Keean Schupke wrote:
"C exit routines" aren't responsible for freeing OS resources; the OS is.
The fact that the SysV IPC objects aren't freed on exit is intentional; they are meant to be persistent. For the same reason, the OS doesn't delete upon termination any files which the process created.
Right, which is why if you want to clean up temporary files, or temporary semaphores the OS doesn't do it for you, and you need to put some routine inplace to do it (using at_exit)... It seems this is the only way to guarantee something gets run when a program exits for whatever reason.
There isn't any way to *guarantee* that something is run upon
termination. The program may be terminated due to SIGKILL (e.g. due to
a system-wide lack of virtual memory). If you run out of stack, you
may not be able to call functions to perform clean-up.
Also, if the program crashes, handling the resulting SIGSEGV (etc) is
likely to be unreliable, as the memory containing the resource
references may have been trashed. Calling remove() on a filename which
might have been corrupted is inadvisable.
Also, at_exit() isn't standard. atexit() is ANSI C, but that is only
supposed to be called for normal termination (exit() or return from
main()), not for _exit() or fatal signals.
--
Glynn Clements