we know that with the help of reflection we can create instance of a class dynamically at run time and can call the method of the class very easily. so this point reflection is late binding because action is taken at run time. so i just want know reflection is faster or not.
what is the performance of reflection. is it good or bad...is it resource hungry. please discuss. thnks.
Technically speaking reflection is a performance hit. But if you're doing something that needs it then you have to use it. If you can go without it, avoid it.
EDIT
To further emphasize, reflection is neither good or bad. Its in the Framework because there's very legitimate reasons to use it. That said, 90% of the time that I see someone using reflection they're trying to do something the hard way, not knowing the easy route. Often its because they don't know about generics.
Generally, the performance of reflection is worse than when you do the same thing without reflection. But whether it is too slow for you depends on what your performance requirements are (do you need it to be fast) and what exactly are you doing.
Related
Why the designers of C# did not allow for something like this?
public readonly class ImmutableThing
{
...
}
One of the most important ways to safe multi-threading is the use of immutable objects/classes, yet there is no way to declare a class as immutable. I know I can make it immutable by proper implementation but having this enforced by class declaration would make it so much easier and safer. Commenting a class as immutable is a "door prop" solution at best.
One look at a class declaration and you would instantly know it was immutable. If you had to modify someone else's code you would know a class does not allow changes by intent. I can only see advantages here but I can't believe no one thought about this before. So why is not supported?
EDIT
Some say this is not very important feature but that does not really convince me. Multicore processors showed up because increasing performance by frequency hit a wall. Supercomputers are heavily multiprocessor machines. Parallel processing is more and more important and is one of the main ways to improve performance. The support for multithreading and parallel processing in .NET is significant (various lock types, thread pool, tasks, async calls, concurrent collections, blocking collection, parallel foreach, PLINQ and so on) and it seems to me everything that helps you write parallel code more easily gives an edge. Even if it's non trivial to implement.
Basically, because it's complicated - and as usr wrote, features need a lot of work in various ways before they're ready to ship. (It's easy being an armchair language designer - I'm sure it's incredibly difficult to really do it, in a language with millions of developers with critical code bases which can't be broken by changes.)
It's tricky for a compiler to verify that a type is visibly-immutable without being overly restrictive in some cases. As an example, String is actually mutable within mscorlib, but the code of other types (e.g. StringBuilder) has been written very carefully to avoid the outside world ever seeing that mutability.
Eric Lippert has written a lot on immutability - it's a complex topic which would/will need a lot of work to turn into a practical language feature. It's also quite hard to retrofit onto a language and framework which didn't have it to start with. I'd love C# to at least make it easier to write immutable types, and I suspect the team has spent quite a while thinking about it - whether they'll ever be happy enough with their ideas to turn it into a production language feature is a different matter.
Features need to be designed, implemented, tested, documented, deployed and supported. That's why we get the most important features first, and the less important ones late or never.
Your proposal is ok, but there is an easy workaround (as you said). Therefore it is not an "urgent" feature.
There is also a thing called representational immutability where state mutations inside the object are allowed but are never made visible to the outside. Example: a lazily-calculated field. This would not be possible under your proposal because the compiler could never prove the class to be immutable to the outside, although its field are routinely written to.
Are there any tools that can find any private functions without any references? (Redundant functions)
Reason being, that a function may have been created and called from a couple of areas, but as the project expands and grows, these two calls may have been removed and swapped with a better alternative. But the method may still remain. I was wondering if there were any handy tools that would look through the code, spotting private functions and checking if they have any references, if not, inform the user of the situation.
It wouldn't be too tricky to create one myself, but I was wondering if there were any accessible apps that could do this with the files containing the code?
My code is in c#, but I can imagine that this question covers a variety of coding languages.
ReSharper does the job.
If your code has Unit Tests (it does, right? ;-) then running NCover will allow you to identify methods that aren't being called from anywhere. If you haven't got any unit tests then it's a good excuse to use for starting to build them.
In the general case, I'd suspect that code coverage tools are a good fit in most languages.
Eclipse does it automatically for Java, not sure if you can have same thing for C#.
Another question might even be "Does the c# compiler remove private methods that aren't actually used?".
My guess would be no, but you never know!
EDIT:
Actually, I think it might be hard to tell where a method is used. It might be private, but it can still be used as Event Handlers. Not impossible to check, but I'm sure that aspect would make it a little more difficult.
Are there any performance implications with using the provider pattern?
Does it rely on reflection for each instantiation or anything?
Yes, the provider model usually involves a small amount of reflection, and therefore, there is going to be a little bit of a performance hit, however, it is only in the instantiation of the provider object. Once the object is instantiated, it is accessed as normal (usually via an interface). The performance versus a hard-coded model should have very little difference, but the gain you get from the programming perspective far outweighs any performance penalty. Assuming the provider actually may change one day. If not, just hard-code it.
Providers are instanced once per app-domain. Although newing up an object via reflection is slower than doing it inline, it is still very, very fast. I would say there is no performance concern for most business apps.
I am working on an application that is about 250,000 lines of code. I'm currently the only developer working on this application that was originally built in .NET 1.1. Pervasive throughout is a class that inherits from CollectionBase. All database collections inherit from this class. I am considering refactoring to inherit from the generic collection List instead. Needless to say, Martin Fowler's Refactoring book has no suggestions. Should I attempt this refactor? If so, what is the best way to tackle this refactor?
And yes, there are unit tests throughout, but no QA team.
Don't. Unless you have a really good business justification for putting your code base through this exercise. What is the cost savings or revenue generated by your refactor? If I were your manager I would probably advise against it. Sorry.
How exposed is CollectionBase from the inherited class?
Are there things that Generics could do better than CollectionBase?
