Date: Sun, 18 May 1997 21:14:26 +0800 From: Peter Wemm <peter@spinner.DIALix.COM> To: =?KOI8-R?B?4c7E0sXKIP7F0s7P1w==?= <ache@nagual.pp.ru> Cc: Bruce Evans <bde@zeta.org.au>, peter@FreeBSD.ORG, cvs-all@FreeBSD.ORG, cvs-committers@FreeBSD.ORG, cvs-lib@FreeBSD.ORG Subject: Re: cvs commit: src/lib/libc/gen sleep.c Message-ID: <199705181314.VAA07838@spinner.DIALix.COM> In-Reply-To: Your message of "Sun, 18 May 1997 15:07:12 %2B0400." <Pine.BSF.3.96.970518150412.1533B-100000@nagual.pp.ru>
next in thread | previous in thread | raw e-mail | index | archive | help
=?KOI8-R?B?4c7E0sXKIP7F0s7P1w==?= wrote: > On Sun, 18 May 1997, Peter Wemm wrote: > > > (void) sigvec(SIGALRM, &vec, &ovec); > > if (setjmp(&jmpbuf) == 0) { > > .. unmask SIGALRM .. > > I think here is a race place --> No, because if a SIGALRM is taken before getting into nanosleep(), the signal handler longjmp's out, and the nanosleep() isn't called. So, if we recieve a sigalarm inside sleep(3), we don't sleep (as intended). However, there are so many races here already it's not funny.. like, what happens if we get a signal before masking SIGALRM in the first place? > > nanosleep(&time_to_sleep, &time_remaining); > > (void) sigvec(SIGALRM, &ovec, (struct sigvec *)0); > > > ... but this has several problems.. > > 1: it's starting to get messy with lots of syscalls. > > 2: it doesn't deal with an aborted nanosleep() due to SIGALRM. It'd have > > to calculate the elapsed time itself by calling gettimeofday or > > clock_gettime() before and after. It'd also suffer from time adjustments > > and contribute to the mess. > > Yes. Hmm.. or we could initialise time_remaining to the full value. If nanosleep() never gets called, we can simply return the full value since we never really slept. > > On the other hand, perhaps we could change the nanosleep syscall so that > > it takes a mask argument and handle the differences in the libc wrapper > > and have sleep(3) do this: > > > > > > sigprocmask(SIG_BLOCK, ..SIGALRM.., &oset); > > ... > > setsignal(SIGALRM, sleephandler); > > ... > > nanosleep_mask(&time, &remaining, &oset); > > ... > > > and have nanosleep(ts1, ts2) be implemented as nanosleep_mask(ts1, ts2, > > NULL); > > The second variant looks much better. Bleah.. signanosleep()? wait for an unmasked signal (mask specified in syscall) for up to the max time limit. > -- > Andrey A. Chernov > <ache@null.net> > http://www.nagual.pp.ru/~ache/ Cheers, -Peter
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199705181314.VAA07838>