잡다한 이야기

I’ve seen this question a few times on the newsgroup so I thought I’d take a stab at it. We’re having another freak winter storm in Redmond so it’s not like I can leave work anyway…

What is GWES?

Gwes is the Graphical Windowing and Event Subsystem. It’s one little program that draws all the controls on the device like scrollbars, buttons, and checkboxes. It also handles passing window messages back and forth between applications and manages the WndProcs of all of the programs on the device that are displaying UI.

So why does it crash all the time?

A crash dump (“Watson dump”) is usually triggered by an unhandled exception in a program. It packages up a callstack and some diagnostics and queues it for transmission up to our Windows Error Reporting database.

If a program (let’s call it test.exe) crashes inside WinMain, the exception gets out to the unhandled exception trap in the kernel which creates the Watson dump and then terminates test.exe.

But what if test.exe crashes inside its WndProc? The exception travels up the callstack. The next process up the callstack is GWES – GWES is the process that calls each WndProc in the first place, because it’s marshalling the window messages throughout the system.

What if GWES didn’t handle exceptions that were thrown from your WndProc? Then any crashing WndProc would crash GWES without fail and take down the entire system. That doesn’t happen, so we know that’s not true. GWES handles exceptions thrown out of other WndProcs. So GWES is responsible for triggering a Watson dump when another program crashes in a WndProc.

The problem is that when the Watson dump is created, it sees that GWES is at the top of the callstack, so GWES gets the place of honor in the Watson UI that you see in the screenshot above. We have fixed this for future versions of the system [edit: including WM6] - crashes inside a WndProc will show the correct process name in the "We're Sorry..." UI.

Sometimes it really is just sorry.

That said, it is possible that GWES really is crashing for some reason. So please keep sending those error reports up to us. We use them to diagnose problems and prioritize fixes towards the crashes that customers are hitting the most often.

출처: http://blogs.msdn.com/b/windowsmobile/archive/2007/01/10/who-is-gwes-and-why-does-it-keep-apologizing.aspx

1. 기본형

#include <stdio.h>

int add(int a, int b){ return a+b; }
int sub(int a, int b){ return a-b; }
int mul(int a, int b){ return a*b; }

int (*pa[3])() = {add, sub, mul};

int compute(int op, int a, int b)
{
     return pa[op](a, b);
}

void main(void)
{
     printf("%d\n", compute(0,3,4));
     printf("%d\n", compute(1,3,4));
     printf("%d\n", compute(2,3,4));
}

2. 확장형

#include <stdio.h>

int add(int a, int b){ return a+b; }
int sub(int a, int b){ return a-b; }
int mul(int a, int b){ return a*b; }
int sqr(int a){ return a*a; }

int (*pa[4])( ) = {add, sub, mul, sqr};

int (*compute(int op))()
{
     return pa[op];
}

void main(void)
{
     printf("%d\n", compute(0)(3,4));
     printf("%d\n", compute(1)(3,4));
     printf("%d\n", compute(2)(3,4));
     printf("%d\n", compute(3)(3));
}