Regular Expression to Get the Src of Images in C#

Do try/catch blocks hurt performance when exceptions are not thrown?

Check it.

static public void Main(string[] args)
{
    Stopwatch w = new Stopwatch();
    double d = 0;

    w.Start();

    for (int i = 0; i < 10000000; i++)
    {
        try
        {
            d = Math.Sin(1);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }

    w.Stop();
    Console.WriteLine(w.Elapsed);
    w.Reset();
    w.Start();

    for (int i = 0; i < 10000000; i++)
    {
        d = Math.Sin(1);
    }

    w.Stop();
    Console.WriteLine(w.Elapsed);
}

Output:

00:00:00.4269033  // with try/catch
00:00:00.4260383  // without.

In milliseconds:

449
416

New code:

for (int j = 0; j < 10; j++)
{
    Stopwatch w = new Stopwatch();
    double d = 0;
    w.Start();

    for (int i = 0; i < 10000000; i++)
    {
        try
        {
            d = Math.Sin(d);
        }

        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }

        finally
        {
            d = Math.Sin(d);
        }
    }

    w.Stop();
    Console.Write("   try/catch/finally: ");
    Console.WriteLine(w.ElapsedMilliseconds);
    w.Reset();
    d = 0;
    w.Start();

    for (int i = 0; i < 10000000; i++)
    {
        d = Math.Sin(d);
        d = Math.Sin(d);
    }

    w.Stop();
    Console.Write("No try/catch/finally: ");
    Console.WriteLine(w.ElapsedMilliseconds);
    Console.WriteLine();
}

New results:

   try/catch/finally: 382
No try/catch/finally: 332

   try/catch/finally: 375
No try/catch/finally: 332

   try/catch/finally: 376
No try/catch/finally: 333

   try/catch/finally: 375
No try/catch/finally: 330

   try/catch/finally: 373
No try/catch/finally: 329

   try/catch/finally: 373
No try/catch/finally: 330

   try/catch/finally: 373
No try/catch/finally: 352

   try/catch/finally: 374
No try/catch/finally: 331

   try/catch/finally: 380
No try/catch/finally: 329

   try/catch/finally: 374
No try/catch/finally: 334

try catch for performance c#

The link I provided in the above comment shows a description of why you shouldn't ever use a try-catch when an if-statement would prevent the exception from being thrown, but in the interest of showing performance in terms of actual numbers, I wrote this quick little test program.

Stopwatch watch = new Stopwatch();

int[] testArray = new int[] { 1, 2, 3, 4, 5 };
int? test = null;

watch.Start();
for (int i = 0; i < 10000; i++)
{
    try
    {
        testArray[(int)test] = 0;
    }
    catch { }
}
watch.Stop();

Console.WriteLine("try-catch result:");
Console.WriteLine(watch.Elapsed);
Console.WriteLine();

watch.Restart();
for (int i = 0; i < 10000; i++)
{
    if (test != null)
        testArray[(int)test] = 0;
}
watch.Stop();

Console.WriteLine("if-statement result:");
Console.WriteLine(watch.Elapsed);

The result of the program is this:

try-catch result:
00:00:32.6764911

if-statement result:
00:00:00.0001047

As you can see, the try-catch approach introduces significant overhead when an exception gets caught, taking over 30 seconds to complete 10,000 cycles on my machine. The if-statement, on the other hand, runs so fast that it is basically instantaneous. Compared to the try-catch, this is a performance improvement in the neighborhood of 3,000,000%.

(This isn't a rigorous benchmark, and there are ways to write it and run it differently to get more precise numbers, but this should give you a good idea of just how much more efficient it is to use an if-statement over a try-catch whenever possible.)

try catch performance

The JIT doesn't perform optimization on 'protected' / 'try' blocks and I guess depending on the code you write in try/catch blocks, this will affect your performance.

does try catch clause affect performance?

Neither try/catch nor try/catch/finally affects performance to any significant degree. Exceptions being created do affect performance, of course (and that is whether they are caught, or not)

Do try/catch blocks hurt performance when exceptions are not thrown?

Try-Catch vs If performance in C#

Exceptions are not made to control the flow of your code. They are made to treat "exceptional" circumstances, e.g. connection issues or invalid file formats.

If you want to control your code flow, you should use conditional statements like if, else and switch.

The performance of exceptions is generally bad compared to some simple if-statement, but there are also situations when exception-handling might be even faster than checking data for validity manually, especially if you don't know how to do it fast.
There might also be plenty of situations where you "know" an exception could be raised, but you simply trust the data - e.g. checking your own settings file for valid xml format.

Most of the time, you want to use Exceptions, to have error information later, e.g. line number of the error in the xml file and to recover your application in some way (e.g. reconnect to a socket).

You can not give a general statement about the performance of exceptions, but when you can avoid them, you should.
They are made for exceptions as their name already tells.

A small example where you can potentially avoid exceptions:

try
{
    LoginUser("Fooooo", "Bar");
} catch(InvalidPasswordException e) {
    MessageBox.Show(e.Message);
}  

private static void LoginUser(string pUsername, string pPassword)
{
    if (pUsername != "Foo" || pPassword != "Bar")
       throw new InvalidPasswordException("Invalid username and/or password");
    
    GrantAccess(pUsername);
}

Instead of throwing the exception you could also just return a boolean:

if (!LoginUser("Fooooo", "Bar"))
{
    MessageBox.Show("Invalid username and/or password");
}

private static bool LoginUser(string pUsername, string pPassword)
{
    if (pUsername != "Foo" || pPassword != "Bar")
        return false;
        
    GrantAccess(pUsername);            
    return true;
} 

Performance-Test: 10000 attempts with false credentials:

throwing Exception (without displaying the messagebox): 181990454 ticks

returning boolean: 644 ticks

And we are only 1 layer into the application, so there is not much stacktrace to be generated. I guess you can see and especially feel the difference.

