Re: real POSIX.1b semaphores

Robey Pointer (
Thu, 21 Nov 1996 15:34:28 -0800 (PST)

Ulrich Drepper said this, and I just had to respond:
> One point still not clear is whether it's worth to create a
> pseudo filesystem for the named semaphores. I would vote for it
> and the standard author encourage this use. It would allow easy
> maintenance of the semaphore namespace. Keeping all names in a
> plane namespace (i.e., treating / as a normal character) would
> be simpler but once the semaphores are implemented I would think
> hundreds of semaphores used at the same time is easily possible.
> How do you like a directory with hundreds of entries? The POSIX
> people gave us this mean of structurization so me should use it.

I'm not sure how much leeway ext2 gives us here (not to mention other file
systems), but I think the cleanest solution would be to treat the semaphore
namespace as part of the filesystem, just like FIFOs are. That is, when
you create a named semaphore, it would appear as a special file in the file
system, of type "semaphore". This would require defining a new type of
file, yes, but it seems easier than implementing an entire pseudo file-

The directory information for a "semaphore special" file would just be a
pointer to kernel space indicating where the semaphore structure is.


Robey Pointer                    |  "So that's what an invisible barrier                 |   looks like."   -Time Bandits  |  (join the 90's retro bandwagon early!)