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Re: Catching signal errors
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Re: Catching signal errors



Matt Watson wrote:

void fatalSigHandler(int sig, siginfo_t* info, void* context)
{
// We are very limited in what we are allowed to do in a signal handler. // Memory should not be allocated, and most libc functions should not be used.
static char sig_message[] = "Aborting: Fatal signal occurred!\n";


   write(1, sig_message, sizeof(sig_message));
   exit(1);
}


Never call exit() from a signal handler. You want _Exit() instead. exit() will call atexit() handlers which will are likely not signal-safe. And you probably want to use fd 2 (stderr), instead of fd 1 in the write() call.


Good suggestions. That's especially important when using dlopen or NSLinkModule on libraries. They could cause further signals or even signal deadlocks when they get unloaded.


That said: if you're not going to add any more info in your signal handler, or do any cleanup like unlink() files, it may just be best to let it crash and generate a crash log.


I assumed that he'd replace the handler with something else.
One of the handlers I have for a project calls execv() to restart the daemon in case of a crash. That is after writing errors to a log and closing open file handles/resetting signal masks (as they are both inherited by the new process), and doing some other general cleanup of the daemon's lock/state files.


-Kevin-

Thanks everyone!!!!

I hope no one minds if I take this one step further. Is there actually a way to have it return to the offending code with an exception triggered? For example, would the following snippet work...

#define	kMySigError	-9999

void fatalSigHandler(int sig, siginfo_t* info, void* context)
{
    short  pErr = kMySigError;
    throw(pErr);
    _Exit(1);		//Not that this will ever be reached
}

main(){
	Ptr	ptrFoo = nil;
	char	barrrr;
   installSignalHandler(SIGSEGV, &fatalSigHandler);
   installSignalHandler(SIGBUS, &fatalSigHandler);

try{
	barrrr = (*ptrFoo);
}catch(short err){
	printf("Error %x", err);
}
	....continue
	return(noErr);
}

Rick
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References: 
 >Catching signal errors (From: Rick Steele <email@hidden>)
 >Re: Catching signal errors (From: Kevin Harris <email@hidden>)
 >Re: Catching signal errors (From: Matt Watson <email@hidden>)
 >Re: Catching signal errors (From: Kevin Harris <email@hidden>)



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