Thursday, September 24, 2009

PHP, reliability, ASP and remote desktops

I've been working in ASP on an IIS server recently. Not my environment of choice, but the scripts I need to write are relatively simple, so I decided it was easier to go with it than ask for PHP to be installed (which then requires apache). This is quite a helpful page:

We'll see how it goes. In many of the systems I work on, windows or linux, I usually use commandline PHP as the glue. I'm always amazed at how rock solid it is. Especially on Windows it is always the most stable element. E.g. I've a 24/7 PHP script that deals with COM objects. The COM objects crash regularly. But I just catch the exception in PHP, delete the COM object, create another one and off we go. Needing to use 3rd party libraries only available in C are the only reason I write C++ recently, but they cause me no end of trouble (mysterious crashes deep in windows system calls for instance). Windows itself needs to be rebooted every 3 or 4 weeks or it starts to go all wobbly on us, and my 24/7 PHP scripts simply run for those 4 weeks without a single problem or restart.

Of course saying PHP is more stable than C would be stupid; PHP is itself a C app. The difference is that PHP is a well-crafted piece of code, better than the COM objects, 3rd party C libraries and Microsoft OSes I'm comparing it to.

Going back to IIS, I don't have it installed locally, so have been developing on a remote server. "rdesktop" wins this month's "application I wish I'd discovered months ago" award. Previously I would have to boot up my windows notebook just to use remote desktop. rdesktop gives me this functionality on linux, works perfectly (touch wood) and copy and paste works too.

Thursday, September 3, 2009

Windows SEH in C++

A windows app was mysteriously dying, roughly once a day; no clues in any of the various log files.
So I enabled Windows SEH:

(See MSDN article about _set_se_translator)

And here is my implementation of that function:

void win32_exception_handler(unsigned int code, EXCEPTION_POINTERS *ep){
throw new win32_exception(code,ep);

And the class (cut down to basics) is:

class win32_exception{
std::string info;
win32_exception(unsigned int code,EXCEPTION_POINTERS *ep){
//Describe it in info
const char *what()const{return info.c_str();}

Then, I have this code (which was already here before I enabled SEH):

catch(std::exception &e){
ErrorLog()<<"Got a std::exception thrown by main_loop:"<<e.what()<<" (will treat as fatal)\n";
return -9;
catch(win32_exception &e){
ErrorLog()<<"Caught win32_exception thrown by main_loop:"<<e.what()<<" (will treat as fatal)\n";
return -9;
ErrorLog()<<"Got an unexpected exception thrown by main_loop (will treat as fatal)\n";
return -9;

Now, what I don't get is today the program died with this message:
Got an unexpected exception thrown by main_loop (will treat as fatal)

I'm staring and staring at the code and don't get why the win32_exception code didn't catch and instead some other exception type got caught. Enabling SEH was the only change, all such exceptions should go through my function, and that only throws win32_exception instances.

The other mystery to me is what is the type is of this "unexpected" exception.

(I'm hoping to come back and add to this blog entry when I work out what is going on!)