El Mon, Mar 19, 2007 at 06:04:38PM +0530 Daniel Rodrick ha dit: > On 3/19/07, Momchil Velikov <chill@xxxxxxxxx> wrote: > >Daniel Rodrick wrote: > >> I may be wrong, but from what I understand, the count passed in the > >> semaphore initialization > >> > >> sema_init(sem, count); > >> > >> is the number of threads that are allowed to hold the semaphore > >> simultaneously (no of threads that are allowed to enter their critical > >> sections simultaneously). So can't a semaphore be actually held > >> recursively? > > > >Semaphores are not "held". See below. > > > >> Also, the only difference I could find between a semaphore and mutes > >> is that a mutex is a specail and most common form of semaphore where > >> only one thread can get it at a time. Are there any other differences? > > > >The difference is that a semaphore has no owner. Neither semaphores nor > >mutexes are a "special form" of the other - they are fundamentally > >distinct mechanisms. > > > > But I see mutexes implemented using semaphores only: > > #define __DECLARE_SEMAPHORE_GENERIC(name,count) \ > struct semaphore name = __SEMAPHORE_INITIALIZER(name,count) > > #define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1) > #define DECLARE_MUTEX_LOCKED(name) __DECLARE_SEMAPHORE_GENERIC(name,0) that's the deprecated mutex API based on semaphores, AFAIK the one described in http://lwn.net/Articles/167034/ should be used m. -- Si deseas mantener tu libertad, debes estar preparado para defenderla (Richard Stallman) .''`. using free software / Debian GNU/Linux | http://debian.org : :' : `. `'` gpg --keyserver keys.indymedia.org --recv-keys B9A88F6F `- -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
