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Message-ID: <3DA2C080.3B3A@mat.upc.es>
Date: Tue, 08 Oct 2002 13:24:48 +0200
From: Francesc Oller <francesc@mat.upc.es>
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Organization: UPC
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To: linux-kernel@vger.kernel.org
Subject: futex API docs?
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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?

Basically:

P (fast P sem op):

  if (atomic_decrement(sem)<0)
    sys_futex(..,FUTEX_WAIT,....);

V (fast V sem op):

  if (atomic_increment(sem)<=0)
    sys_futex(..,FUTEX_WAKE,....);

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
sources

Can anybody help me?

Many thanks in advance

Please CC to my e-mail since I'm not subscribed.

Cheers

Francesc
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