Thread: my method to optimize application startup performance

Hello everyone,


I found that for an application, if I specify the entry point function (e.g. main), the performance of startup will be greatly improved.

My questions are,

1. If no entry point is specified, how will debugger of Visual Studio find the entry point function? Will the time to search entry point function long?

For example, in my application, I defined the main function like this,

int main(void)

how will debugger treat main as the start point to execute (I set a break point to this function if I do not specify the entry point, then after a couple of minutes after pressing F5 to trigger debugger, debugger will jumps to main)?

If I specify the entry point to main, then debugger will directly jumps to this function after F5 debugging.

2. Specify entry point is a way to improve performance?


thanks in advance,
George

Originally Posted by matsp

Huh? Can you explain what you mean? "main" is ALWAYS the entry point, but perhaps what you actually mean is that you tell the debugger to set a breakpoint at main, rather than run in debug mode all the way through the startup code, or some such?

--
Mats

main() is *never* the entry point of a program. Before main is executed, a number of functions are called, such as functions that set up the stack, heap and so on, and also constructor functions, if you specified any.

Originally Posted by IceDane

main() is *never* the entry point of a program. Before main is executed, a number of functions are called, such as functions that set up the stack, heap and so on, and also constructor functions, if you specified any.

OK, but main() is the default entry point as far as functions that you actually write. I've never seen a way (other than using assembly or compiler switches) to define those other things that get setup before main().

Originally Posted by laserlight

Perhaps we could avoid being pedantic and just say "the function called at program startup" instead of "the entry point function", since the former seems to be what George2 is referring to.

I dislike the word "pedantic" - I prefer "detailed."

Anyway, if you're not detailed, you can risk misinforming people. The function called at program start up could be a constructor, if you define a function in your program with the constructor attribute, and besides that, there are many functions called before main which are put in there by your compiler.

I'd call it, "the function which stores your code," really, as that's pretty much what it is. Main is never the first or last function to be called.

Let's put it as the entry-point to your CODE and NOT your program, then?

Originally Posted by laserlight

Section 5.1.2 of C99 disagrees with respect to "function called at program start up", at least for a hosted environment:


"Entry point" seems a little more ambiguous, but clearly if "all objects with static storage duration shall be initialized before program startup", program startup is not the entry point. That said, call it "pedantic" or "detailed" if you like, but all this context depends on what George2 is really asking, and I think he needs to clarify that.

I agree that he needs to clarify, yes, but even so, what you quoted is ambiguous, too.

"Program startup" doesn't necessarily mean "start of the executable code" - Just try loading an application compiled with your favorite compiler in a debugger and you'll see.

So, you want to skip all that "useless" initialization of the environment and standard library and go straight to main(). Okay chief. Yeah. You're optimizing now.

Originally Posted by brewbuck

So, you want to skip all that "useless" initialization of the environment and standard library and go straight to main(). Okay chief. Yeah. You're optimizing now.

wonderful :-D

I'd be more concerned about performance after startup, since most programs spend a lot more time running than they do starting.

Originally Posted by cpjust

I'd be more concerned about performance after startup, since most programs spend a lot more time running than they do starting.

Originally Posted by sloppy

wonderful :-D

As cpjust said, your optimization will be pointless. I'm pretty sure that most (good) compilers optimize as much as they can without sacrificing anything necessary.