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Closed 12 years ago.
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Performance Cost Of ‘try’
I am being told that adding a try catch block adds major performance cost in the order of 1000 times slower than without, in the example of a for loop of a million. Is this true?
Isn't it best to use try catch block as much as possible?
From MSDN site:
Finding and designing away
exception-heavy code can result in a
decent perf win. Bear in mind that
this has nothing to do with try/catch
blocks: you only incur the cost when
the actual exception is thrown. You
can use as many try/catch blocks as
you want. Using exceptions
gratuitously is where you lose
performance. For example, you should
stay away from things like using
exceptions for control flow.
Also see these related SO questions: (1) (2) (3) and (4).
I could swear there was a question like this just a few days ago, but I can't find it...
Just adding a try/catch block is unlikely to change the performance noticeably when exceptions aren't being thrown, although it may prevent a method from being inlined. (Different CLR versions have different rules around inlining; I can't remember the details.)
The real expense is when an exception is actually thrown - and even that expense is usually overblown. If you use exceptions appropriately (i.e. only in genuinely exceptional or unexpected error situations) then they're unlikely to be a significant performance hit except in cases where your service is too hosed to be considered "working" anyway.
As for whether you should use try/catch blocks as much as possible - absolutely not! You should usually only catch an exception if you can actually handle it - which is relatively rare. In particular, just swallowing an exception is almost always the wrong thing to do.
I write far more try/finally blocks (effectively - almost always via using statements) than try/catch blocks. Try/catch is sometimes appropriate at the top level of a stack, so that a service can keep processing the next request even if one fails, but otherwise I rarely catch exceptions. Sometimes it's worth catching one exception in order to wrap it in a different exception - basically translating the exception rather than really handling it.
You should definitely test claims like this (easy enough), but no, that isn't going to hurt you (it'll have a cost, but not 1000's of times).
Throwing exceptions and handling them is expensive. Having a try..catch..finally isn't bad.
Now with that said, If you are going to catch an exception, you need to have a plan for what you are going to do with it. There is no point in catching if you are just going to rethrow, and a lot of times, there's not much you can do if you get an exception.
Adding try catch blocks helps control your application from exceptions you have no control over. The performance cost comes from throwing an exception when there are other alternatives. For example throwing an exception to bail out of a routine instead of simply returning from a routine causes a significant amount of overhead, which may be completely unnecessary.
I am being told that adding a try
catch block adds major performance
cost in the order of 1000 times slower
than without, in the example of a for
loop of a million. Is this true?
Using try catch adds performance cost, but it isn't a major performance cost.
Isn't it best to use try catch block
as much as possible?
No, it is best to use try catch block when makes sense.
Why guess at the performance costs, when you can benchmark and see if it matters?
It's true that exceptions a very expensive operation. Also try..catch blocks clutter the code and make it hard to read. That said exceptions are fine for errors that should crash the application most of the time.
I always run on break on all exceptions, so as soon as an error happens it throws and I can pinpoint it fairly easy. If everyone is throwing exceptions all the time I get bad performance and I can't use the break on all exceptions, that's makes me sad.
IMO don't use exception for normal program events (like user types in a non-number and you try to parse it as a number). Use the normal program flow constructs for that (ie if).
If you use functions that may throw you make a choice. Is the error critical => crash the app. Is the error non-critical and likely => catch it (and potentially log it).
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.
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Closed 11 years ago.
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When to use try/catch blocks?
Main method code entirely inside try/catch: Is it bad practice?
When to use Try Catch blocks
Exceptions can occur about anywhere, so this made me think: should I always wrap my code in try..catch blocks?
This is for C#.
(I might be missing something fundamental here, as I'm still a newbie)
EDIT: It appears that this was indeed not a very smart question. The only thing we have learnt at school is to use try...catch to prevent crashes. What we did with the exception was showing a MessageBox to tell the user that 'something went wrong when writing this file'.
Exceptions can occur about anywhere, so this made me think: should I always wrap my code in try..catch blocks?
Good question. Here's a related question:
Axe-wielding maniacs can be just about anywhere, so: should I wear axe-resistant body armor 24 hours a day?
