On Wednesday 07 March 2007 20:45, Stuart Macdonald wrote: > If you are on IA32 architecture then memory reads and writes are atomic > provided that they don't cross a cache line. And how do i make sure of that? declare the variable head volatile? > ----- Original Message ----- > From: "Tzahi Fadida" <Tzahi.ML2@xxxxxxxxx> > To: "Stavros Passas" <stabat@xxxxxxxxxxxx> > Cc: <kernelnewbies@xxxxxxxxxxxx> > Sent: Wednesday, March 07, 2007 11:24 AM > Subject: Re: Thread safe circular buffer. > > On Wednesday 07 March 2007 19:44, Stavros Passas wrote: > > Tzahi Fadida wrote: > > > Hi, > > > I am reading ldd3 and i am trying to understand how a circular buffer > > > without locking works. > > > If there is one writer and multiple readers. The writer has a pointer > > > to head. the readers each have a pointer of their own to tail. > > > Assumming the > > > head can't circle on the tail in time, everything is peachy. > > > However, in ldd3 the readers are sharing the tail pointer, how can this > > > be alright? (See the code in ldd3->interrupt handling->Implementing a > > > handler) At the very least you should somehow atomically grab the tail > > > into a local var and also atomically increase the tail position all in > > > one go so you won't get a race condition. > > > > Hello Tzahi, > > this code is just a sample of who interrupt handlers works, > > it doesn't guarantee anything about concurrency. > > Ok, 10x. > However, just to make sure. > If all the readers have their own tail then there is no problem right? > If they want to share the tail, they have to use locking right? > Moreover, i was wondering if when i code the following: > count = head - tail. > Can i say for sure that the head itself will not be corrupted while > calculating? i.e. if it was 0xffffffff and it is being concurrently changed > to 0xeeeeeeee i won't get a head variable in the calculation that contains > 0xeeeeffff? If it does that i don't know if it is even safe with one writer > and one reader... -- Regards, Tzahi. -- Tzahi Fadida Blog: http://tzahi.blogsite.org | Home Site: http://tzahi.webhop.info WARNING TO SPAMMERS: see at http://members.lycos.co.uk/my2nis/spamwarning.html -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
