Basically, the question is:
Do the Exceptions in C# affect the performance a lot? Is it better to avoid Exceptions rethrow? If i generate an exception in my code, does it affect a performance?
Sorry for the sillines of the question itself
If you're worried about exception performance, you're using them wrong.
But yes, exceptions do affect performance.
Raising an exception is an expensive operation in C# (compared to other operations in C#) but not enough that I would avoid doing it.
I agree with Jared, if your application is significantly slower because of raising and throwing exceptions, I would take a look at your overall strategy. Something can probably be refactored to make exception handling more efficient rather than dismissing the concept of raising exceptions in code.
Microsoft's Design Guidelines for Developing Class Libraries is a very valuable resource. Here is a relevant article:
Exceptions and Performance
I would also recommend the Framework Design Guidelines book from Microsoft Press. It has a lot of the information from the Design Guidelines link, but it is annotated by people with MS, and Anders Hejlsberg, himself. It gives a lot of insight into the "why" and "how" of the way things are.
running code through a try/catch statement does not affect performance at all. The only performance hit comes if an exception is thrown ... because then the runtime has to unwind the stack and gather other information in order to populate the exception object.
What most other folks said, plus:
Don't use exceptions as part of the programming flow. In other words, don't throw an exception for something like, account.withdrawalAmount > account.balance. That is a business case.
The other biggie to look out for regarding performance is swallowing exceptions. It's a slippery slope, and once you start allowing your app to swallow exceptions, you start doing it everywhere. Now you may be allowing your app to throw exceptions that you don't know about because you are swallowing them, your performance suffers and you don't know why.
This is not silly just I've seen it somewhere else also on SO.
The exceptions occur well, when things are really exceptional. Most of the time you re-throw the exception (may after logging) when there are not many chances of recovering from it. So it should not bother you for normal course of execution of program.
Exceptions as its name implies are intended to be exceptional. Hence you can't expect them to have been an important target for optimisation. More often then not they don't perform well since they have other priorites such as gathering detailed info about what went wrong.
Exceptions in .NET do affect performance. This is the reason why they should be used only in exceptional cases.
Related
I have a C# application..I continuously get a null reference exception..I manage to catch this exception and log it..But i doubt if this exception will affect the performance of my application..Please note that i am not trying to avoid the exception instead i need to know if this exception affects the performance of my application if it is continuously fired .
If you're getting a NullReferenceException, you should fix it rather than catching it. You should only ever catch it if it occurs in code in a way that you cannot fix (e.g. a broken third party library). A NullReferenceException always indicates a programming error somewhere.
As for performance - it depends on what you mean by "continuously". Exceptions can be horribly expensive if they're thrown when nothing's really wrong - they're fine when used properly. How many are you seeing per second, for example? Note that when running in a debugger, exceptions are often much more expensive than they would be when a debugger isn't attached.
As ever, when you're worried about performance, you should test the performance, so you can use hard data to make decisions.
It depends where you handle the exceptions and how often they happen. There is a good article on CodeProject regarding exceptions and performance, I suggest you read it.
Yes it affects it depend upon the frequency of it .
For further info please refer Link and it may also help you Link
Exceptions have been designed to alter performances to a minimum when they are not thrown : adding a try/catch block should have very limited impact to your application performances.
Therefore, I'd recommand to add as many try/catch blocks as required to catch any exception IN THE RIGHT LEVEL.
However, throwing and catching an exception may be very expensive. Application has to switch contexts, dispose any element in using blocks... And that's why I agree with #Ramhound : you ought to fix the exception rather than catching it.
In a high performance C# program (where performance is the no1 concern), what sacrifices would be made to the code?
For example, how would exception handling change (less exceptions thrown/same no of exceptions caught?)?
I ask as I used to work in a monitoring company where a collector was written.
Thanks
Usually you should Throw exceptions only when is strictly needed as it could leads the performance
What’s the alternative to exception handling then?
