Bugtraq mailing list archives
Re: pingflood.c
From: jhutz+ () cmu edu (Jeffrey Hutzelman)
Date: Mon, 18 May 1998 15:51:27 -0400
The reason that this works is because many platforms implement sleep(2) as: alarm(seconds); sigsuspend(...); This is implementation is done in Solaris, etc. I have implemented my own sleep function because when using threads under Solaris, messing with signals is a bad proposition. So:
Ummm... I don't know what version of Solaris you're using, but as of 2.5, sleep(3c) is MT-Safe. So long as you're not playing with SIGALRM yourself, it works as expected in multi-threaded as well as single-threaded applications.
void mysleep(int seconds) { struct timeval tv; tv.tv_sec=seconds; tv.tv_usec=0; select(0,NULL,NULL,NULL,&tv); } The code above should be portable to every platform that supports the standard select(2) semantics. It allows for subsecond precision too. This implementation isn't subject to signal dainbrammage either.
This, on the other hand, has the problem that the sleep can terminate prematurely if any signal is delivered - select(3c) will exit with EINTR in that case. Unfortunately, select is not guaranteed to tell you how much time is remaining, so you must keep track of when to wake up and keep sleeping until that time arrives. Note that neither sleep(3c) nor select(3c) is a system call on Solaris. As you pointed out, sleep() is implemented in terms of alarm(2) and SIGALRM, on Solaris and most other platforms as well. On many SysV-ish platforms, including Solaris, select() is implemented in terms of poll(), which has only millisecond accuracy. Overall, the best approach for programs like ping would be to use select, with a loop to trap interruptions: void safe_sleep(int seconds) { time_t when, now; struct timeval tv; when = time(0) + seconds; for (;;) { now = time(0); if (now >= when) return; tv.tv_sec = when - now; tv.tv_usec = 0; if (select(0, 0, 0, 0, &tv) >= 0 || errno != EINTR) return; } } -- Jeffrey T. Hutzelman (N3NHS) <jhutz+ () cmu edu> Systems Programmer School of Computer Science - Research Computing Facility Carnegie Mellon University - Pittsburgh, PA
Current thread:
- Re: pingflood.c Aggelos P. Varvitsiotis (May 18)
- Re: pingflood.c pedward () WEBCOM COM (May 18)
- Re: pingflood.c Jeffrey Hutzelman (May 18)
- Re: pingflood.c Phil Stracchino (May 18)
- root from file table overflows? Chris Conner (May 19)
- Re: pingflood.c Theo de Raadt (May 18)
- Re: pingflood.c sinster () DARKWATER COM (May 18)
- <Possible follow-ups>
- Re: pingflood.c pedward () WEBCOM COM (May 18)
- Re: pingflood.c Niall Smart (May 18)
- Re: pingflood.c pedward () WEBCOM COM (May 18)