Date: Fri, 13 Jul 2012 23:05:47 +0200 From: Jilles Tjoelker <jilles@stack.nl> To: David Xu <davidxu@freebsd.org> Cc: freebsd-threads@FreeBSD.org Subject: Re: threads/168417: pthread_getcpuclockid() does not work to specification Message-ID: <20120713210547.GA67646@stack.nl> In-Reply-To: <201207120800.q6C80ISC073892@freefall.freebsd.org> References: <201207120800.q6C80ISC073892@freefall.freebsd.org>
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On Thu, Jul 12, 2012 at 08:00:18AM +0000, David Xu wrote: > The following reply was made to PR threads/168417; it has been noted > by GNATS. > From: David Xu <davidxu@freebsd.org> > To: bug-followup@freebsd.org, chris.hall@highwayman.com > Cc: > Subject: Re: threads/168417: pthread_getcpuclockid() does not work to specification > Date: Thu, 12 Jul 2012 15:51:02 +0800 > I have worked out a patch trying to fix the problem: > http://people.freebsd.org/~davidxu/patch/cputime_clockid.diff Some comments: * Should clock_getcpuclockid() and clock_getthreadcpuclockid() be syscalls or can the 2**31 reserved clock ids be hard-coded into libc just like the other clock ids are? * Perhaps clock_getcpuclockid() should check if the pid is valid. * I think p_canwait() is not the right permission check. The p_canwait() check is for wait4() and takes into account that denying at that point completely breaks the process's tracking of its child processes. The right permission check is probably p_cansee() because that's what the kern.proc.* sysctls that return CPU time also check. The recently added pget() function can perform pfind() and p_cansee() in one call. * Why can a thread's CPU clock only be read from the same process? The kern.proc.* sysctls allow querying any thread whose process you p_cansee. However, the POSIX APIs only allow accessing threads within the process because there is no pthread_t for other threads. -- Jilles Tjoelker
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