Stephen Robert Norris wrote: > > I'd be interested to know how to avoid that. I'm pretty sure I can > construct a scenario (with multiple threads and memory mapping, > for example) where it's impossible to tell until you get the SEGV. For > instance, I memory map a file, pass a pointer into the mapped > region into the library and then unmap it some time later from another > thread. > > Even if the library were checking (and I'm not sure how it could) that > the pointer points to valid address space, there will be a time gap > between the check and the use, and my unmapping can get in there. > > Having the library install its' own signal handler is not an acceptable > solution, either. Well, call me stupid, but isn't that what mutexes are for? Thread 1 sets the mutex, then calls the library with a pointer to some part of the shared memory. Make sure thread 2 checks the mutex before unmapping and there's no problem at all. Thing is, how is the library going to know whether the pointer is valid or not? All the standard C functions that expect pointers will happily write wherever you point them to, even if it causes a segfault. I don't see how this is a problem with the library. If I divide by zero (which is essentially calling the divide function with illegal values) I get an exception as well. Lourens
