我在VS2013,.NET FW 4.5.1中开发WinForms应用程序。这是我的简化代码,其中包含有关结构的内联注释:
// Progress object implementing IProgress<MyProgressData>
var progressCallback = new Progress<MyProgressData>();
// listOfMyList is actually List<List<MyObject>>, which contains list of
// list of MyObject's which will be executed as tasks at once.
// For example, this would be sample structure for list of lists:
// List1
// MyObject1
// MyObject2
// MyObject3
// List2
// MyObject4
// MyObject5
// MyObject6
// List1's and List2's objects would be executed as all tasks at once, but List1 and List2 respectively
// would be executed one after another (because of resources usage inside TASK CODE)
foreach (var myItem in listOfMyList)
{
var myList = myItem.ToList();
// Create a list of tasks to be executed (20 by default; each taking from 30-60 seconds)
// Here cs is actually MyObject
var myTasks = myList.Select(cs => Task.Run(async () =>
{
// TASK CODE (using cs as an input object and using "cancellationToken.ThrowIfCancellationRequested();" inside execution to cancel executing if requested)
}, cancellationToken));
await Task.WhenAll(myTasks); // Wait for all tasks to finish
// Report progress to main form (this actually calls an event on my form)
await Task.Run(() => progressCallback.Report(new MyProgressData() { props }), CancellationToken.None);
}
如您所见,我构建进度对象,然后我有列表列表。顶级列表中的每个项目应以序列化方式(一个接一个)执行。每个项目的列表元素应该以任务的形式一次执行。 到目前为止一切顺利,所有任务都开始了,甚至在等待它们的时候。或者至少我是这么认为的。我已将日志记录放入相关方法中,以显示代码执行情况。事实证明,当执行逻辑(在底部)正在执行时,foreach循环开始执行另一批任务,它不应该。 我在这里错过了什么吗?进度代码是否阻止或等待Report方法完成执行。也许我错过了关于异步/等待的事情。等待我们确保代码不会继续,直到方法完成后?它不会阻止当前线程,但它也不会继续执行? 甚至可能(因为它发生了,它可能是),因为我的foreach循环继续执行而进度报告仍然在进行中?
此代码驻留在异步方法中。它实际上是这样调用的(假设这个方法是async MyProblematicMethod()
):
while (true)
{
var result = await MyProblematicMethod();
if (result.HasToExitWhile)
break;
}
MyProblematicMethod中的每个方法都使用await来等待异步方法,并且不会多次调用。
答案 0 :(得分:0)
根据Glorin的建议,IProgress.Report在触发事件处理程序后立即返回,我已经创建了Progress类的精确副本,它使用了SyncContext.Send而不是Post:
public sealed class ProgressEx<T> : IProgress<T>
{
private readonly SynchronizationContext _synchronizationContext;
private readonly Action<T> _handler;
private readonly SendOrPostCallback _invokeHandlers;
public event EventHandler<T> ProgressChanged;
public ProgressEx(SynchronizationContext syncContext)
{
// From Progress.cs
//_synchronizationContext = SynchronizationContext.CurrentNoFlow ?? ProgressStatics.DefaultContext;
_synchronizationContext = syncContext;
_invokeHandlers = new SendOrPostCallback(InvokeHandlers);
}
public ProgressEx(SynchronizationContext syncContext, Action<T> handler)
: this(syncContext)
{
if (handler == null)
throw new ArgumentNullException("handler");
_handler = handler;
}
private void OnReport(T value)
{
// ISSUE: reference to a compiler-generated field
if (_handler == null && ProgressChanged == null)
return;
_synchronizationContext.Send(_invokeHandlers, (object)value);
}
void IProgress<T>.Report(T value)
{
OnReport(value);
}
private void InvokeHandlers(object state)
{
T e = (T)state;
Action<T> action = _handler;
// ISSUE: reference to a compiler-generated field
EventHandler<T> eventHandler = ProgressChanged;
if (action != null)
action(e);
if (eventHandler == null)
return;
eventHandler((object)this, e);
}
}
这意味着ProgressEx.Report将在返回之前等待方法完成。也许不是所有情况下的最佳解决方案,但在这种情况下它对我有用。
要调用它,只需使用SynchronizationContext.Current
创建ProgressEx作为构造函数的参数。但是,它必须在UI线程中创建,因此传入正确的SynchronizationContext。例如。 new ProgressEx<MyDataObject>(SynchronizationContext.Current)