futex API docs?

From: Francesc Oller (francesc@mat.upc.es)
Date: Tue Oct 08 2002 - 06:24:48 EST

Hi all!

I've been trying to understand how futexes work looking at the last
dev. kernel. I've not found any docs. Are there any?


P (fast P sem op):

  if (atomic_decrement(sem)<0)

V (fast V sem op):

  if (atomic_increment(sem)<=0)

Futexes need be counting semaphores since there could be WAKEs in
the middle of atomic_decrements and WAITs (not atomic) but I do
not see this in the code. I can't find the kernel counter in the

Can anybody help me?

Many thanks in advance

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