You write code to check the input values and return values of each one of your methods and pass a return value back up to the caller.
http://codebetter.com/raymondlewallen/2004/12/13/performance-issues-with-exception-handling/
http://www.codeproject.com/Articles/11265/Performance-implications-of-Exceptions-in-NET
You can measure performance by yourself and see how much exception handling slows the code down. Generally, if an exception is thrown, it is very wasteful, but if no exception is thrown, try ... catch slows the code only by a bit.
Another point: Linq is slower that simple iteration.
Exceptions should only be thrown in exceptional cases. They should not be used for flow control. A good goal is to be able to run your application under the debugger with normal use and exceptions should not be thrown.
If that's the case, in a high performance app, the cost of exceptions shouldn't be as much of a concern if they are truly exceptional.
Exception handling is slow. By default, Exception instances are, what the name implies, an exception.
However if you expect them to occure a lot, you can decide to throw less Exception objects and handle the logical exceptions in another way. In other words, they became expected.
In the case they actually are unexpected, you can try to handle them earlier in the stack. A solution would be by using bool or enum retVals. Rethrowing exceptions causes loss of performance.
Exceptions are the best way to handle exceptional circumstances. If some condition is expected then check for it with a conditional statement like if.
Apart from these generic rules, how much maintainability are you willing to sacrafice for performance? You could always write the code in assembler.
I just found in a project:
try
{
myLabel.Text = school.SchoolName;
}
catch
{
myPanel.Visible = false;
}
I want to talk to the developer than wrote this, saying that incurring the null exception (because school might theoretically be null, not myLabel) would virtually make the computer beep three times and sleep for two seconds. However, I wonder if I'm misremembering the rule about that. Obviously, this isn't the intended use for try/catch, but is this bad because it defies intention, or bad because of performance considerations? I feel like it's just bad, but I want to say more than "that's really bad".
You should not use exceptions for control flow simply because it is bad design. It doesn't make sense. Exceptions are for exceptional cases, not for normal flow. Performance probably won't be an issue in this situation because for most modern applications on modern hardware, you could throw exceptions all day long and the user wouldn't notice a performance hit. However, if this is a high performance application processing a lot of data or doing a lot of some sort of work, then yes, performance would be a concern.
In my opinion this is poor because it could be made much more clear with an if statement:
if (school != null) {
myLabel.Text = school.SchoolName;
}
else {
myPanel.Visible = false;
}
That will certainly avoid using exception handling unnecessarily and make the code's meaning very obvious.
I think this is bad because it is coding against an exception for one and it will also inherit unnecessary overhead. Exceptions should only be caught if they are going to be handled in a specific way.
Exceptions should be caught specifically for Exceptional cases that you can not predict, in this case it is a simple check to see if school can be null, in fact it is expected that school might be null (since the label is set nothing). If school was null and it should not have been than it should throw its own ArgumentNullException.
Exceptions do incur runtime overhead, but it's probably negligible here. There will be a difference running in the debugger, but the built binaries should run at pretty much the same speed.
Tell your developer that any chimp can make code the machine can read. Good code is written for human beings, not machines. If a null exception is the only thing you're worried about, then it's probably a bug in the user's code -- noone should ever try to assign null to anything that way. Use an Assert() statement instead.
You are absolutely right that this is bad. It is bad because it defies intention and because it hurts performance.
I realize there is room for different programming styles, but personally, I think that even though this works, and I can see what the code is attempting to do, it also hurts readability and code clarity, making it that much more difficult for the maintenance programmers to follow. An if statement is much more appropriate here.
Throwing exceptions does have a negative impact on performance, see http://msdn.microsoft.com/en-us/library/ms229009(VS.80).aspx
I never like using exceptions for flow control. Exceptions are expensive, and it is difficult to determine what the actual flow of a program with exceptions being thrown to reach other places in code. To me this is like using GoTo. This doesn't mean that you should avoid exceptions, but rather an exception should be just that, an exception to what should normally happen in the program.
I think a worse part of the code, is that it's not even doing anything with the exception. There is no logging or even an explanation as to why the exception is being thrown.
I agree with everyone here--it's a horrible idea.
There are a few cases in Java (I think they are mostly gone now, but there may still be some in external libraries) where you were required to catch an exception for certain "non-exception" cases.
