我开发了一个库，它为工作项实现了生产者/消费者模式。工作被出列，并为每个出列的工作项启动一个单独的任务，其中包含失败和成功的延续。
任务继续在完成（或失败）其工作后重新排队工作项。
整个库共享一个 central CancellationTokenSource，在应用程序关闭时触发。
我现在面临重大的内存泄漏。如果任务是使用取消令牌作为参数创建的，那么这些任务似乎会保留在内存中，直到触发取消源（并在稍后处理）。
这可以在此示例代码 (VB.NET) 中重现。主要任务是包装工作项的任务，而后续任务将处理重新安排。
Dim oCancellationTokenSource As New CancellationTokenSource
Dim oToken As CancellationToken = oCancellationTokenSource.Token
Dim nActiveTasks As Integer = 0
Dim lBaseMemory As Long = GC.GetTotalMemory(True)
For iteration = 0 To 100 ' do this 101 times to see how much the memory increases
Dim lMemory As Long = GC.GetTotalMemory(True)
Console.WriteLine("Memory at iteration start: " & lMemory.ToString("N0"))
Console.WriteLine(" to baseline: " & (lMemory - lBaseMemory).ToString("N0"))
For i As Integer = 0 To 1000 ' 1001 iterations to get an immediate, measurable impact
Interlocked.Increment(nActiveTasks)
Dim outer As Integer = i
Dim oMainTask As New Task(Sub()
' perform some work
Interlocked.Decrement(nActiveTasks)
End Sub, oToken)
Dim inner As Integer = 1
Dim oFaulted As Task = oMainTask.ContinueWith(Sub()
Console.WriteLine("Failed " & outer & "." & inner)
' if failed, do something with the work and re-queue it, if possible
' (imagine code for re-queueing - essentially just a synchronized list.add)
' Does not help:
' oMainTask.Dispose()
End Sub, oToken, TaskContinuationOptions.OnlyOnFaulted, TaskScheduler.Default)
' if not using token, does not cause increase in memory:
'End Sub, TaskContinuationOptions.OnlyOnFaulted)
' Does not help:
' oFaulted.ContinueWith(Sub()
' oFaulted.Dispose()
' End Sub, TaskContinuationOptions.NotOnFaulted)
Dim oSucceeded As Task = oMainTask.ContinueWith(Sub()
' success
' re-queue for next iteration
' (imagine code for re-queueing - essentially just a synchronized list.add)
' Does not help:
' oMainTask.Dispose()
End Sub, oToken, TaskContinuationOptions.OnlyOnRanToCompletion, TaskScheduler.Default)
' if not using token, does not cause increase in memory:
'End Sub, TaskContinuationOptions.OnlyOnRanToCompletion)
' Does not help:
' oSucceeded.ContinueWith(Sub()
' oSucceeded.Dispose()
' End Sub, TaskContinuationOptions.NotOnFaulted)
' This does not help either and makes processing much slower due to the thrown exception (at least one of these tasks is cancelled)
'Dim oDisposeTask As New Task(Sub()
' Try
' Task.WaitAll({oMainTask, oFaulted, oSucceeded, oFaultedFaulted, oSuccededFaulted})
' Catch ex As Exception
' End Try
' oMainTask.Dispose()
' oFaulted.Dispose()
' oSucceeded.Dispose()
' End Sub)
oMainTask.Start()
' oDisposeTask.Start()
Next
Console.WriteLine("Memory after creating tasks: " & GC.GetTotalMemory(True).ToString("N0"))
' Wait until all main tasks are finished (may not mean that continuations finished)
Dim previousActive As Integer = nActiveTasks
While nActiveTasks > 0
If previousActive <> nActiveTasks Then
Console.WriteLine("Active: " & nActiveTasks)
Thread.Sleep(500)
previousActive = nActiveTasks
End If
End While
Console.WriteLine("Memory after tasks finished: " & GC.GetTotalMemory(True).ToString("N0"))
Next
我使用 ANTS Memory Profiler 测量了内存使用情况，发现 System.Threading.ExecutionContext 大幅增加，这可以追溯到任务延续和CancellationCallbackInfo.
如您所见，我已经尝试处理使用取消令牌的任务，但这似乎没有效果。
编辑
我正在使用 .NET 4.0
更新
即使只是将主要任务与失败的延续联系起来，内存使用量也会不断增加。任务继续似乎阻止了取消令牌注册的注销。
因此，如果一个任务与一个没有运行的延续链接在一起（由于TaskContinuationOptions），那么似乎存在内存泄漏。如果只有一个继续运行，那么我没有观察到内存泄漏。
解决方法
作为一种解决方法，我可以在没有任何内容的情况下进行单个延续，TaskContinuationOptions并在那里处理父任务的状态：
oMainTask.ContinueWith(Sub(t)
If t.IsCanceled Then
' ignore
ElseIf t.IsCompleted Then
' reschedule
ElseIf t.IsFaulted Then
' error handling
End If
End Sub)
如果取消，我将不得不检查它的执行情况，但这似乎可以解决问题。我几乎怀疑 .NET Framework 中存在错误。具有互斥条件的任务取消并不罕见。