Fons Adriaensen wrote: > On Fri, Oct 17, 2008 at 08:06:55PM +0200, Joern Nettingsmeier wrote: > >> excuse my chiming in here, i'm not really much of a c programmer... but >> how can this >> - rb->read_ptr += n1; >> - rb->read_ptr &= rb->size_mask; >> + rb->read_ptr = (rb->read_ptr + n1) & rb->size_mask; >> fix anything? >> >> iiuc, both versions are equivalent. a context switch could happen just >> as well after the parenthesis has been computed..!? >> putting stuff on one line doesn't make it atomic. maybe you are now >> getting another compiler optimization that helps to hide the bug? > > The idea is that it is very unlikely that the compiler > would store the intermediate result in rb->read_ptr, > and so this value is updated only once. i see. but what about the other scenario: thread A reads read_ptr. thread B runs and increments it. thread A increases the old (wrong) read_ptr value by one and writes a wrong value. isn't that a problem here? -- jörn nettingsmeier home://germany/45128 essen/lortzingstr. 11/ http://spunk.dnsalias.org phone://+49/201/491621 Kurt is up in Heaven now. _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