In general, when writing library code (well, any class actually), avoid using exceptions for ANYTHING that could possibly be avoided. If it's possible that a name field isn't set and that should cause an exception in a write() method, be sure to add an isValid() method so that you don't actually HAVE to catch the exception around the write to know there is a problem.
(Bad Java code addendum): this "good" programming style virtually eliminates any need for checked exceptions in Java, and checked exceptions in Java are the Suck.
Java has compiler checked exceptions. When I made transition to C++, I learned it doesn't feature checked exceptions. At first, I kept using exception handling, because it's a great feature. However, after a while I abandoned it, because I got into a situation every function might throw an exception. As only a small percentage of the functions I write can throw exceptions (say some 25% at the most), I found the overhead of doing exception handling for functions that cannot throw anything unacceptable.
Because of this, I am really surprised that there are a lot of developers who prefer unchecked exceptions. Therefore, I am curious to know how they handle this problem. How do you avoid the overhead of doing unnecessary exception handling in case the language doesn't support checked exceptions?
Remark: My question equally applies to C++ and C#, and probably to all other languages that don't feature compiler checked exception handling.
Simple. You don't do exception handling in "every function that might throw" - in C++, just about every function might do so. Instead, you do it at certain key points in your application, where you can produce a sensible, application-specific diagnostic and take sensible, application-specific corrective action, although use of the RAII idiom means (as avakar points out in his answer) that there is often little corrective action to be taken.
When I first started using C# I was scared by this too. Then I found that actually, it doesn't matter very often. I very rarely find that I can catch an exception and so something useful with it anyway... almost all my exceptions bubble up to somewhere near the top of the stack anyway, where they're handled by aborting the request or whatever.
Now when I'm writing Java, I find checked exceptions intensely frustrating a lot of the time. I think there's value in there somewhere, but it introduces as many problems as it solves.
Basically, I think we haven't really got the whole error handling side of things "right" yet, but on balance I prefer the C# approach to the Java approach.
In addition to what Neil said, you should note that there is no need for try/finally (or in context of C++ try/catch/throw), because object destructors are called even if an exception is thrown.
It is easily possible to have exception-safe code with very few try statements.
For C++ specifically, the overhead pretty much goes away if you design your classes well and use RAII.
Martin York has written a wonderful example of that in this answer.
The function can stll throw an exception, yes, but if it does, it won't need to do anything special to clean up. So you only need to actually catch the exception in one place -- the function that is able to handle it and recover from the error.
If I'm writing a class library, and at some point in that library I have code to catch an exception and deal with it, then I don't want anyone using my library to know that it even happened - it should be invisible from the outside world.
However, if they have "Catch Thrown Exceptions" turned on in Visual Studio (as opposed to "Catch User Unhandled Exceptions") then the exception will be visible to them.
Is there any way to avoid this?
No. This is by design: as a developer, I run with "Catch Thrown Exceptions" turned on, so that I can see exceptions thrown in library code (and hopefully avoid them). The situation you're in applies equally to the .NET framework's own libraries too.
The best way would be to avoid throwing the exception in the first place. As a side benefit, you library code will be faster, since throwing an exception has a noticeable impact on performance (and should only be used in 'exceptional' circumstances).
The only way you can pull this off is if you put a [DebuggerHidden] attribute on the method that may throw the exception. Like others have pointed out, better to avoid the exception altogether, but this attribute will accomplish what you want.
You cannot prevent this. Someone can always attach an debuger to the process and monitor what is going on.
You could just remove the exception and provide the error handling yourself, but I would really not recommend that because it is some kind of reinventing the wheel - recreating the exception handling system.
The said applies of course only if the code throwing and the code catching the exception are far apart and quite unreleated. If they are tightly coupled, you should really check if the call can succeed and only call in this case. Always remeber that exception are intended for exceptional cases - not for normal control flow where you could check if the operation can succeed
As Tim Robinson suggests there is no way to control someone viewing exceptions thrown from your library. His answer is good so I won't rehash it.
There are a couple of posts here on SO that you may find helpful when addressing (what sounds like) using exceptions as program flow control:
Catching exceptions as expected program execution flow control?
Why are .Net programmers so afraid of exceptions?