Pino Toscano, le Mon 02 Apr 2012 22:33:36 +0200, a écrit :
> @@ -103,6 +104,16 @@
> mtime->microseconds = (time)->microseconds; \
> asm volatile("":::"memory"); \
> mtime->seconds = (time)->seconds; \
> + asm volatile("":::"memory"); \
> + mtime->clock_rt.seconds = (time)->seconds; \
> + asm volatile("":::"memory"); \
> + mtime->clock_rt.nanoseconds = \
> + (time)->microseconds * 1000; \
> + asm volatile("":::"memory"); \
> + mtime->clock_mt.seconds = (monotonic)->seconds; \
> + asm volatile("":::"memory"); \
> + mtime->clock_mt.nanoseconds = \
> + (monotonic)->microseconds * 1000; \
> } \
> MACRO_END
>
This does not actually bring read safety. The original code uses
memory barriers to make sure that microsecond update happens
between check_seconds and seconds are updated, so that code like
record_time_stamp works. That part needs to be kept as is for
compatibility, and additions need to implement something similar. Just
putting memory barriers will not work, you'd also need a similar
check_foo field, and test it in the reader part; or use a generation
number, like xnu's commpage_set_nanotime, something like:
sav = mtime->generation;
mtime->generation = 0
asm volatile("":::"memory");
mtime->clock_rt.seconds = (time)->seconds
mtime->clock_rt.nanoseconds = (time)->microseconds * 1000.
mtime->clock_mt.seconds = (monotonic)->seconds
mtime->clock_mt.nanoseconds = (monotonic)->microseconds * 1000.
asm volatile("":::"memory");
mtime->generation = sav+1;
Samuel
