>>>>> "Jan" == Jan Hudec <bulb@ucw.cz> writes: Jan> 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. Jan> There is no "down" for completion. For semaphore, if you "up", exactly Jan> one "down" succeeds. For completion, it you "compelte", all "wait"s Jan> succeed from now on. You have to reinitialize it. And initializing is Jan> not atomic. So completion is really just an encapsulation of waitqueue Jan> whith conditional variable to simplify wait_on_event. Not true. See the handling of the ``done'' field. It is uncremented in ``complete'' and decremented in ``wait_for_completion''. Just like the semaphore count. Jan> The semaphores are much more complicated and much more widely used, thus Jan> tjey are partly in assembly. *shrug* Jan> Anyway, you CAN'T use completion for mutual exclusion and semaphores are Of course, you CAN :) Just initialize it to 1 and than ``wait_for_completion'' is equivalent to lock and ``complete'' is equivalent to unlock. Regards, -velco -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
