On Fri, Jun 21, 2002 at 05:11:26PM +0300, Momchil Velikov wrote: > >>>>> "Alan" == Alan Stern <stern@rowland.org> writes: > Alan> But you didn't answer my first question. What are the essential > Alan> differences between a struct completion and a semaphore? > > Hell if I can find any difference. Except that semaphores (in Linux > (the kernel)) have machine dependent implementations and are likely to > be much faster. There is no "down" for completion. For semaphore, if you "up", exactly one "down" succeeds. For completion, it you "compelte", all "wait"s succeed from now on. You have to reinitialize it. And initializing is not atomic. So completion is really just an encapsulation of waitqueue whith conditional variable to simplify wait_on_event. The semaphores are much more complicated and much more widely used, thus tjey are partly in assembly. Anyway, you CAN'T use completion for mutual exclusion and semaphores are not much good for waiting on completition (they are good for producer-consumer, but that's something else) ------------------------------------------------------------------------------- Jan 'Bulb' Hudec <bulb@ucw.cz> -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
