HI nikhil, > now if in other thread i do not follow the protocol of acquiring a lock > before access to the global variable and simply write > // > //no lock acquired here > > a--; > > //no lock released here > // > Is atomicity lost? IF you do a--; it is not an atomic operation. when split into assempbly nemonics it will be 3-4 starement before the value of the a isn really decremented.. So is the reason of using semaphores, to accomplisg this atmicity. Yes, if you do not use semaphores in this context, atimicity might be lost. > Is the consistency lost? there is a possibility > What happens if someone does not follow the standard protocol as in the > example above? dare to loose the consistency. How does this happen: lets say, When the no semaphore thread is executing, during 'a--' there is process time lapse and kernel schedules another thread i.e. with 'a++' thread, increments the thread succesfully. and when 'a--' thread runs again, you will abviously have wrong value. NOTE: kernel schedules another process when the currenly executing instrction is completed. 'a--' when atomic is considered a single instrction by kernel. So, it will not give the control to someone else before executing it. > cheers, > Nikhil > > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
