This is a bit of a weird issue as I cannot reproduce it. I have two customers capable of reproducing this issue who have sent me WER logs.
I have a C# application which queues work items and executes them in the background. In a very small percentage of machines, immediately upon trying to execute the first line of the worker thread, it immediately throws an NPE.
Ausnahmeinformationen: System.NullReferenceException
bei magicsim.SimcPreloaderData+<>c__DisplayClass16_0.<LoadArmoryData>b__0(System.Object)
bei System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(System.Object)
bei System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
bei System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext, System.Threading.ContextCallback, System.Object, Boolean)
bei System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
bei System.Threading.ThreadPoolWorkQueue.Dispatch()
bei System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()
The WER information is very interesting as well.
Problemsignatur:
P1: magicsim.exe
P2: 2.2.0.2
P3: 5b7df04c
P4: magicsim
P5: 2.2.0.2
P6: 5b7df04c
P7: 29b
P8: fb
P9: System.NullReferenceException
P10:
So this is in method 29b, trying to hit IL line fb.
Using ILDASM I can validate the location of this problem signature matches the stack trace (SimcPreloaderData)
Method #2 (0600029b)
-------------------------------------------------------
MethodName: <LoadArmoryData>b__0 (0600029B)
Flags : [Assem] [HideBySig] [ReuseSlot] (00000083)
RVA : 0x0000d338
ImplFlags : [IL] [Managed] (00000000)
CallCnvntn: [DEFAULT]
hasThis
ReturnType: Void
1 Arguments
Argument #1: Object
1 Parameters
(1) ParamToken : (0800020f) Name : _ flags: [none] (00000000)
In ILSpy, I can see the following structure of the above method:
.method public hidebysig
instance void LoadArmoryData (
string simcString
) cil managed
{
// Method begins at RVA 0x7b4d
// Code size 48 (0x30)
.maxstack 8
IL_0000: newobj instance void magicsim.SimcPreloaderData/'<>c__DisplayClass16_0'::.ctor()
IL_0005: dup
IL_0006: ldarg.0
IL_0007: stfld class magicsim.SimcPreloaderData magicsim.SimcPreloaderData/'<>c__DisplayClass16_0'::'<>4__this'
IL_000c: dup
IL_000d: ldarg.1
IL_000e: stfld string magicsim.SimcPreloaderData/'<>c__DisplayClass16_0'::simcString
IL_0013: ldarg.0
IL_0014: ldstr "Acquiring SimC Executable"
IL_0019: call instance void magicsim.SimcPreloaderData::set_Label(string)
IL_001e: ldftn instance void magicsim.SimcPreloaderData/'<>c__DisplayClass16_0'::'<LoadArmoryData>b__0'(object)
IL_0024: newobj instance void [mscorlib]System.Threading.WaitCallback::.ctor(object, native int)
IL_0029: call bool [mscorlib]System.Threading.ThreadPool::QueueUserWorkItem(class [mscorlib]System.Threading.WaitCallback)
IL_002e: pop
IL_002f: ret
} // end of method SimcPreloaderData::LoadArmoryData
There is clearly no IL_00fb command to execute, hence the NPE and lack of a reference of where specifically inside LoadArmoryData this was happening (besides the fact that it simply was). The only thing I can surmise from the above is that for some reason, multithreading is going errant and trying to access an instruction that does not exist.
I do not know of why this would happen and have ruled out antivirus and permissions interferences.
Edit: For further reference, the full method.
public void LoadArmoryData(String simcString)
{
SimC simc;
Label = "Acquiring SimC Executable";
ThreadPool.QueueUserWorkItem((_) =>
{
try
{
simc = SimCManager.AcquireSimC();
}
catch (Exception e)
{
MessageBox.Show("Could not acquire SimC because of an Exception: " + e.Message, "Error", MessageBoxButton.OK, MessageBoxImage.Error);
App.Current.Dispatcher.Invoke(() =>
{
PreloadingFailed(this, new EventArgs());
});
return;
}
Label = "Generating SimC Profile";
Regex nameRegex = new Regex("(warrior|paladin|hunter|rogue|priest|deathknight|shaman|mage|warlock|monk|druid|demonhunter)+=\"?([^\r\n\"]+)\"?");
String name = nameRegex.Match(simcString).Groups[2].Value;
String text = simcString + "\nsave=./characters/" + name + ".simc";
try
{
if (!Directory.Exists("characters"))
{
Directory.CreateDirectory("characters");
}
if (File.Exists("characters/" + name))
{
File.Delete("characters/" + name);
}
File.WriteAllText("characters/" + name + ".simc", text);
}
catch (UnauthorizedAccessException e)
{
MessageBox.Show("Could not write character profile due to a permissions issue. Please retry, running as Administrator." + e.Message, "Error", MessageBoxButton.OK, MessageBoxImage.Error);
App.Current.Dispatcher.Invoke(() =>
{
PreloadingFailed(this, new EventArgs());
});
return;
}
if (simc.RunSim("characters/" + name + ".simc"))
{
Label = "SimC Profile Generated";
charName = name;
App.Current.Dispatcher.Invoke(() =>
{
PreloadingComplete(this, new EventArgs());
});
}
else
{
Label = "Failed to Generate Profile";
MessageBox.Show("Failed to generate profile. Please check your input and try again.", "Error", MessageBoxButton.OK, MessageBoxImage.Error);
App.Current.Dispatcher.Invoke(() =>
{
PreloadingFailed(this, new EventArgs());
});
}
});
}
EDIT 2 (For completeness):
In fact, 29b refers to b__0, not LoadArmoryData.
If you look at the correct method in ILSpy you see the following sequence of commands which implies the clear issue and potential solution.
// string contents = simcString + "\nsave=./characters/" + value + ".simc";
IL_00ce: ldarg.0
IL_00cf: ldfld string magicsim.SimcPreloaderData/'<>c__DisplayClass16_0'::simcString
IL_00d4: ldstr "\nsave=./characters/"
IL_00d9: ldloc.0
IL_00da: ldstr ".simc"
IL_00df: call string [mscorlib]System.String::Concat(string, string, string, string)
IL_00e4: stloc.1
// File.WriteAllText("characters/" + value + ".simc", contents);
IL_00e5: ldstr "characters/"
IL_00ea: ldloc.0
IL_00eb: ldstr ".simc"
IL_00f0: call string [mscorlib]System.String::Concat(string, string, string)
IL_00f5: ldloc.1
IL_00f6: call void [mscorlib]System.IO.File::WriteAllText(string, string)
// if (simc.RunSim("characters/" + value + ".simc"))
IL_00fb: ldarg.0
IL_00fc: ldfld class magicsim.SimC magicsim.SimcPreloaderData/'<>c__DisplayClass16_0'::simc
IL_0101: ldstr "characters/"
IL_0106: ldloc.0
IL_0107: ldstr ".simc"
IL_010c: call string [mscorlib]System.String::Concat(string, string, string)
IL_0111: callvirt instance bool magicsim.SimC::RunSim(string)
// (no C# code)
IL_0116: brfalse.s IL_0163
I think the analysis in the question is flawed (e.g. the exception is coming from <LoadArmoryData>b__0(System.Object), which represent a lambda expression in LoadArmoryData whose signature expects an object parameter; but you are looking at the IL for LoadArmoryData, which is a method whose signature expects a string parameter).
This is just a straightforward NullReferenceException, probably coming from nameRegex.Match(simcString).Groups[2].Value; when the Regex doesn't match.