Re: Memory leak in select

[Peter Rosin <peda@lysator.liu.se>]

Den 2011-04-18 14:23 skrev Peter Rosin:
> Den 2011-04-18 13:43 skrev Peter Rosin:
>> Hi!
>>
>> Using the following STC, I'm seeing what appears to be a memory
>> leak in select(2).
>>
> ----------------8<---(selectleak.c)---------
> #include <sys/time.h>
> #include <fcntl.h>
> 
> int
> main(void)
> {
> 	fd_set fdset;
> 
> 	long flags = fcntl(0, F_GETFL);
> 	fcntl(0, F_SETFL, flags | O_NONBLOCK);
> 
> 	for (;;) {
> 		int res;
> 		char buf[20];
> 
> 		FD_ZERO(&fdset);
> 		FD_SET(0, &fdset);
> 		res = select(1, &fdset, NULL, NULL, NULL);
> 		if (!res)
> 			continue;
> 		if (res < 0)
> 			return 1;
> 		res = read(0, buf, sizeof(buf));
> 		if (!res)
> 			break;
> 		if (res < 0)
> 			return 1;
> 	}
> 
> 	return 0;
> }
> ----------------8<--------------------------

Ok, I'm taking a wild swing at this, and my guess is that the call
sel.cleanup () in cygwin_select prematurely zeros out the cleanup
member of the select_record. The call to sel.poll () then adds
"stuff" to the select_record that really should have been cleaned
up, but isn't since cleanup has already been executed and then
zapped (by select_stuff::cleanup).

But what do I know?

Cheers,
Peter

extern "C" int
cygwin_select (int maxfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds,
               struct timeval *to)
{
  select_stuff sel;
  fd_set *dummy_readfds = allocfd_set (maxfds);
  fd_set *dummy_writefds = allocfd_set (maxfds);
  fd_set *dummy_exceptfds = allocfd_set (maxfds);

  ...

  sel.cleanup ();                          // Too early ???
  copyfd_set (readfds, r, maxfds);
  copyfd_set (writefds, w, maxfds);
  copyfd_set (exceptfds, e, maxfds);
  return timeout ? 0 : sel.poll (readfds, writefds, exceptfds);
}

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