I mean this class is heavily used, but it is only one class. Key to refactoring is not disturbing the program's status quo. The class should always maintain its contract with the outside world. If you can do this, it's not a quarter million lines of code you are refactoring, but maybe only 2500 (random guess, I have no idea how big this class is).
But if there is a lot of exposure from this class, you may have to instead treat that exposure as the contract and try and factor out the exposure.
If you are going to go through with it, don't use List< T >. Instead, use System.Collections.ObjectModel.Collection< T >, which is more of a spirtual succesor to CollectionBase.
The Collection<T> class provides protected methods that can be used to customize its behavior when adding and removing items, clearing the collection, or setting the value of an existing item. If you use List<T> there's no way to override the Add() method to handle when someone ads to the collection.
250,000 Lines is alot to refactor, plus you should take into account several of the follow:
Do you have a QA department that will be able to QA the refactored code?
Do you have unit tests for the old code?
Is there a timeframe that is around the project, i.e. are you maintaining the code as users are finding bugs?
if you answered 1 and 2 no, I would first and foremost write unit tests for the existing code. Make them extensive and thorough. Once you have those in place, branch a version, and start refactoring. The unit tests should be able to help you refactor in the generics in correctly.
If 2 is yes, then just branch and start refactoring, relying on those unit tests.
A QA department would help a lot as well, since you can field them the new code to test.
And lastly, if clients/users are needing bugs fixed, fix them first.
I think refactoring and keeping your code up to date is a very important process to avoid code rot/smell. A lot of developers suffer from either being married to their code or just not confident enough in their unit tests to be able to rip things apart and clean it up and do it right.
If you don't take the time to clean it up and make the code better, you'll regret it in the long run because you have to maintain that code for many years to come, or whoever takes over the code will hate you. You said you have unit tests and you should be able to trust those tests to make sure that when you refactor the code it'll still work.
So I say do it, clean it up, make it beautiful. If you aren't confident that your unit tests can handle the refactor, write some more.
I agree with Thomas.
I feel the question you should always ask yourself when refactoring is "What do I gain by doing this vs doing something else with my time?" The answer can be many things, from increasing maintainability to better performance, but it will always come at the expense of something else.
Without seeing the code it's hard for me to tell, but this sounds like a very bad situation to be refactoring in. Tests are good, but they aren't fool-proof. All it takes is for one of them to have a bad assumption, and your refactor could introduce a nasty bug. And with no QA to catch it, that would not be good.
I'm also personally a little leary of massive refactors like this. Cost me a job once. It was my first job outside of the government (which tends to be a little more forgiving, once you get 'tenure' it's damn hard to get fired) and I was the sole web programmer. I got a legacy ASP app that was poorly written dropped in my lap. My first priority was to get the darn thing refactored into something less...icky. My employer wanted the fires put out and nothing more. Six months later I was looking for work again :p Moral of this story: Check with your manager first before embarking on this.
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How costly is .NET reflection?
I am currently in a programming mentality that reflection is my best friend. I use it a lot for dynamic loading of content that allows "loose implementation" rather than strict interfaces, as well as a lot of custom attributes.
What is the "real" cost to using reflection?
Is it worth the effort for frequently reflected types to have cached reflection, such as our own pre-LINQ DAL object code on all the properties to table definitions?
Would the caching memory footprint outwieght the reflection CPU usage?
Reflection requires a large amount of the type metadata to be loaded and then processed. This can result in a larger memory overhead and slower execution. According to this article property modification is about 2.5x-3x slower and method invocation is 3.5x-4x slower.
Here is an excellent MSDN article outlining how to make reflection faster and where the overhead is. I highly recommend reading if you want to learn more.
There is also an element of complexity that reflection can add to the code that makes it substantially more confusing and hence difficult to work with. Some people, like Scott Hanselman believe that by using reflection you often make more problems than you solve. This is especially the case if your teams is mostly junior devs.
You may be better off looking into the DLR (Dynamic Language Runtime) if you need alot of dynamic behaviour. With the new changes coming in .NET 4.0 you may want to see if you can incorporate some of it into your solution. The added support for dynamic from VB and C# make using dynamic code very elegant and creating your own dynamic objects fairly straight forward.
Good luck.
EDIT: I did some more poking around Scott's site and found this podcast on reflection. I have not listened to it but it might be worth while.
There are lots of things you can do to speed up reflection. For example, if you are doing lots of property-access, then HyperDescriptor might be useful.
If you are doing a lot of method-invoke, then you can cache methods to typed delegates using Delegate.CreateDelegate - this then does the type-checking etc only once (during CreateDelegate).
If you are doing a lot of object construction, then Delegate.CreateDelegate won't help (you can't use it on a constructor) - but (in 3.5) Expression can be used to do this, again compiling to a typed delegate.
So yes: reflection is slow, but you can optimize it without too much pain.
With great power comes great responsibility.
As you say, reflection has costs associated with it, and depending on how much reflection you do it can slow the application down significantly.
One of the very approrpiate places to use it is for IoC (Inversion of Control) since, depending on the size of your application, would probably have more benefits than not.
Thanks for the great links and great comments, especially on the part of the Jr Devs, that hit it right on the money.
For us it is easier for our junior developers to do this:
[TableName("Table")]
public class SomeDal : BaseDal
{
[FieldName("Field")]
public string Field
}
rather than some larger impelementations of DAL. This speeds up their building of the DAL objects, while hiding all the internal workings for the senior developers to gut out.
Too bad LINQ didn't come out earlier, I feel at times we wrote half of it.
One thing that can sometimes bite you when using reflection is not updating calls using reflection when doing refactoring. Tools like resharper will prompt you to update comments and strings when you change a method name, so you can catch most of them that way, but when you're calling methods that have been dynamically generated or the method name has been dynamically generated you might miss something.
The only solution is good documentation and thorough unit testing.