I have worked with c# code for past 4 years, but recently I went through a scenario which I never pass through. I got a damn project to troubleshoot the "Index out of range error". The code looks crazy and all the unnecessary things were there but it's been in production for past 3 years I just need to fix this issue. Coming to the problem.
class FilterCondition
{
.....
public string DataSetName {get; set;}
public bool IsFilterMatch()
{
//somecode here
Dataset dsDataSet = FilterDataSources.GetDataSource(DataSetName); // Static class and Static collection
var filter = "columnname filtername"
//some code here
ds.defaultview.filter= filter;
var isvalid = ds.defaultView.rowcount > 0? true : false;
return isValid;
}
}
// from a out side function they put this in a parallel loop
Parallel.ForEach()
{
// at some point its calling
item.IsFiltermatch();
}
When I debug, dsDataSet I saw that dsDataSet is modified my multiple threads. That's why race condition happens and it failed to apply the filter and fails with index out of Range.
My question here is, my method is Non-static and thread safe, then how this race condition happening since dsDataset is a local variable inside my member function. Strange, I suspect something to do with Parallel.Foreach.
And when I put a normal lock over there issue got resolved, for that also I have no answer. Why should I put lock on a non-static member function?
Can anyone give me an answer for this. I am new to the group. if I am missing anything in the question please let me know. I can't copy the whole code since client restrictions there. Thanks for reading.
Because it's not thread safe.
You're accessing a static collection from multiple threads.
You have a misconception about local variables. Although the variable is local, it's pointing at an object which is not.
What you should do is add a lock around the places where you read and write to the static collection.
Problem: the problem lies within this call
FilterDataSources.GetDataSource(DataSetName);
Inside this method you are writing to a resource that is shared.
Solution:
You need to know which field is being written here and need to implement locking on it.
Note: If you could post your code for the above method we would be in a better position to help you.
I believe this is because of specific (not-stateless, not thread safe, etc) implementation of FilterDataSources.GetDataSource(DataSetName), even by a method call it seems this is a static method. This method can do different things even return cached DataSet instance, intercept calls to a data set items, return a DataSet wrapper so you are working with a wrapper not a data set, so a lot of stuff can be there. If you want to fine let's say "exact line of code" which causes this please show us implementation of GetDataSource() method and all underlying static context of FilterDataSource class (static fields, constructor, other static methods which are being called by GetDataSource() if such exists...)
Suppose I have a method like this:
public void MyCoolMethod(ref bool scannerEnabled)
{
try
{
CallDangerousMethod();
}
catch (FormatException exp)
{
try
{
//Disable scanner before validation.
scannerEnabled = false;
if (exp.Message == "FormatException")
{
MessageBox.Show(exp.Message);
}
}
finally
{
//Enable scanner after validation.
scannerEnabled = true;
}
}
And it is used like this:
MyCoolMethod(ref MyScannerEnabledVar);
The scanner can fire at any time on a separate thread. The idea is to not let it if we are handling an exception.
The question I have is, does the call to MyCoolMethod update MyScannerEnabledVar when scannerEnabled is set or does it update it when the method exits?
Note: I did not write this code, I am just trying to refactor it safely.
You can think of a ref as making an alias to a variable. It's not that the variable you pass is "passed by reference", it's that the parameter and the argument are the same variable, just with two different names. So updating one immediately updates the other, because there aren't actually two things here in the first place.
As SLaks notes, there are situations in VB that use copy-in-copy-out semantics. There are also, if I recall correctly, rare and obscure situations in which expression trees may be compiled into code that does copy-in-copy-out, but I do not recall the details.
If this code is intended to update the variable for reading on another thread, the fact that the variable is "immediately" updated is misleading. Remember, on multiple threads, reads and writes can be observed to move forwards and backwards in time with respect to each other if the reads and writes are not volatile. If the intention is to use the variable as a cross-thread communications mechanism them use an object actually designed for that purpose which is safe for that purpose. Use some sort of wait handle or mutex or whatever.
It gets updated live, as it is assigned inside the method.
