On Wed, Oct 08, 2003 at 02:58:02PM +0200, Harti Brandt wrote: > uint8_t foo; > > (guaranteeing that the data type itself is atomic). But if a writer sets > foo as above and you read foo without locking, you might get a wrong > value: > > mtx_lock(...) > foo = 77; > > -> bar = foo; /* bar is 77 */ > > foo &= 0x1f; > mtx_unlock(...)
That part is obviuosly. > Even if you write > > foo = data & 0x1f > > it may not help (one has to understand all that stuff about sequence > points in the C-standard). Unlikely, but I agree that it might cause problems. Maybe we should have atomic_load/atomic_store without barriers to be 100% shure on that. > So you can go without locking in the reader only if: > > - the datatype is atomic (depends on your architecture) > - all writers ensure that they write only consistent values to the > variable > > The 2nd point needs very careful thinking in every case. Agreed. -- B.Walter BWCT http://www.bwct.de [EMAIL PROTECTED] [EMAIL PROTECTED] _______________________________________________ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
