svn commit: r231989 - in head: lib/libthr/thread sys/kern sys/sys

[Jilles Tjoelker]

On Thu, Feb 23, 2012 at 08:07:49AM +0800, David Xu wrote:
> On 2012/2/23 7:42, Jilles Tjoelker wrote:
> > On Wed, Feb 22, 2012 at 03:22:50AM +0000, David Xu wrote:
> >> Author: davidxu
> >> Date: Wed Feb 22 03:22:49 2012
> >> New Revision: 231989
> >> URL: http://svn.freebsd.org/changeset/base/231989
> >> Log:
> >>    Use unused fourth argument of umtx_op to pass flags to kernel for operation
> >>    UMTX_OP_WAIT. Upper 16bits is enough to hold a clock id, and lower
> >>    16bits is used to pass flags. The change saves a clock_gettime() syscall
> >>    from libthr.
> >> Modified:
> >>    head/lib/libthr/thread/thr_umtx.c
> >>    head/sys/kern/kern_umtx.c
> >>    head/sys/sys/umtx.h
> >>
> >> Modified: head/lib/libthr/thread/thr_umtx.c
> >> ==============================================================================
> >> --- head/lib/libthr/thread/thr_umtx.c	Wed Feb 22 01:50:13 2012	(r231988)
> >> +++ head/lib/libthr/thread/thr_umtx.c	Wed Feb 22 03:22:49 2012	(r231989)
> >> @@ -200,20 +200,10 @@ int
> >> +	       	abstime != NULL ? (void *)(uintptr_t)((clockid<<  16) | UMTX_WAIT_ABSTIME) : 0,
> > Please check that this shift does not lose any information (i.e.,
> > clockid>= 0&&  clockid<= 0xFFFF) before doing it.

> > Implementing clock_getcpuclockid() will require clockids greater than
> > 65535 because such clockids contain a process id.

> In which document said the clock id includes a process id ? I think the 
> clock_getcpuclockid()
> is a simplified version of getrusage().

clock_getcpuclockid() lets you find a clock ID for the CPU time clock of
a process. Usage could be like this:

int error;
pid_t pid;
clockid_t clk;
struct timespec ts;

error = clock_getcpuclockid(pid, &clk);
if (error == 0)
	if (clock_gettime(clk, &ts) == 0)
		printf("%lu.%09lu\n", (unsigned long)ts.tv_sec,
		    (unsigned long)ts.tv_usec);

One way to implement it is to reserve a PID_MAX sized subrange of
clockid_t for this purpose.

Similarly, pthread_getcpuclockid() lets you find a clock ID for the CPU
time clock of a thread.

These seem mostly useful for clock_getres(), clock_gettime() and
possibly timer_create(). Besides, sem_timedwait() doesn't even let you
specify a clock ID.

-- 
Jilles Tjoelker