In Javascript, is it expensive to use try-catch blocks even if an exception is never thrown?

Are you doing typical CRUD UI code? Use try catches, use loops that go to 10000 for no reason sprinkled in your code, hell, use angular/ember - you will not notice any performance issue.

If you are doing low level library, physics simulations, games, server-side etc then the never throwing try-catch block wouldn't normally matter at all but the problem is that V8 didn't support it in their optimizing compiler until version 6 of the engine, so the entire containing function that syntactically contains a try catch will not be optimized. You can easily work around this though, by creating a helper function like tryCatch:

function tryCatch(fun) {
    try {
        return fun();
    }
    catch(e) {
        tryCatch.errorObj.e = e;
        return tryCatch.errorObj;
    }
}
tryCatch.errorObj = {e: null};

var result = tryCatch(someFunctionThatCouldThrow);
if(result === tryCatch.errorObj) {
    //The function threw
    var e = result.e;
}
else {
    //result is the returned value
}

After V8 version 6 (shipped with Node 8.3 and latest Chrome), the performance of code inside try-catch is the same as that of normal code.

Java try/catch performance, is it recommended to keep what is inside the try clause to a minimum?

In your example here, the real performance hit is if both doSomething() and doAnotherThing() both throw exceptions. Entering a try-block is fast, until it throws an exception.

It really comes down to what your situation is. If you need to do the same thing when MyCheckedException is thrown either way, I'd consider it both more readable and more performant to have them both in the same try block, but if you need to handle the two different situations differently then of course it makes more sense to separate them.

Edit: I read the end of your comment, you're assuming handling both the same way, in which case I'd put them both in the same try-block.

Does try-catch block decrease performance

TL;DR NO, exceptions are usually faster on the non-exceptional path compared to error code handling.

---

Well, the obvious remark is compared to what ?

Compared to not handling the error, it obviously decrease performance; but is performance worth the lack of correctness ? I would argue it is not, so let us supposed that you meant compared to an error code checked with an if statement.

In this case, it depends. There are multiple mechanisms used to implement exceptions. Actually, they can be implemented with a mechanism so close to an if statement that they end up having the same cost (or slightly higher).

In C++ though, all major compilers (gcc introduced it in 4.x serie, MSVC uses it for 64 bits code) now use the Zero-Cost Exception Model. If you read this technical paper that Need4Sleep linked to, it is listed as the table-driven approach. The idea is that for each point of the program that may throw you register in a side-table some bits and pieces that will allow you to find the right catch clause. Honestly, it is a tad more complicated implementation-wise than the older strategies, however the Zero Cost name is derived by the fact that it is free should no exception be thrown. Contrast this to a branch misprediction on a CPU. On the other hand, when an exception is thrown, then the penalty is huge because the table is stored in a cold zone (so likely requires a round-trip to RAM or worse)... but exceptions are exceptional, right ?

To sum up, with modern C++ compilers exceptions are faster than error codes, at the cost of larger binaries (due to the static tables).

---

For the sake of exhaustiveness, there is a 3rd alternative: abortion. Instead of propagating an error via either status or exception, it is possible to abort the process instead. This is only suitable in a restricted number of situations, however it optimizes better than either alternative.

Cost of exception handlers in Python

Why don't you measure it using the timeit module? That way you can see whether it's relevant to your application.

OK, so I've just tried the following (using Python 3.11.1 on Windows 11):

import timeit

statements=["""\
try:
    b = 10/a
except ZeroDivisionError:
    pass""",
"""\
if a:
    b = 10/a""",
"b = 10/a"]

for a in (1,0):
    for s in statements:
        t = timeit.Timer(stmt=s, setup='a={}'.format(a))
        print("a = {}\n{}".format(a,s))
        print("%.2f usec/pass\n" % (1000000 * t.timeit(number=100000)/100000))

Result:

a = 1
try:
    b = 10/a
except ZeroDivisionError:
    pass
0.06 usec/pass

a = 1
if a:
    b = 10/a
0.05 usec/pass

a = 1
b = 10/a
0.03 usec/pass

a = 0
try:
    b = 10/a
except ZeroDivisionError:
    pass
0.27 usec/pass

a = 0
if a:
    b = 10/a
0.02 usec/pass

a = 0
b = 10/a
Traceback (most recent call last):
  File "<stdin>", line 5, in <module>
  File "C:\Python311\Lib\timeit.py", line 178, in timeit
    timing = self.inner(it, self.timer)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<timeit-src>", line 6, in inner
ZeroDivisionError: division by zero

As you can see, there is not much of a difference between using a try/except clause vs. an explicit if statement, unless the exception gets triggered. (And of course, not having any control structure is fastest, though not by much, and it will crash the program if anything goes wrong).

Compare this to the results obtained in 2010:

a = 1
try:
    b = 10/a
except ZeroDivisionError:
    pass
0.25 usec/pass

a = 1
if a:
    b = 10/a
0.29 usec/pass

a = 1
b = 10/a
0.22 usec/pass

a = 0
try:
    b = 10/a
except ZeroDivisionError:
    pass
0.57 usec/pass

a = 0
if a:
    b = 10/a
0.04 usec/pass

a = 0
b = 10/a
ZeroDivisionError: int division or modulo by zero

I appears that the PC I'm using now is about twice as fast as the one I had back then. The cost of handling an Exception appears identical, and the "normal" operations (arithmetic) have been improved even more than the handling of control structures, but the point from all those years ago still stands:

It's all within the same order of magnitude and unlikely to matter either way. Only if the condition is actually met (often), then the if version is significantly faster.

---

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