When you pass a parameter by reference, the runtime passes (an equivalent to) a pointer to the field or variable that you referenced. When the method assigns to the parameter, it assigns directly to whatever the reference is pointing to.
Note, by the way, that this is not always true in VB.
Yes, it will be set when the variable is set within the method. Perhaps it would be best to return true or false whether the scanner is enabled rather than pass it in as a ref arg
The situation calls for more than a simple refactor. The code you posted will be subject to race conditions. The easy solution is to lock the unsafe method, thereby forcing threads to hop in line. The way it is, there's bound to be some bug(s) in the application due to this code, but its impossible to say what exactly they are without knowing a lot more about your requirements and implementation. I recommend you proceed with caution, a mutex/lock is an easy fix, but may have a great impact on performance. If this is a concern for you, then you all should review a better thread safe solution.
I'm a little confused about when exactly my Property is being initialized.
Suppose I have a property declared like this:
private Dictionary<string, Dictionary<string,string>> MessageLookup
{
get
{
return messages ?? doSomething();
}
}
The doSomething method populates the messages Dictionary and returns it.
My question is, when is this code run?
If I place a breakpoint into the doSomething code, it isn't hit, but the MessageLookup property is holding data (this is the only place it is initialized) when I view it in the debugger.
Is this code run at construction? does the debugger run it automatically when I hover over the variable name? If so, why isn't the breakpoint hit?
That code is run whenever anyone refers to the property, and not before.
If you use the debugger, you'll see it because the debugger tries to fetch property values automatically (so you can see the state of the object). I don't know whether the debugger ignores breakpoints while it's evaluating properties for itself - that would explain everything.
Try running your code not in a debugger, and make some code access your property:
var lookup = someObject.MessageLookup;
Make doSomething() dump a stack trace and you'll see what's going on.
It is run when your property is first evaluated. No background stuff going on.
I'm guessing you're not seeing this because you use Quickwatch to inspect your object. At that point it will get executed and your breakpoint will be skipped.
Property getters (and ToString() for that matter) are assumed to be pure, which basically means evaluating it has no side effects. You should rewrite the code to adhere to that assumption or you'll face nasty consequences. If must use lazy initialization at access time, use a GetMessageLookup() method instead.
In Visual Studio, is there any way to make the debugger break whenever a certain file (or class) is entered? Please don't answer "just set a breakpoint at the beginning of every method" :)
I am using C#.
Macros can be your friend. Here is a macro that will add a breakpoint to every method in the current class (put the cursor somewhere in the class before running it).
Public Module ClassBreak
Public Sub BreakOnAnyMember()
Dim debugger As EnvDTE.Debugger = DTE.Debugger
Dim sel As EnvDTE.TextSelection = DTE.ActiveDocument.Selection
Dim editPoint As EnvDTE.EditPoint = sel.ActivePoint.CreateEditPoint()
Dim classElem As EnvDTE.CodeElement = editPoint.CodeElement(vsCMElement.vsCMElementClass)
If Not classElem Is Nothing Then
For Each member As EnvDTE.CodeElement In classElem.Children
If member.Kind = vsCMElement.vsCMElementFunction Then
debugger.Breakpoints.Add(member.FullName)
End If
Next
End If
End Sub
End Module
Edit: Updated to add breakpoint by function name, rather than file/line number. It 'feels' better and will be easier to recognise in the breakpoints window.
You could start by introducing some sort of Aspect-Oriented Programming - see for instance
this explanation - and then put a breakpoint in the single OnEnter method.
Depending on which AOP framework you choose, it'd require a little decoration in your code and introduce a little overhead (that you can remove later) but at least you won't need to set breakpoints everywhere. In some frameworks you might even be able to introduce it with no code change at all, just an XML file on the side?
Maybe you could use an AOP framework such as PostSharp to break into the debugger whenever a method is entered. Have a look at the very short tutorial on this page for an example, how you can log/trace whenever a method is entered.
Instead of logging, in your case you could put the Debugger.Break() statement into the OnEntry-handler. Although, the debugger would not stop in your methods, but in the OnEntry-handler (so I'm not sure if this really helps).
