Bug #2337
closed
Wishlist: We need named POSIX semaphores
0%
Description
DragonFly is missing named POSIX semaphores (sem_open / sem_close / sem_unlink). python-multiprocessing, for example, needs this to work.
Updated by nthery about 11 years ago
- Status changed from New to In Progress
- Assignee set to nthery
I've got an skeleton prototype roughly similar to the fbsd implementation.
Semaphore names are regular files. Each semaphore has a system-wide state, basically its value, stored in a shared memory region. There is also a per-process state for dealing with multiple sem_open() calls.
The semaphore value is manipulated via atomic instructions. sem_wait() calls into the kernel (umtx_sleep()) if and only if the calling thread must sleep (semaphore value < 0). Similarly sem_post() calls into the kernel (umtx_wakeup()) if and only if there are waiters (value 0 >1). umtx_sleep() could be replaced in a subsequent step with a semaphore-optimized syscall for avoiding user<>kernel transitions when several threads concurrently call sem_wait() with value <= 0.
I'll post the code when fleshed out and cleaned up.
Updated by jalcazar almost 11 years ago
I haven't had enough time but, I did some research and was going to do the same thing (implement it similarly to FreeBSD).
https://github.com/user454322/DragonFlyBSD/commit/c0cb95785623c67b20d74bf759048d3d676e6b76
nthery: Keep up the work
=)
Updated by jorisgio over 10 years ago
- Status changed from In Progress to Resolved
Implemented by commit 1a09a5c7d3dc38e61fc28441d066b071ad659dc0