyApplication.CustomControls.Controls.MyCustomControl.<CreateOpenPanelList>b__36(DesktopPanel panel) in C:Documents and Settings...MyApplication.CustomControlsControlsMyCustomControl.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.CustomControlsControlsMyCustomControl.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...MyApplicationobjDebugApp.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()
以下是我发现的解决方法，适用于所有情况（包括暂停调度程序）。 这不是我的代码，我仍然在努力完全理解它，但它确实有效。
它可以使用以下方式调用：
customerList = AsyncHelpers.RunSync<List<Customer>>(() => GetCustomers());
代码来自这里
public static class AsyncHelpers
{
/// <summary>
/// Execute's an async Task<T> method which has a void return value synchronously
/// </summary>
/// <param name="task">Task<T> method to execute</param>
public static void RunSync(Func<Task> task)
{
var oldContext = SynchronizationContext.Current;
var synch = new ExclusiveSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(synch);
synch.Post(async _ =>
{
try
{
await task();
}
catch (Exception e)
{
synch.InnerException = e;
throw;
}
finally
{
synch.EndMessageLoop();
}
}, null);
synch.BeginMessageLoop();
SynchronizationContext.SetSynchronizationContext(oldContext);
}
/// <summary>
/// Execute's an async Task<T> method which has a T return type synchronously
/// </summary>
/// <typeparam name="T">Return Type</typeparam>
/// <param name="task">Task<T> method to execute</param>
/// <returns></returns>
public static T RunSync<T>(Func<Task<T>> task)
{
var oldContext = SynchronizationContext.Current;
var synch = new ExclusiveSynchronizationContext();
SynchronizationContext.SetSynchronizationContext(synch);
T ret = default(T);
synch.Post(async _ =>
{
try
{
ret = await task();
}
catch (Exception e)
{
synch.InnerException = e;
throw;
}
finally
{
synch.EndMessageLoop();
}
}, null);
synch.BeginMessageLoop();
SynchronizationContext.SetSynchronizationContext(oldContext);
return ret;
}
private class ExclusiveSynchronizationContext : SynchronizationContext
{
private bool done;
public Exception InnerException { get; set; }
readonly AutoResetEvent workItemsWaiting = new AutoResetEvent(false);
readonly Queue<Tuple<SendOrPostCallback, object>> items =
new Queue<Tuple<SendOrPostCallback, object>>();
public override void Send(SendOrPostCallback d, object state)
{
throw new NotSupportedException("We cannot send to our same thread");
}
public override void Post(SendOrPostCallback d, object state)
{
lock (items)
{
items.Enqueue(Tuple.Create(d, state));
}
workItemsWaiting.Set();
}
public void EndMessageLoop()
{
Post(_ => done = true, null);
}
public void BeginMessageLoop()
{
while (!done)
{
Tuple<SendOrPostCallback, object> task = null;
lock (items)
{
if (items.Count > 0)
{
task = items.Dequeue();
}
}
if (task != null)
{
task.Item1(task.Item2);
if (InnerException != null) // the method threw an exeption
{
throw new AggregateException("AsyncHelpers.Run method threw an exception.", InnerException);
}
}
else
{
workItemsWaiting.WaitOne();
}
}
}
public override SynchronizationContext CreateCopy()
{
return this;
}
}
}
被告知这个答案是三岁。 我主要基于.Net 4.0的经验编写它，而在4.5版本中很少，尤其是async-await 。 一般来说这是一个很好的简单解决方案，但它有时会破坏一些东西。 请阅读评论中的讨论。
.Net 4.5
只需使用这个：
// 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();
请参阅：TaskAwaiter，Task.Result，Task.RunSynchronously
.Net 4.0
用这个：
var x = (IAsyncResult)task;
task.Start();
x.AsyncWaitHandle.WaitOne();
...或这个：
task.Start();
task.Wait();
惊讶没有人提到这个：
public Task<int> BlahAsync()
{
// ...
}
int result = BlahAsync().GetAwaiter().GetResult();
不像其他一些方法那么漂亮，但它具有以下优点：
Wait ） AggregateException抛出的任何异常（如Result ） Task和Task<T> （自己尝试一下！） 此外，由于GetAwaiter是鸭式输入，因此它适用于从异步方法（如ConfiguredAwaitable或YieldAwaitable ）返回的任何对象，而不仅仅是任务。
编辑：请注意，这种方法（或使用.Result ）可能会死锁，除非每次等待时确保添加.ConfigureAwait(false) ，对于可能从BlahAsync()获得的所有异步方法只是它直接调用的那些）。 说明。
// In BlahAsync() body
await FooAsync(); // BAD!
await FooAsync().ConfigureAwait(false); // Good... but make sure FooAsync() and
// all its descendants use ConfigureAwait(false)
// too. Then you can be sure that
// BlahAsync().GetAwaiter().GetResult()
// won't deadlock.
如果你懒得添加.ConfigureAwait(false)无处不在，而且你不关心性能，你可以选择做
Task.Run(() => BlahAsync()).GetAwaiter().GetResult()