Here's a very basic sample:
The aspect class defines an OnEntry handler, which calls Debugger.Break():
[Serializable]
public sealed class DebugBreakAttribute : PostSharp.Laos.OnMethodBoundaryAspect
{
public DebugBreakAttribute() {}
public DebugBreakAttribute(string category) {}
public string Category { get { return "DebugBreak"; } }
public override void OnEntry(PostSharp.Laos.MethodExecutionEventArgs eventArgs)
{
base.OnEntry(eventArgs);
// debugger will break here. Press F10 to continue to the "real" method
System.Diagnostics.Debugger.Break();
}
}
I can then apply this aspect to my class, where I want the debugger to break whenever a method is called:
[DebugBreak("DebugBreak")]
public class MyClass
{
public MyClass()
{
// ...
}
public void Test()
{
// ...
}
}
Now if I build and run the application, the debugger will stop in the OnEntry() handler whenever one of the methods of MyClass is called. All I have to do then, is to press F10, and I'm in the method of MyClass.
Well, as everyone is saying, it involves setting a breakpoint at the beginning of every method. But you're not seeing the bigger picture.
For this to work at all, a breakpoint has to be set at the beginning of every method. Whether you do it manually, or the debugger does it automatically, those breakpoints must be set for this to work.
So, the question really becomes, "If there enough of a need for this functionality, that it is worth building into the debugger an automatic means of setting all those breakpoints?". And the answer is, "Not Really".
This feature is implemented in VS for native C++. crtl-B and specify the 'function' as "Classname::*", this sets a breakpoint at the beginning of every method on the class. The breakpoints set are grouped together in the breakpoints window (ctrl-alt-B) so they can be enabled, disabled, and removed as a group.
Sadly the macro is likely the best bet for managed code.
This works fine in WinDbg:
bm exename!CSomeClass::*
(Just to clarify, the above line sets a breakpoint on all functions in the class, just like the OP is asking for, without resorting to CRT hacking or macro silliness)
You could write a Visual Studio macro that obtained a list of all of the class methods (say, by reading the .map file produced alongside the executable and searching it for the proper symbol names (and then demangling those names)), and then used Breakpoints.add() to programmatically add breakpoints to those functions.
System.Diagnostics.Debugger.Break();
(at the beginning of every method)
No. Or rather, yes, but it involves setting a breakpoint at the beginning of every method.
Use Debugger.Break(); (from the System.Diagnostics namespace)
Put it at the top of each function you wish to have "broken"
void MyFunction()
{
Debugger.Break();
Console.WriteLine("More stuff...");
}
Isn't the simplest method to get closest to this to simply set a break point in the constructor (assuming you have only one - or each of them in the case of multiple constructors) ?
This will break into debugging when the class is first instantiated in the case of a non-static constructor, and in the case of a static constructor/class, you'll break into debugging as soon as Visual Studio decides to initialize your class.
This certainly prevents you from having to set a breakpoint in every method within the class.
Of course, you won't continue to break into debugging on subsequent re-entry to the class's code (assuming you're using the same instantiated object the next time around), however, if you re-instantiate a new object each time from within the calling code, you could simulate this.
However, in conventional terms, there's no simple way to set a single break point in one place (for example) and have it break into debugging every time a class's code (from whichever method) is entered (as far as I know).
Assuming that you're only interested in public methods i.e. when the class methods are called "from outside", I will plug Design by Contract once more.
You can get into the habit of writing your public functions like this:
public int Whatever(int blah, bool duh)
{
// INVARIANT (i)
// PRECONDITION CHECK (ii)
// BODY (iii)
// POSTCONDITION CHECK (iv)
// INVARIANT (v)
}
Then you can use the Invariant() function that you will call in (i) and set a breakpoint in it. Then inspect the call stack to know where you're coming from. Of course you will call it in (v), too; if you're really interested in only entry points, you could use a helper function to call Invariant from (i) and another one from (v).
Of course this is extra code but
It's useful code anyway, and the structure is boilerplate if you use Design by Contract.
