这篇文章起源于昨天的一位朋友发给我的dump文件,说它的程序出现了卡死,看了下程序的主线程栈,居然又碰到了 OnUserPreferenceChanged 导致的挂死问题,真的是经典中的经典,线程栈如下:
0:000:x86> !clrstack
OS Thread Id: 0x4eb688 (0)
Child SP IP Call Site
002fed38 0000002b [HelperMethodFrame_1OBJ: 002fed38] System.Threading.WAItHandle.WaitOneNative(System.Runtime.InteropServices.SafeHandle, UInt32, Boolean, Boolean)
002fee1c 5cddad21 System.Threading.WaitHandle.InternalWaitOne(System.Runtime.InteropServices.SafeHandle, Int64, Boolean, Boolean)
002fee34 5cddace8 System.Threading.WaitHandle.WaitOne(Int32, Boolean)
002fee48 538d876c System.windows.Forms.Control.WaitForWaitHandle(System.Threading.WaitHandle)
002fee88 53c5214a System.Windows.Forms.Control.MarshaledInvoke(System.Windows.Forms.Control, System.Delegate, System.Object[], Boolean)
002fee8c 538dab4b [InlinedCallFrame: 002fee8c]
002fef14 538dab4b System.Windows.Forms.Control.Invoke(System.Delegate, System.Object[])
002fef48 53b03bc6 System.Windows.Forms.WindowsFormsSynchronizationContext.Send(System.Threading.SendOrPostCallback, System.Object)
002fef60 5c774708 Microsoft.Win32.SystemEvents+SystemEventInvokeInfo.Invoke(Boolean, System.Object[])
002fef94 5c6616ec Microsoft.Win32.SystemEvents.RaiseEvent(Boolean, System.Object, System.Object[])
002fefe8 5c660cd4 Microsoft.Win32.SystemEvents.OnUserPreferenceChanged(Int32, IntPtr, IntPtr)
002ff008 5c882c98 Microsoft.Win32.SystemEvents.WindowProc(IntPtr, Int32, IntPtr, IntPtr)
...
说实话,这种dump从去年看到今年,应该不下五次了,都看烦了,其形成原因是:
虽然知道原因,但有一个非常大的遗憾就是在 dump 中找不到到底是哪一个控件,只能笼统地告诉朋友,让其洞察下代码是哪里用了工作线程创建了 用户控件, 有些朋友根据这个信息成功地找到,也有朋友因为各种原因没有找到,比较遗憾。
为了不让这些朋友的遗憾延续下去,这一篇做一个系统归纳,希望能助这些朋友一臂之力。
这个问题的形成详情,我在去年的一篇文章为:记一次 .NET 某新能源汽车锂电池检测程序 UI挂死分析 中已经做过分享,因为 dump 中找不到问题的 Control,所以也留下了一些遗憾,这一篇就做个补充。
熟悉 WinForm 底层的朋友应该知道,一旦在 工作线程 上创建了 Control 控件,框架会自动给这个线程配备一个
WindowsFormsSynchronizationContext 和其底层的 MarshalingControl ,这个是有源码支撑的,大家可以找下 Control 的构造函数,简化后的源码如下:
public class Control : Component
{
internal Control(bool autoInstallSyncContext)
{
//***
if (autoInstallSyncContext)
{
WindowsFormsSynchronizationContext.InstallIfNeeded();
}
}
}
public sealed class WindowsFormsSynchronizationContext : SynchronizationContext, IDisposable
{
private Control controlToSendTo;
private WeakReference destinationThreadRef;
public WindowsFormsSynchronizationContext()
{
DestinationThread = Thread.CurrentThread;
Application.ThreadContext threadContext = Application.ThreadContext.FromCurrent();
if (threadContext != null)
{
controlToSendTo = threadContext.MarshalingControl;
}
}
internal static void InstallIfNeeded()
{
try
{
SynchronizationContext synchronizationContext = AsyncOperationManager.SynchronizationContext;
if (synchronizationContext == null || synchronizationContext.GetType() == typeof(SynchronizationContext))
{
AsyncOperationManager.SynchronizationContext = new WindowsFormsSynchronizationContext();
}
}
finally
{
inSyncContextInstallation = false;
}
}
}
public sealed class WindowsFormsSynchronizationContext : SynchronizationContext, IDisposable
{
public WindowsFormsSynchronizationContext()
{
DestinationThread = Thread.CurrentThread;
Application.ThreadContext threadContext = Application.ThreadContext.FromCurrent();
if (threadContext != null)
{
controlToSendTo = threadContext.MarshalingControl;
}
}
}
internal sealed class ThreadContext
{
internal Control MarshalingControl
{
get
{
lock (this)
{
if (marshalingControl == null)
{
marshalingControl = new MarshalingControl();
}
return marshalingControl;
}
}
}
}
这段代码可以挖到下面两点信息。
0:000:x86> !dso
OS Thread Id: 0x4eb688 (0)
ESP/REG Object Name
002FEC40 025a0fb0 System.Windows.Forms.WindowsFormsSynchronizationContext
...
002FEF44 0260992c System.Object[] (System.Object[])
002FEF48 02d69164 System.Windows.Forms.WindowsFormsSynchronizationContext
...
0:000:x86> !do 02d69164
Name: System.Windows.Forms.WindowsFormsSynchronizationContext
Fields:
MT Field Offset Type VT Attr Value Name
...