I am fortunate to live in a neighborhood where the number of axe-wielding maniacs is sufficiently low that I don't wear armor when I leave the house. But suppose I did not. Is the right solution to wear the armor all the time or to jail the maniacs?
If your programs throw so many exceptions that you need to be handling those exceptions everywhere, then you have a big problem. The solution to that problem is not to armor up and put exception handling everywhere. The solution to that problem is to eliminate the code that is throwing the exceptions, and if you cannot eliminate it, then isolate it to a tiny region of code that does use exception handling.
Absolutely not. Here's a great CodeProject article on working with exceptions to get you going.
But more to your point in the OP, Exceptions should only be handled where they need to be handled. This means that a well-implemented application will have a few points in the app (depending on scope of course) where a number of specific, Exception-derived exceptions will be handled and even fewer places (one per thread per a number of best practice suggesttions) where the generic Exception will be handled.
When working with exceptions, don't think in terms of a function returning error information. Exceptions greatly alleviate the tedium of percolating an error condition through your call chain.
No, you should not wrap all of your code in a try-catch. I answered a similar question here on dba.stackexchange.com - how much overhead an error in RDBMS has.
Generally you should only use exception handling if there's something specific that you want to do with the error message, or if the code that failed produces results that aren't used anywhere else. If the application is user-facing, you obviously don't want them seeing raw exception messages either. In all these cases, you should be logging the failure...no sense in trapping for an exception that you don't plan on handling (empty catch = bad). But otherwise, you will want an exception to be thrown.
For instance, you make a database call and it fails with a SQL Exception. The next part of your code is designed to process that result, so you will want an exception to be thrown and program execution to be halted.
If your code is regularly producing exceptions (and driving logic off of that), you should probably rethink your approach.
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Closed 13 years ago.
Possible Duplicate:
Do try/catch blocks hurt performance when exceptions are not thrown?
Hey everyone,
Just a quick question about try..catch blocks. I've heard they're expensive to use and shouldn't be used as part of a program's flow. However, in order to validate email addresses, I'm using the following code.
try
{
MailAddress checkEmail = new MailAddress(testEmail);
return true;
}
catch
{
return false;
}
Due to prior validation, I don't many exceptions to be caught unless it's an attempt to bypass validation. My question is, are Try...Catch blocks only expensive if an exception is caught, or is it always expensive regardless of whether any exception is thrown?
Thanks
EDIT : Thanks for all the replies. I've decided that since the checking (in C#) isn't very expensive, I'll stick with this method. It's mainly because an actual exception being thrown is rare since there are prior validation steps that ensure no one accidentally enters an invalid email address.
In general, in today's implementations, entering a try block is not expensive at all (this was not always true). However, throwing and handling an exception is usually a relatively expensive operation. So, exceptions should normally be used for exceptional events, not normal flow control.
Performance is only one factor to consider, though, especially in the modern world. If (for instance) you're doing something once in response to a user action, it probably doesn't matter from a performance standpoint whether you use an exception even when you could have done a proactive check instead, provided the exception happens quickly enough the user isn't jolted.¹ But if you're doing something in a tight loop that's going to run hundreds of thousands of times, or you're writing a web application that may need to handle a huge load, you'd probably want to avoid using an exception for a normal case.
¹ More than a decade ago I was responsible for enhancements to a .Net 1.1 "no touch deployment" application in which the first exception thrown took fully three seconds. This was a sufficient problem in one use case involving opening a file the user had asked for which might reasonably not be there that I had to add a check for file existence prior to trying to open the file, which is normally poor programming practice (just try to open the file and handle the exception if that fails), purely because the user experience waiting for that exception to get built was so poor. But that's probably not the world we live in now.
They are pretty cheap unless there is an exception. So you should avoid them when an exception is expected, as in your example above.
I think exceptions on bad user input are generally unwise. Exceptions on out of memory or other unexpected failures are fine.
Just to play devils advocate - I have found a great use for using Exceptions for flow control: The 'cancel' button.
If you have a function running on some service that may take 10-120 minutes, which is doing a bunch of different things, I've found that doing if(hasCanceled) throw new JobCancelledException() inside of my Log() function (which logs at each step that I'm at) to work just friggan awesome. It bails out of the current execution of code and stops running the job - exactly what I need. I'm sure there's some better way to do it, maybe somehow using events - but for my case it works great (especially since jobs are not regularly cancelled).