Sometimes you want breakpoints to investigate some incorrect behaviour eg invalid object state, in that case invariants might be priceless.
For an object which is always valid, the Invariant() function just has a body that returns true. You can still put a breakpoint there.
It's just an idea, it admittedly has a footstep, so just consider it and use it if you like it.
Joel, the answer seems to be "no". There isn't a way without a breakpoint at every method.
To remove the breakpoints set by the accepted answer add another macro with the following code
Public Sub RemoveBreakOnAnyMember()
Dim debugger As EnvDTE.Debugger = DTE.Debugger
Dim bps As Breakpoints
bps = debugger.Breakpoints
If (bps.Count > 0) Then
Dim bp As Breakpoint
For Each bp In bps
Dim split As String() = bp.File.Split(New [Char]() {"\"c})
If (split.Length > 0) Then
Dim strName = split(split.Length - 1)
If (strName.Equals(DTE.ActiveDocument.Name)) Then
bp.Delete()
End If
End If
Next
End If
End Sub
Not that I'm aware of. The best you can do is to put a breakpoint in every method in the file or class. What are you trying to do? Are you trying to figure out what method is causing something to change? If so, perhaps a data breakpoint will be more appropriate.
You could write a wrapper method through which you make EVERY call in your app. Then you set a breakpoint in that single method. But... you'd be crazy to do such a thing.
You could put a memory break point on this, and set it to on read. I think there should be a read most of the time you call a member function. I'm not sure about static functions.
you can use the following macro:
#ifdef _DEBUG
#define DEBUG_METHOD(x) x DebugBreak();
#else
#define DEBUG_METHOD(x) x
#endif
#include <windows.h>
DEBUG_METHOD(int func(int arg) {)
return 0;
}
on function enter it will break into the debugger
IF this is C++ you are talking about, then you could probably get away with, (a hell of a lot of work) setting a break point in the preamble code in the CRT, or writing code that modifies the preamble code to stick INT 3's in there only for functions generated from the class in question... This, BTW, CAN be done at runtime... You'd have to have the PE file that's generated modify itself, possibly before relocation, to stick all the break's in there...
My only other suggestion would be to write a Macro that uses the predefined macro __FUNCTION__, in which you look for any function that's part of the class in question, and if necessary, stick a
__asm { int 3 }
in your macro to make VS break... This will prevent you from having to set break points at the start of every function, but you'd still have to stick a macro call, which is a lot better, if you ask me. I think I read somewhere on how you can define, or redefine the preamble code that's called per function.. I'll see what I can find.
I would think I similar hack could be used to detect which FILE you enter, but you STILL have to place YOUR function macro's all over your code, or it will never get called, and, well, that's pretty much what you didn't want to do.
If you are willing to use a macro then the accepted answer from this question
Should be trivially convertible to you needs by making the search function searching for methods, properties and constructors (as desired), there is also quite possibly a way to get the same information from the the ide/symbols which will be more stable (though perhaps a little more complex).
You can use Debugger.Launch() and Debugger.Break() in the assembly System.Diagnostics
Files have no existence at runtime (consider that partial classes are no different -- in terms of code -- from putting everything in a single file). Therefore a macro approach (or code in every method) is required.
To do the same with a type (which does exist at runtime) may be able to be done, but likely to be highly intrusive, creating more potential for heisenbugs. The "easiest" route to this is likely to be making use of .NET remoting's proxy infrastructure (see MOQ's implementation for an example of using transparent proxy).
Summary: use a macro, or select all followed by set breakpoint (ctrl-A, F9).
Mad method using reflection. See the documentation for MethodRental.SwapMethodBody for details. In pseudocode:
void SetBreakpointsForAllMethodsAndConstructorsInClass (string classname)
{
find type information for class classname
for each constructor and method
get MSIL bytes
prepend call to System.Diagnostics.Debugger.Break to MSIL bytes
fix up MSIL code (I'm not familiar with the MSIL spec. Generally, absolute jump targets need fixing up)
call SwapMethodBody with new MSIL
}
You can then pass in classname as a runtime argument (via the command line if you want) to set breakpoints on all methods and constructors of the given class.