533c2204 4002522 8 ...ows.Forms.Control 0 instance 02d69218 controlToSendTo
5cef92d0 4002523 c System.WeakReference 0 instance 02d69178 destinationThreadRef
0:000:x86> !DumpObj /d 02d69178
Name: System.WeakReference
MethodTable: 5cef92d0
EEClass: 5cabf0cc
Size: 12(0xc) bytes
File: C:WindowsMicrosoft.NetassemblyGAC_32mscorlibv4.0_4.0.0.0__b77a5c561934e089mscorlib.dll
Fields:
MT Field Offset Type VT Attr Value Name
5cee2bdc 400070a 4 System.IntPtr 1 instance 111828 m_handle
0:000:x86> !do poi(111828)
Name: System.Threading.Thread
Fields:
MT Field Offset Type VT Attr Value Name
5cee1638 40018ca 28 System.Int32 1 instance 9 m_ManagedThreadId
...
从上面的输出中可以看到,9号线程 曾经创建了不该创建的 Control,所以找出这个 Control 就是解决问题的关键,这也是最难的。
以我目前的技术实力,从 dump 中确实找不到,但我可以运行时监测,突破点就是一旦这个 Control 在工作线程中创建,底层会安排一个
WindowsFormsSynchronizationContext 以及 MarshalingControl 对象,我们拦截他们的生成构造就好了。
为了方便讲述,先上一段测试代码,在 backgroundWorker1_DoWork 方法中创建一个 Button 控件。
namespace WindowsFormsApp1
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
Button btn = new Button();
}
private void Form1_Load(object sender, EventArgs e)
{
}
private void button1_Click(object sender, EventArgs e)
{
backgroundWorker1.RunWorkerAsync();
}
}
}
接下来在 MarshalingControl 的构造函数上下一个bp断点来自动化记录,观察 new Button 的时候是否命中。
0:007> !name2ee System_Windows_Forms_ni System.Windows.Forms.Application+MarshalingControl..ctor
Module: 5b9b1000
Assembly: System.Windows.Forms.dll
Token: 0600554a
MethodDesc: 5b9fe594
Name: System.Windows.Forms.Application+MarshalingControl..ctor()
JITTED Code Address: 5bb5d1a4
0:007> bp 5bb5d1a4 "!clrstack; gc"
0:007> g
OS Thread Id: 0x249c (9)
Child SP IP Call Site
067ff2f0 5bb5d1a4 System.Windows.Forms.Application+MarshalingControl..ctor()
067ff2f4 5bb70224 System.Windows.Forms.Application+ThreadContext.get_MarshalingControl()
067ff324 5bb6fe5d System.Windows.Forms.WindowsFormsSynchronizationContext..ctor()
067ff338 5bb6fd4d System.Windows.Forms.WindowsFormsSynchronizationContext.InstallIfNeeded()
067ff364 5bb6e9a0 System.Windows.Forms.Control..ctor(Boolean)
067ff41c 5bbcd5cc System.Windows.Forms.ButtonBase..ctor()
067ff428 5bbcd531 System.Windows.Forms.Button..ctor()
067ff434 02342500 WindowsFormsApp1.Form1.backgroundWorker1_DoWork(System.Object, System.ComponentModel.DoWorkEventArgs)
067ff488 630ee649 System.ComponentModel.BackgroundWorker.OnDoWork(System.ComponentModel.DoWorkEventArgs) [f:ddNDPfxsrccompmodsystemcomponentmodelBackgroundWorker.cs @ 107]
067ff49c 630ee55d System.ComponentModel.BackgroundWorker.WorkerThreadStart(System.Object) [f:ddNDPfxsrccompmodsystemcomponentmodelBackgroundWorker.cs @ 245]
067ff6a0 7c69f036 [HelperMethodFrame_PROTECTOBJ: 067ff6a0] System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr, System.Object[], System.Object, System.Object[] ByRef)
067ff95c 6197c82c System.Runtime.Remoting.Messaging.StackBuilderSink.AsyncProcessMessage(System.Runtime.Remoting.Messaging.IMessage, System.Runtime.Remoting.Messaging.IMessageSink)
067ff9b0 61978274 System.Runtime.Remoting.Proxies.AgileAsyncWorkerItem.DoAsyncCall() [f:ddndpclrsrcBCLsystemruntimeremotingremotingproxy.cs @ 760]
067ff9bc 61978238 System.Runtime.Remoting.Proxies.AgileAsyncWorkerItem.ThreadPoolCallBack(System.Object) [f:ddndpclrsrcBCLsystemruntimeremotingremotingproxy.cs @ 753]
067ff9c0 6104e7b4 System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(System.Object) [f:ddndpclrsrcBCLsystemthreadingthreadpool.cs @ 1274]
067ff9c8 61078604 System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean) [f:ddndpclrsrcBCLsystemthreadingexecutioncontext.cs @ 980]
067ffa34 61078537 System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean) [f:ddndpclrsrcBCLsystemthreadingexecutioncontext.cs @ 928]
067ffa48 6104f445 System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem() [f:ddndpclrsrcBCLsystemthreadingthreadpool.cs @ 1252]
067ffa5c 6104eb7d System.Threading.ThreadPoolWorkQueue.Dispatch() [f:ddndpclrsrcBCLsystemthreadingthreadpool.cs @ 820]
067ffaac 6104e9db System.Threading._ThreadPoolWaitCallback.PerformWaitCallback() [f:ddndpclrsrcBCLsystemthreadingthreadpool.cs @ 1161]
067ffccc 7c69f036 [DebuggerU2MCatchHandlerFrame: 067ffccc]
从线程栈可以清晰地追踪到原来是 backgroundWorker1_DoWork 下的 Button 创建的,这就是问题的根源。。。
在我一百多dump的分析旅程中,这个问题真的太高频了,补充此篇真心希望能帮助这些朋友在焦虑中找到问题Control, 一毫之善,与人方便。