Other then that though - I'm 100% in agreement that Exceptions should never be used as a flow control tool..
#Kornel - I have two words for that post... Holy $hit =)
here's a simple pseudo code sample:
Class Job
{
Public Run(param1,param2,etc...)
{
Try
{
Log("Doing Something")
DoSomething()
Log("Doing Another")
DoAnother()
Log("This keeps going, etc, inside of these function we make the same Log calls where it makes sense")
Etc()
}
Catch(JobCancelledException)
{
status="Cancelled"
}
}
Private Log(ByVal str As String)
{
MessateToUser(str)
if(hasCancelled)
throw new JobCancelledException
}
private SomeEvent_WhenUserPushesCancelButton()
{
hasCancelled=True
}
}
Exceptions are only expensive if an exception is thrown. I'm sure there is some very minimal cost to setting up up a Try..Catch block but it is by far outweighed by the cost of not catching the exception at all and having your program crash. As others have pointed out, Try..Catch blocks should only be used for exceptional circumstances.
The overhead of the try block is very low, so if no exception is thrown then there should be no noticeable penalty. The main overhead that occurs when an exception is thrown is the stack walk that takes place looking for a handler - since you are caching the exception so close to the source, I doubt there will be much of a performance issue. Ideally though you would be able to validate your inputs properly beforehand, but email validation is fairly complicated so it may well not be worth it in this case.
It's only expensive if the exception is thrown, but that's not an excuse to use exceptions as normal flow control.
If you can pre-validate something to avoid an exception occurring in the first place, then do so. E.g. instead of what you posted, something like this would be preferable:
string invalidAddress = "notvalid######lolzors.bomb";
return MailAddressValidator.IsValid(invalidAddress ); // doesn't cause exception
The exception to the rule is when you'd have to roll your own version of a complicated method (e.g. something found in the base class library that doesn't have a TryParse method) just to avoid an exception that, in the grand scheme of things, just doesn't matter.
If you are unsure, profile using representative data. If it's a user entering data in a client app form every other second, it won't matter. However, if it's a service for processing batches of thousands of email addresses that could come from anywhere, you ought to be sure of your assumptions.
try..catch blocks should never be used as a tool for program flow control.
Read this thread if you're unconvinced.
In general, modern compilers impose only a minimal cost on try blocks unless an exception is thrown. They still shouldn't be used for program flow control, as they aren't as obvious as standard flow constructs. An exception is essentially equivalent to a COME FROM statement.
While it is true that you should never use try..catch for program flow control, I am not aware of any performance issues IF no exceptions are actually thrown in the code
This is language-dependent, but as far as I know in Java, if no exception is thrown, there is next to no performance cost to having a try/catch.
So in your example of using pre-validated email addresses, what you have is fine.
I'd like a response from someone who actually does real-time programming in C# or who really understands the language internals.
I know that exceptions should not be used to handle normal processing, but only to detect error conditions. There is plenty of discussion on that topic.
I'd like to know if there is any run time slow-down from simply having a try/catch block in place (which never catches an exception unless the program will have to end anyway). The try/catch block is inside a function which must be called repeatedly. I suspect there is only minimal cost.
Can the cost be quantified in terms of CPU cycles, or other tasks (same cost as a floating point multiplication), or another way?
We use Microsoft C#.Net 3.5 under windows XP.
.NET exceptions have a very, very low overhead cost unless they are thrown. Having a try/catch block in place will have a very minimal performance impact. I have found nearly no impact, even in very fast, tight loops, to having exception handling in place.
However, exceptions in .NET are VERY expensive when they're thrown. They tend to be much high-impact on performance if you throw them than many other languages. This is due to the full stack information gleaned when the exception is created, etc.
This is the opposite behavior to some other languages, such as python, where exception handling has a higher cost, but throwing is actually fairly performant.
However, if you are concerned, I would suggest you profile your routine, and test it yourself. This has been my experience after quite a bit of performance profiling. There is no substitution for measuring in your own codebase.
Good discussion, with metrics, of performance implications of try catch here.
Do try/catch blocks hurt performance when exceptions are not thrown?