我将如何运行异步任务<T>方法同步? [英] How would I run an async Task<T> method synchronously?
问题描述
我正在学习 async/await,遇到了需要同步调用异步方法的情况.我该怎么做?
I am learning about async/await, and ran into a situation where I need to call an async method synchronously. How can I do that?
异步方法:
public async Task<Customers> GetCustomers()
{
return await Service.GetCustomersAsync();
}
正常使用:
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)
我还尝试了来自 的建议这里,但是当调度器处于挂起状态时它不起作用.
I also tried a suggestion from here, however it doesn't work when the dispatcher is in a suspended state.
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();
}
这是调用 RunSynchronously
的异常和堆栈跟踪:
Here is the exception and stack trace from calling RunSynchronously
:
System.InvalidOperationException
System.InvalidOperationException
消息:无法在未绑定到委托的任务上调用 RunSynchronously.
Message: RunSynchronously may not be called on a task unbound to a delegate.
内部异常:空
来源:mscorlib
堆栈跟踪:
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()
推荐答案
这是我发现适用于所有情况(包括暂停的调度程序)的解决方法.这不是我的代码,我仍在努力完全理解它,但它确实有效.
Here's a workaround I found that works for all cases (including suspended dispatchers). It's not my code and I'm still working to fully understand it, but it does work.
可以使用:
customerList = AsyncHelpers.RunSync
>(() => GetCustomers());
代码来自这里一个>
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;
}
}
}
这篇关于我将如何运行异步任务<T>方法同步?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!